0 ·<-e ANALYSIS OF FRESHWATER INFLOW EFFECTS ON METABOLIC STRESSES OF FISH IN CORPUS CHRISTI, SAN ANTONIO, AND MATAGORDA BAYS Final Report to Texas Water Development Board for TWDB Contract No. 14-60020 (IAC-7677-0632) (with Appended Data) • THE UNIVERSITY OF TEXAS MARINE SCIENCE INSTITUTE Port Aransas Marine Laboratory Port Aransas, Texas 78373 Phone '12 749-6711 October 12, 1976 Texas Water Development Board Stephen F. Austin Building Austin, Texas 78701 · Gentlemen: With great pleasure, I am submitting herewith the final report, "Analysis of Freshwater Inflow Effects on Metabolic Stresses of Fishes in Corpus Christi, San Antonio, and Matagor~a Bays," sup­ported under contract IAC-7677-0632. All of us involved in this study gratefully acknowledge the support of TWDB. • The results are quite straightforward and provide a useful addition to the knowledge of seasonal characteristics of south Texas waters and their fishes. Further, the work used in this report has suggested several new lines of research endeavors that are to be the subjects of a Master's thesis and a Ph.D. disser­tation. Prefixing the report is an "executive summary" that includes the general rationales, the results in abbreviated form, and a recommendation for extended studies to include other coastal fishes using the new techniques developed in this study. The technique of assessing salinity optima by measuring maximum sus­tained swimming rates may turn out to be an inexpensive, rapid ,and easily applicable technique. . Work on this project has been a rewarding experience in terms of cooperation among all those involved at administrative, research and technological levels. Respe~tfully submitted, • ~-~--M r:E,'(~~ Donald E. Wohlschlag Professor · DEW: jp Encl: 25 copies • • FINAL REPORT to Texas Water Development Board for TWDB Contract No. 14-60020 (IAC-7677-0632) · ANALYSIS OF FRESHWATER INFLOW EFFECTS ON METABOLIC STRESSES OF FISH IN CORPUS CHRISTI, SAN ANTONIO, AND MATAGORDA BAYS Donald E. Wohlschlag Principal Investigator The University of Texas at Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373 • 11 October 1976 EXECUTIVE SUMMARY • General Considerations This study involves the rationales for: (1) investigation of freshwater inflow effects on South Texas estuaries and bays; (2) utilization of fish as indicators for optimal effects of these inflows; and (3) the use of metabolic and swimming rate techni­ques for the assessment of inflow effects independently of fishery and pollution effects. The purpose of this study is to evaluate stresses related to freshwater influxes on the coastal subadult to adult spotted sea­trout or "speckled trout" (Cynoscion nebulosus), which is highly • valued for food and recreation. The balance among freshwater inflows, evaporation, and sea­ water influxes directly determine the salinities of the coastal bays and estuaries, which biological experience indicates function best at less than seawater salinities (35 parts per thousand,ppt). Only fresh waters (zero ppt salinity) via streams and rivers can naturally maintain estuaries and bays at less than seawater sal­inities and at maximum biological productivity. What is the optimal salinity -or salinity regime -and how ·much freshwater inflow is necessary to maintain optimal salinity regimes for any given species (-0r for the entire ecosystem) are questions of utmost importance for maintenance of bay and estuarine product~vity. That salinity is a natural stress whose minimal • effects can be identified for the spotted sea trout is the basis of this study. -ii­ • The basis of indefinite survival of a species like the spot­ted sea trout is that it be considered as a successful integrator that can optimize all the living and non-living environmental factors, many of which can be occasionally stressful. For swimming fishes, as well as for distance runners, race­horses, etc., maximum sustained performance depends upon optimum internal and external environmental circumstances. At a maximum sustained performance level, metabolism as measured by oxygen con­sumption rate is also maximal. A normal organism at zero activity · under optimal environmental conditions has a standard (maintenance, or basal) metabolic level that is the lowest level . for short term survival without energy expenditures for growth, foraging, assimi­lation, reproduction and other required functions. If an organism • survives at all below the standard metabolic level, it will lose weight, show some degree of morbidity, and not be able to carry out completely these functions. At some energy level between the maximum sustained and the standard (maintenance) metabolic levels is the level of routine metabolism that is high enough to account for these normal func­tions. The difference between the standard and the routine met­ abolic rates is the scope for routine activity. Similarly the difference between the standard and the maximum sustained swim­ ming metabolic rates is the scope for maximum activity. Either of these metabolic scopes for activity is a measure of the well being of a fish, · independently of extraneous stresses • such as those from fisheries. The maximum scope is especially sensitive to general, sublethal environmental stresses. -iii­ • The idea of scope and its interpretations are shown .diagram­matically in the figure, where hatched and cross-hatched portions are standard metabolic levels. At optimal conditions the maxi­mum scope is given in (b). When a natural stress like salinity is applied at higher or lower than optimal levels, the maximum scope must decrease because extra maintenance work is required for salt regulation, i.e., the standard or maintenance level must be raised, thus reducing the scope as in (a) and (d) in the figure. (If a stress like a chemical pollutant is not natural, it is like­1~ that the body's biochemical machinery will ultimately break down, lower standard metabolism, and result in morbidity or death)~ When less than optimal conditions prevail among natural stresses like salinity, or with sublethal stresses like pollutants, • the maximum metabolic levels are depressed as in (d). A possibil­ ity of reduced activity and scope without a change in standard level is shown in (c). In all cases the routine scope and the routine metabolic level is less than for the maximum scope and maximum metabolic level. Scope can thus only decrease under stress either by reducing the activity metabolic level, by increasing the standard level, o~ by both . • -iv­ ... J <-' z :E :E - 3: (/) c LLJ z :r: en Cl [. LLI ...._ :E CJ) :::> <{ ~ LL x· ...J <{ <{ ~ ~ a:: a:: 0 0 z LL l1J a. 0 (.) . CJ) • ...... .... .. . .. .. .. .. .. . ... . . ... . .. . . ... .. .. . . .. .. ,, .. .. .. . . . .. . .. . . . .. ~ . ... .... .. . .. .. .. . .. .. . .. . . .. .. . . . . . . . . . . .. . . .. . . . .. . . .. .. ... .. . . .. 3 dO~ s 0 .. . . . .. . . ... .. .. . . .-. .. . .. . .. . .. . .. .. . . . 3 dO ~ s :a dO 0 s 0 • Results _., In all cases of this study on the spotted sea trout, both the scope at maximum sustained swimming levels and the scope at the routine levels were the greatest at about 20 ppt salinity for fish in seawaters of various concentrations or dilutions. .... Salinity is optimal at about 20 ppt for summer temperatures of 280 C and for winter temperatures of 150 C. There appear to be no temperature shifts in salinity effects. .... At about 10 ppt and at about 45 ppt, the standard (maintenance) requirements are about double those at 20 ppt. ... At about 10 ppt and at somewhat less than 45 ppt, the routine metabolic levels are about high enough (double the standard rates). to allow for minimal foraging, assindlation and growth. • .... From about 10 ppt to 45 ppt in natural coastal waters is the normal range for the occurrence of the spotted sea trout with most catches usually in waters from about 15-35 ppt. .... Studies of routine and standard metabolic rates at selected temperatures from 15° -25°c and selected salinities from 10 -32 ppt for waters variously from Nueces, San Antonio and Lavaca (Matagorda) Bays revealed that these waters in 1976 caused no appreciable decrease in scope values that could be construed to result from sublet~al pollution. .... In summer of 1975, but not 1976, the Nueces Bay waters caused · an increase in standard metabolism, presumably caused by an un­identified sublethal stress. • .... In autumn 1976, the spotted sea trout were in a starved con­dition that was progressively worse for the larger fish. At this -vi­ • time both the standard and routine metabolic determinations at 35 and 45 ppt were depressed. The data suggest that, at given feeding levels, adequate scope for maintenance, and possibly for weight gains, would be likely only at less than 35 ppt • ..-. In experiments at maximum sustained speeds for an hour or more, the speeds themselves are maximal at an optimum salinity of about 20 ppt for the spotted sea trout. It is suggested that maximum sustained speeds alone could be used for the identification of an optimal salinity level. (Routine speeds are not always directly related to optimal salinity). Recommendations .._. It is recommended that both the maximum metabolic scope and • the maximum sustained swiniming speed methods of identifying the optimal salinity level be extended to other selected coastal fishes of importance in South Texas waters . • -vii­ • INTRODUCTION The purpose of this study is to evaluate quantitatively the relative importance of freshwater influxes on ·the metabolic re­ sponses of the spotted seatrout, Cynoscion nebulosus. This species is important to recreational and commercial interests along the south Texas coastal, bay and estuarine systems. The rationale of the evaluation in this study, which was examined in a preliminary pilot study during July and August 1975, indicated that respiratory metabolism responded directly to salinity levels of both seawater and waters from Nueces Bay, a secondary bay adjacent to primary Corpus Christi Bay. The measurements that are pertinent include respiratory metabolic responses at standard, or maintenance, levels, active metabolism and swimming rate; and either • "scope for routine swimming activity" or '.'scope for maximum sus­tained swimming activity" as elucidated by Fry (1947). Scope is the difference between active metabolic rates and standard (main­tenance) rates at given environmental conditions. Original data on temperature optimization studies by Fry indicated clearly that "scope'' was maximal at optimal temperatures, when scope was defined as the difference between active and standard, or maintenance, metabolic levels. Both theoret.ical and practical studies have indicated that with a given energy input any biological system under stress results in a system with reduced energy output when compared to a system that is unstressed and optimal. Since Fry's (1947) study on metabolic scope and its maximi­zation at optimal temperatures, numerous authors, including Fry • (1957, 1971), have extended the concept of metabolic scope to various species and environmental circumstances. Brett (1958, • 1964, 1965, 1971) and Brett, et al. (1969) have extended the con­cept to actively swimming salmon over a variety of environmental and feeding conditions. More recently Webb (1975) has reviewed several important features of hydrodynamics and energetics of swimming fish that are important for the interpretation of maximum scope at various stresses. For Texas Gulf fishes, Wohlschlag and Cameron (1967) showed that a very low sublethal pollution level would tend to depress total metabolism much more at temperature extremes that at optimal temperatures. Wohlscblag, et al. (1968) demonstrated the nature of pinfish metabolism at routine and standard metabolic levels. Also, for the pinfish, Kloth and Wohlschlag (1972) noted that the swimming velocities tended to decline with increasing salinity, • while very insignificant, sublethal pollution levels tended to depress total metabolism. A series of detailed studies of the Gulf coastal striped mullet tended to follow the same stress­metabolism patterns with respect to salinity, temperature, and water quality variations. In field studies, throughout the year with pronounced seasonal changes in metabolism, the levels of total metabolism for mullet in water at 30..:.35 ppt salinity wer.e always higher than in more brackish waters from San Antonio to Baffin Bays (Wohlschlag and Moore, ms.). The energy requirements to meet environmental stresses thet result in increasing the maintenance (standard metabolism) requirements are considerable (Cech and Wohlschlag 1973, ms.). The scope for activity of the mullet also appears to be depressed under the • slight pollutional stresses throughout the year in Galveston Bay (Wohlschlag, et al. ms.). Late summer stresses also appeared to 3 • depress metabolism in Galveston Bay and to depress growth rates as well, presumably during the prolonged mid-to-late summer thermal stress (Cech and Wohlschlag, 1975). Nordlie and Leffler (1975) and Collins (MA thesis, Univ. Texas) note that the mullet isosmotic point is about 11 ppt, the point of minimal standard metabolism. There is a slight metabolic increase in less saline waters and a doubling of standard metabolism at about 45 ppt for these mullet. In the preliminary 1975 July-August investigation, "A Pilot Study to Analyze Effects of Freshwater Inflows and Metabolic Stresses for Important Fish Species in Corpus Christi Bay, Texas," we have shown that the routine scope--the difference in metabolism between routine and standard levels--is optimal at a salinity of • about 20 ppt. For seawater, the scope drops rapidly below and above this optimum. In the same pilot study, both the standard and routine metabolic levels of fish in Nueces Bay waters at 15 and 25 ppt were elevated to the extent that there was a strong im­plication of sublethal stresses not present in various concentrations of sea water. Presumably it would be impossible to increase the maximum energy output by increasing sustained · maximum swimming rates, since these rates have an upper limit determined by the biological-biochemical systems under aerobic conditions and at specified temperature and salinity regimes. It is therefore reasonable to predict that in all natural or man-induced stress situations at sublethal levels, the scope for aerobic activity must necessarily decrease by (1) raising • the maintenance (standard) metabolism, (2) reducing the active metabolic level, or (3) by simultaneously increasing the standard • and reducing the active levels. For the spotted seatrout with a rather clearcut summertime 28°c optimal routine scope at about 20 ppt seawater salinity, the immediate questions arose as to the practical utility of extending this study through the remainder of the year at other salinities and temperatures, along with other variable, but unknown, seasonally changing ecological situations pertinent to the spotted seatrout. The seasonally extended evalu­ation of scope for routine activity is thus one of the major aims of this study. The second major aim of the study is to draw some inferences about effects of waters in Nueces, San Antonio, and Lavaca Bays on metabolic scope at the routine level in order to ascertain whether any of these waters might have adverse stress effects on • the scope that might be confused with freshwater influx effects. The third major aim is (a) to evaluate with the new Blazka chamber metabolic scope at maximum sustained swimming speeds for the assessment of freshwater influx effects, and (b) to evaluat~ t.he maximum sustained swimming rates themselves at different salinities . • ;. ' " .. ..... ~ . . -· MATERIALS AND METHODS General • 5 Since this study followed essentially the procedures de­tailed in the pilot project, only the essentials of the operations will be given when procedures are identical. New or modified Fry (1971) gives an procedures will be given in more detail. overview of these and related techniques. Fish and Acclimation The spotted seatrout, Cynoscion nebulosus, were obtained from various local sources by using live shrimp baited hook-and­ line techniques. In October fish were taken from the Barney Davis Power Plant cooling pond, and later in the year from the intake canal off Laguna Madre. During winter and later they were obtained • • from near the Lydia Ann Channel near Port Aransas. Several small winter collections were made at the Rockport boat basin. Fish were transported to the laboratory as soon as possible and held in large circular tanks at temperatures and salinities corresponding to the natural source waters. Acclimation was carried out in the experimental temperature controlled aquaria with 24-48 hour acclimation to temperature and salinities that initially were near ambient conditions at the source of waters. For major salinity changes of 5-10 ppt and temperature changes of 5°c, about 2-3 additional days were allowed for acclimation. It is most important to note that the metabolic rate deter­minations were always made in the same waters in which fish were acclimated. Control was to ±o.1°c . Salinities of the laboratory seawate~ supply were adjusted to lower levels by adding deionized water or to higher levels by • the addition of sea salts. Control was maintained to about ±0.1 ppt. • Determination of Respiratory Metabolism at Routine and Standard Levels The techniques for measuring routine metabolism follow those of the pilot project as described and evaluated by Wohlschlag and Juliano (1959), Wohlschlag and Cameron (1967), Wohlschlag, et al. (1968) and Wohlschlag and Cech (1970). Acclimated fish were placed in a 42.12 liter clear plastic circular (annular) metabolism chamber that could be rotated at variable speeds by a constant torque motor mechanism from which the chamber was suspended. The swimming track was 2 m per revolu­tion. The entire chamber was immersed in the acclimation aquarium. With a minimum of handling each experimental fish was introduced into the chamber through a sealable hatch. Water samples for oxygen analysis were withdrawn through a small outlet tube from the chamber; replacement water was added _through an inlet tube attached to a funnel. Just as soon as the fish had become "adjusted" to the chamber, it was rotated at whatever speed the fish would swim consistently, the revolution counter reading was noted and counts were recorded for the usual 15-min intervals between removal of water samples for o2 analysis. For very small fish, the time intervals between o2 analysis were as long as 30 min. Ordinarily there were the initial and three additional equally spaced intervals at which the o2 level in the chamber was determined. With chamber o2 levels • corrected for water withdrawn and added, a simple regression of the decline in 02 against time provided the value for rate of 7 oxygen consumption in mg hr-1 . At the termination of the run data on fish length, weight and sex were recorded. Oxygen measurements were by means of a Radiometer PHM-71 acid-base analyzer and an E-5046 oxygen electrode with an appro­priately thermostated system. Initial o2 levels and acclimation . regimes were near saturation; levels were no lower than about 65% saturation at the termination of individual experiments at the higher temperatures with the largest, most active fish. The rate of 02 consumption as mg 02 hr-l and as mg o2 kg-l hr-l was calcu­lated for each fish and tabulated with temperature, salinity, body weight and length, and swimming velocity (cm sec-1 and body lengths sec-1 ). The protocol for each experimental set of about 10 fish at a given salinity and/or temperature is given later under separate headings that pertain to experiments with the various bay and sea waters. Except for portions of the Blazka respirometer experiments described below, the oxygen consumption rates may be linearly related to the several dependent variables as A Y = a + bw Xw + bs Xs + bv Xv where y~ is the expected log mg ·0 2 consumed per hour, a is a constant, bw is a partial regression coefficient of the increase in Y per unit increase in log weight at a constant salinity and swimming velocity, Xw is the log weight in grams, • bs is the partial regression coefficient of the increase A or decrease in Y per unit change in ppt salinity at a constant weight and swimming velocity, is the salinity in ppt, X8 bv is the partial regression coefficient of the increase A in Y per unit increase in swimming velocity at con­stant weight and salinity, and Xv is the swimming velocity in fish lengths as cm sec-1 .. If temperature Xt was a dependent variable with a partial regres­sion coefficient bt, the term bt Xt was added to the above equation. The linear first-order multiple regression proced~re follows that of Wohlschlag and Juliano (1959), Wohlschlag and Cameron (1967), Wohlschlag et al. (1968) and Wohlschlag and Cech (1970). The • techniques are given in most statistical manuals, e.~., Snedecor and Cochran (1967). The combinations of data used in various regression calcu­lations are given in the appropriate tables in the section on results. Initially the regressions were calculated by use of two sets of about 10 experiments each that were at adjacent salinity intervals, so that about 20 experiments would yield an estimate of the oxygen consumption rate over a small salintiy range at a given temperature and in other cases over a small temperature range at a given salinity. Various other regressions were calculated to cover more data over larger temperature and salinity ranges. • Standard respiratory metabolic rates were extrapolated by using the original data sets of about 10 determinations plotted 9 • as log 02 consumption kg-1hr-1against swimming velocity Xv, so that the lowest of the individual rates could be extrapolated to Xv = 0. This method (Brett, 1964) has been checked by Moore (1976) for the striped mullet and found to be in good agreement with 1 direct determinations of the standard rate with minimally quiescent fish. One or more of the calculated multiple regres­sions pertinent to the subset data range was/were used to extra­polate from the lowest data point back to Xv = O, provided the regression Y"' (on a per kilogram basis) calculated with the subset average log wts, swimming velocities, salinities and temperature passed through or very near the subset Y kg-l and Xv· If this regression passed near these means, it should be noted that its Xv = 0 value would be considerably higher than the Xv = O value • • plotted from a line parallel but through the minimum value(s). This is the same procedure utilized in the pilot study for the estimation of the standard rates. It should be noted here that another thesis research project on spotted seatrout metabolism has yielded minimal standard metabolism rates (over 24-hr con­trolled conditions) that are remarkably similar to those of this study. Hopefully these unpublished results will be available in published form within a year. Metabolism at Maximum Activity The Blazka "swimming tunnel" was set up and calibrated for measuring oxygen consumption rates of fish swimming at maximum sustained, and intermediate, swimming levels. The locally constructed Blazka chamber provided an ideal technique. The chamber, considerably modified from the original ; ,_ .~: . .,.,.. ~., . :·~ • designs (Blazka, Volf, and Cepela, 1960; Smith and Newcomb, 1970), is relatively easy to use for measuring o~ygen consumption rates and swimming rates up to at least 6 body lengths sec-1 for a fish as large as 4b cm long. Essentially the clear acrylic plastic chamber is a 19 cm ID tube for the fish and an outside 29 cm OD tube. Water is drawn through the inside tube by means of a pump impeller powered by a 10 hp constant torque variable speed motor. The flow is redirected via a fiberglass (glass reinforced plastic) cone within a dome back through the outside tube, through a cone and dome redirection, and back through the inside tube containing the fish. The chamber flow is preceded by a set o·f ''egg-crate" baffles and two 4 mm screens to "linearize" the flow as described by Mar (1959) for water tunnels of the type used by J. R. Brett • in his extensive studies. A screen in the cone in front of the . impeller and behind the fish effectively excludes a fish from the impeller. The 63 cm respiration chamber is detachable from the cone-and-dome arrangements at each end; when in use it is gasketed and "qui6k-lock'' clamped at each end to the cone-and-dome arrange­ments. The entire 207-liter rig is suspended from an overhead trolley so that when it is opened by unclamping and unsealing the aft portion of the respiration chamber, the entire fore part of the rig can be moved away from the cone-and-dome arrangement containing the impeller. The entire rig is suspended in a tempe­rature controlled aquarium making the addition or removal of fish and the cleaning of the chamber an easy task. The motor shaft • goes through a stuffing box in the aquarium wall against, which is bolted the cone-and-dome arrangement containing the impeller. • In the fore and aft top part of the respiration chambers are two 30 mm access tubes cemented between the outer and inner tubes. A paddle wheel electronic transducer type of yacht speedo­ meter mounted on the end of a tube slightly smaller than 30 mm fitted with two 0-rings can be inserted into either access tube and at any vertical level to measure flow rates, which are read directly from the speedometer mounted outside and attached via the coaxial wire inside the tube on which the transdu~er unit was mounted. Impeller shaft speeds are measured by means of a stroboscopic revolution counter system. The shaft RPM was then· calibrated and collated with the speedometer readings at vertical flow-rate pro­files across the diameter of the inner respiration chamber tube • to create flow profiles across the tube. It is then possible to measure the flow rate and swimming speed by direct reading of the shaft RPM so that the access hole can be plugged when metabolic runs are made. With few exceptions fish tend to swim in the maximum velocity portion of the flow-rate profile near the center of the tube. To prevent some fish from nosing up to the anterior screen (and thus altering or "blocking" the flow-rate profile), the addition of small 5-10 cm long x 2-4 mm wide plastic streamers on the screen served well. Details of the hydrodynamics of fish swimming that are pertinent to flows in such a chamber are given by Webb (1975). When the chamber was immersed and filled, oxygen bubbles were bled from outlet-inlet-tubes with stopcocks at the uppermost • water level in the cone-dome junctures. For oxygen analyses, 12 water samples were withdrawn by syringe through a capillary tubing through a stopper in one of the 30 mm ·access tubes to the respiration chamber. As may be noted in Table 14, the protocol for use of fish sometimes resulted in successive measurements on one fish. The total times of the runs varied from 1-3 hours depending on the size of the fish and swimming speeds. All fish were run at 2a 0 c and at salinity levels of 10, 15, 20, 25, 30, 35, 40 and 45 ppt. At zero velocity several fish were in the chamber 8-12 hours overnight, after which the impeller was run briefly before oxygen samples were drawn. The results were first treated by both averages for each salinity and maximum sustained swimming velocities. The next procedure was to work out the multiple regressions for adjacent Finally linear equations salinity levels as for the above data. of the third and fourth orders that related the average oxygen consumption rates per kilogram at maximum swimming rates to the salinity were calculated by the methods outlined in Snedecor and Cochran (1967). Source of Waters for Experiments Sea water from the Port Aransas Marine Laboratory was used · throughout for the sea water experiments. No pollution or contamination was ever noted for these waters during the year. Waters from Nueces, San Antonio and Lavaca Bays were obtained by pumping into four 500-gal. tanks on a barge towed to the sampling sites and back for use in the laboratory. These sites are: • Nueces Bay USGS Line 53, Site 3 San Antonio Bay USGS Line ~64, Site 2 Lavaca Bay USGS Line 90, Site 3. The series of 1975-76 experiments and pertinent Tables for . data were based on waters as follows: Nueces Bay October-November 1975 (Table 1) Sea Water November-December 1975 (Table 5) Sea Water January-February 1976 (Table 6) San Antonio Bay February-March 1976 (Table 8) Lavaca Bay April 1976 (Table 10) Nueces Bay May-July 1976 (Table 12) Sea Water (Blazka) July-October 1976 (Table 14) In addition~work on San Antdnio and Lavaca waters is con­ • tinuing, but will not be included in this report. Blazka sea water experiments at 10, 40, and 45 ppt are appended in Table 14 . • 14 • RESULTS Autumn Nueces Bay Waters At the termination of the pilot project in August 1975 the only salinity effects in Nueces Bay waters investigated were at 15 and 25 ppt. By October-November these studies began at 35 and 45 ppt to provide metabolic comparisons with fish in sea waters at the same salinities. The results of these determinations are in Table 1. When the standard and active metabolic levels appeared to have the opposite relationship of Nueces Bay water experiments from the 1975 July-August data in comparison to seawater data, it was noted that the spotted seatrout by late summer and autumn were notably thinner than summer fish, and in some cases actually appeared to • be emaciated. (Mr. Ernest Simmons of the Texas Parks and Wild­life Department, Rockport in personal communications noted that spotted seatrout from Laguna Madre were often too emaciated to be sold commercially at that time.) Accordingly, the 1975 summer and the 1976 autumn fish were compared by means of log weight-log length regressions given in Table 2 with analysis of covariance statistics in Table 3. The slopes differ considerably; the bs = 2.71 is much greater than the abnormally low ba ~ 1.80. From Guest and Gunter (1958) a value of 2.91 was calculated for comparison of the log weight-log length regression slope pertinent to much more normal, well­nourished conditions. From the analysis of variance data in Table 3, the log weights for length-adjusted means are also different. • The equations in multiple regression form for the autumn and summer data (from the pilot project, where pertinent) are in Table 1. Autumn data for nultiple regression calculations of spotted seatrout respiratory metabolism rates in relation to selected salinities of Nueces Bay (NB) waters, fish weights and lengths, and swimming velocities. Temperature controlled at 28°c. Swimming Log mg Log mg Log Velocity Experiment Salinity Length Weight (Lsec-1) 0 hr-1 o2 Kg-1 hr-1 2 Date Number {ppt) (mm) (g) (cm) 5 x 75 NB3A 35 346 2. 5416 0.87 1.9288 2.3872 6 x 75 NB3B 35 315 2.4771 0.45 1.8209 2.3438 NB3C 35 351 2.6107 1.03 2.0747 2.4640 NB3D 35 360 2 .6415 0.89 2.0700 2.4285 NB3E 35 360 2.5933 0.46 1.9957 2.4024 NB3F 35 395 2.7126 o. 76 2.0510 2.3384 NB3G 35 431 2. 8363 o. 36 2.0721 2.2358 NB3H 35 396 2.7709 0.62 2.0997 2.3288 7 x 75 NB3I 35 444 2.8585 0.28 2.1672 2.3086 NB3J 35 359 2.6191 a.as 1.8471 2.2280 NB3K 35 305 2.3222 0.75 1.8267 2.5045 NB3L 35 298 2.3345 0.33 1. 5809 2.2465 NB3M 35 307 2. 3692 0.65 1.9826 2.6134 I-' NB3N 35 294 2.3304 0.81 1.7683 2.4379 \.n NB30 35 285 2.2718 0.62 1.8631 2.5913 (Table 1 cont.) Means 35.0 349.7 2.55264 0.649 1.94325 2. 39061 20 x 75 NB4A 45 304 2.3345 0.53 1.8341 2.4996 NB4B 45 290 2.2788 0.71 1. 7625 2.4837 NB4C 45 270 2.1790 0.83 1.8153 2.6363 NB4D 45 295 2.3541 0.61 1.8412 2.4871 NB4E 45 332 2.5079 o.oo 1.8816 2.3738 23 x 75 NB4F 45 150 2.4771 0.00 0.9912 1. 5144 NB4G 45 341 2.4757 0.27 1.9410 2.4653 NB4H 45 392 2.6721 0.42 2.0032 2.3309 NB4I 45 284 2.2718 o.oo 1. 7077 2.4359 NB4J 45 199 1.7924 0.78 1. 3655 2.5731 · 5 XI 75 NB4K 45 287 2.2601 0.70 1. 7959 2.5359 NB4L 45 300 2.3404 0.60 1.8006 2.4602 ' NB4M 45 320 2.4330 0.56 1.8421 2.4091 NB4N 45 248 2.1106 0.57 1.6138 2.5033 Means 45.0 286.6 2.32054 0.470 1. 72825 2.40774 I-' 0\ ~ . "'. .... .. , .•: n ,\, _. ......,... • Table 2. Analysis of covariance of log weight-log length relationships between surruner and autumn groups of Cynoscion nebulosus. Sums of squares and products, and regression coefficients. (Tabulated values rounded to four decimal places.) Source of Variation Within Summer Within Autumn Within Seasons Between Seasons • Total Degrees of Sums of Squares and Products Regressions Freedom lw 58 0.1607 1.4310 0.4357 bs = 2.7102 28 0.2529 1.4955 0.4540 bA = 1.7954 86 0.4137 2.92659 0.8898 ba = 2.1509 1 0.0671 0.95010 0.2526 bm = 3. 7613 87 0.4808 3.8766 1.1424 b0 = 2.3758 Regressions of log weight (g) on log total length (rrun) Summer fish: log weight= -4.3821 + (2.7102)(log length) Autumn fish: log weight = -2.0382 + (l.7954)(log length) • 18 • Table 3. Data for analysis of covariance of log weight-log length relationships for Cynoscion nebulosus in summer and autumn samples. (Tabulated values rounded to four decimal places.) Errors of Estimates Source of Variation DF Sums of Squares Mean Squares Deviations from linear regressions within seasons 84 S1 = a. 93a2· a.a11a Differences between season regressions 1 S2 = a.a822 a.a822 Deviations within seasons from average regression ba 85 S1+S2 = i.a125· a.a119· Deviations between seasons from mean regression bm a S3 = a.a a.a • Differences between ba and bra 1 S4 = a.1498 a.1498 Deviations between seasons for testing significance of "adjusted" means 1 S~S4 = a.1498' a.1498 Total deviation from regression b0 86 S1+S2+S3+S4 1.1622 Tests of significance: a.a02 •••/' ­Slopes: 7.43(1, 84DF)1d~; a. as> P>a. al / a.all. •• ­ a .149 •••/ Adjusted means: F = MS4 (MS1+MS2) = /a.all••• = 12. 58 (1, 85DF)1~~·~ a.as ::»P >a.a1 • 19 • Table 4. These data are unusually variable but the bw and bv I coefficients are statistically significant at less than the P<0.01 level. The small salinity coefficients, bs, are not statistically significant. The autumn Nueces. Bay standard and routine metabolic levels at 35 and 45 ppt can be compared with the summer data at 15 and 25 ppt, in relation to the entire salinity range for the summer standard and routine levels as in Fig. 1. Quite clearly the autumn Nueces Bay levels are depressed to correspond with the weight-losses and witn incipient or actual morbidity. Autumn and Winter Sea Water Series These data are for the purpose of comparing salinity effects on standard and routine metabolic levels and routine scope to • determine whether optimum scope values shift from the summer optimum of about 20 ppt. The November-December data in Table 5 are all collected at 25oc, a moderately high late autumn temperature. The winter data at 15°C for January-February in Table 6 represent a fairly realistic low temperature representative of most winters in south Texas coastal waters. The salinity differences in both series are small (14-25 ppt) and would be generally representative of coastal primary and secondary bays north of the Laguna Madre. Table 7 contains the multiple regression equations for ad­jacent, and various combinations of, salinity levels for the separate autumn and winter series. All the weight, bw, coefficients are highly significantly different from zero. Salinity coefficients • bs, are significant at least below P<0.05 for equations 12, 14, 15, and 17. Swimming coefficients, bv, are significant at or below :" ') Table 4. M.lltiple .regression equations for oxygen consumption rates of Cynoscion nebulosus in Nueces Bay waters at salinities of 35 and 45 ppt and at 20oc. Autumn 1975; also Sununer 1975* plus Autumn 1975 to include lower salinities. Expected Velocity, Xv, Multiple Experiment Salinities Log Wt., xw Salinity, Xs Lengths (cm) Correlation Log ml Numbers (ppt) N 02hr-Constant (g) (ppt) (L sec-1) R - .... NB24A-Ja (7) 24-35 24 y = -0.3024 +0.8629Xw -0.0034X5 + 0.2333Xv 0.89 NB35A-N + NB45A-N (8) 35-45 28 y ~ =-0.3204 +O. 7506Xw +0.0032X5 + 0.3493Xv 0.74 NB24A-Ja, +NB35A-N; +NB45A-N (9) 24-45 38 y I\ =-0.3542 +0.7911Xw +0.0023Xs + 0.2964Xv 0.79 NBlSA-Ja +NB24A-Ja +NB35A-N ,. +NB3SA-N (10) 15-45 48 y =-0.1453 +0.7899Xw -0~0019Xs + 0.2268Xs 0.77 a Data used from Sununer experiments. See Pilot Project Report. f\.) • Figure 1. Comparison of standard and routine metabolic levels of ' . Cynoscion nebulosus in Nueces Bay and sea waters of various salinities and in summer and autumn. Upper dotted line is for routine· summer metabolic levels in sea waters; lower dotted line for summer standard metabolic levels in sea water. Encircled points are for Nueces Bay waters: at 15-25 ppt for summer • routine (upper) and standard (lower) metabolic levels and for corresponding autumn data at 34-35 and 45 ppt. Autumn fish in relatively poor condition with appreci­able natural weight loss. All data at 28°c, • \ (. . • \ \.",, \ \ 1.) 22 .• • ••.•• . • . • • •. •. •. •• . . • • . • • • • • 0 . \........ • 0 •• • . • • •• • .. 0 U> 0 \ 0 0 ~ ~ 0 0 • . • • ... >­ . . • t­ • . • • 0 .• z 0 •• C\J _J I G) ..:• I ..../ •• <( 0 •.. 0....· CJ) • ... •• •.. -------------~------------.----t~O C\J. 0 Q) N C\J C\J I -~ H 1-~ >t iO ~ ff'I 901 • Table 5. November-December, 1975 data for JI0.1ltiple·regression calculations of spotted seatrout respiratory metabolism rates in relation to selected seawater salinities, fish weightsand lengths, and swimming velocities. Temperature controlled at 2so. Swimm.:Lng Log mg Log mgLog Velocitl Experiment Salinity Length Weight (L sec-) 02 hr-1 02 Kg-1 hr-1 Date Number (ppt) (mm) (g) (cm) 22 XII 75 SW14A 14.0 212 1.8388 .1.07 1. 2180 2.3792 SW14B 14.0 263 2.1173 0.65 . 1.4470 2.3297 24 XII 75 SW14C 14.0 392 2.5803 a.so 1.9704 2.2901 SW14D 14.0 364 2.6284 0.59 1.9784 2.3500 SW14E 14.0 388 2.6794 0.54 2.0090 2.3296 26 XII 75 SW14F 14.0 435 2.8751 0.29 2.0586 2.1835 SW14G 14.0 410 2.7419 0.32 1. 9187 2.1767 29 XII 75 SW14H 14.0 372 2.6866 0.57 1.8814 2.1947 SW14I 14.0 . 408 2.7380 0.57 1.9616 2. 2236 SW14J 14.0 422 2. 7810 0.35 1.8847 2.1048 Means N=lO 14.0 366.6 2.56668 0.545 1.83279 2.25619 16 XII 75 SW18.4A 18.4 271 2.2041 0.74 1. 5390 2.3348 SW18.4B 18.4 198 1.7482 1.05 1. 3284 2.5802 f\) w (Table 5 cont. ) 17 XII 75 SW18.4C 18.4 248 2.1106 0.59 1.3876 2.2770 SW18.4D 18.4 185 1.6435 1.23 1.2079 2.5644 SW18.4E 18.4 238 1. 9823 0.89 1. 2180 2.2357 18 XII 75 SW18.4F 18.4 236 2.0000 0.60 1.4176 2.4176 SW18.4G 18.4 252 2.0864 0.74 1.4263 2.3400 SW18.4H 18.4 254 2.0719 1.04 1.4496 2.3777 SW18.4I 18.4 207 1.8451 0.66 1.2370 2.3919 SW18.4J 18.4 219 1.8808 0.76 1.4346 2.5538 Means N=lO 18.4 230.8 1.95729 0.830 1. 36460 2.40731 25 XII 75 SW22.7A 22.7 305 2.4609 0.79 1.9076 2.4467 SW22.7B 22.7 236 2.0682 0.48 1. 5085 2.4403 SW22.7C 22.7 306 2.4216 0.53 1.8719 2.4503 SW22.7D 22.7 373 2.7076 . o. 74 2.0590 2.3514 11 XII 75 SW23A 23 237 21 0334 0.89 1.4302 2.3968• SW23B 23 226 2.0000 . 0.98 1. 5398 2.5398 SW23C 23 236 2.0000 1.24 1.5156 2.5156 SW23D 23 288 2.2788 1.06 1. 7644 2.4856 I\) J:;:­ SW23E 23 241 2.0755 1.24 1. 5623 2.4867 ~­ (Table 5 cont. ) 12 XII 75 SW23F 23 211 1.8195 0.55 1.2923 2.4727 1.06 1.2774 2.4921 SW23G 23 203 1.7853 1. 2033 2.4709 SW23H 23 194 1.7324 0.78 SW23I 23 418 2.8215 0.48 2.0472 2.2256 I 1· SW23J 23 218 1.9031 ·O .98 1.3701 2.4671 ; I' Means N=l4 22.9 263. 7 2.15056 0.843 ·1. 59640 2.44583 ----------------------------------------------------------------------------------------------I 145 1.3979 0.94 1.0803 2.6823 20 XI 75 SW25A 25 SW25B 25 277 2.3909 o.oo 1.6792 2.2882 353 2.6721 0.47 2.0148 2.3427 SW25C 25 370 2.7202 0.22 2.0321 2.3120 SW25D 25 330 2.5705 0.43 1.9892 2.4187 SW25E 25 SW25F 25 304 2.4409 0.43 1.8396 2.3987 23 XI 75 SW25G 25 310 2.4969 0.90 1.9064 2.4095 SW25H 25 312 2.4594 0.60 1.8824 2.4230 SW25I 25 372 2.6866 0.65 2.0269 2.3402 24 XI 75 SW25J 25 318 2.5119 0.91 1.9202 2.4083 f\) \.n (Table 5 cont. ) SW25K 25 325 2.5647 1.02 1.9948 2.4301 SW25L 25 315 2.4942 1.05 1.8434 2.3493 Means N=l2 25 310.9 2.45052 0.635 1.85078 2.40025 f\) °' Table 6. January-February, 1976 data for multiple regression calculations of spotted seatrout respiratory metabolism rates in relation to selected salinities of sea water (SW), fish weights and lengths, and swirruning velocities. Temperature controlled at 15oc. Swirruning Log mg Log mg Log Velocitl Experiment Salinity Length Weight (L sec-) o2 hr-1 o2 Kg-l hr-1 Date Number (ppt) (rrun) (g) (cm) 9 I 76 SWA14.2A 14.2 401 2. 7419. 0.66 1.8671 2.1252 SWA14.2B 14.2 403 ·2. 7427 o. 76 1. 9894 2. 2467 SWA14.2C 14.2 382 2.6830 0.63 1.8556 2.1726 SWA14.2D 14.2 406 2.7574 0.59 1.9922 2.2348 SWA14.2E .14.2 403 2.7664 0.21 1.8399 2.0735 SWA14.2F 14.2 370 2.6243 0.60 1.8513 2.2270 SWA14.2G 14.2 397 2.7243 0.45 1.9401 2.2158 SWA14.2H 14.2 405 2. 776 7 o.oo 1.8456 2.0689 SWA14.2I 14.2 400 2.7924 0.28 2.0237 2.2313 Means 14.20 396. 3 2.73434 0.464 1.91166 2.17731 21 I 76 SWA17.2A 17.2 248 2.1335 0.94 1. 2455 2.1120 SWA17.2B 17.2 332 2.5315 0.00 1. 5935 2.0620 SWA17.2C 17.2 259 2.1703 0.78 1.4691 2.2988 SWA17.2D 17.2 284 2.2455 1.40 1.6497 2.4042 I\) -.J 23 I 76 SWA17.2E SWA17.2F SWA17.2G SWA17.2H SWA17.2I SWA17.2J Means 27 I 76 SWA22.7A SWA22.7B SWA22.7C SWA22. 7D SWA22.7E 29 I 76 SWA22.7F SWA22.7G SWA22.7H 30 I 76 SWA22.7I SWA22.7J Means 17.2 17.2 17.2 17.2 17.2 17.2 17.20 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.7 22.70 (Table 6 cont. ) 390 2.7016 255 2.1461 349 2.5809 371 2.6222 254 2.0934 226 1.9191 296.8 2.31441 268 2.1931 273 2.2330 335 2.4728 304 2. 3626 246 2.0755 393 2.7039 218 1.9345 210 1.8692 236 2.0374 269 2.1931 275.2 2.20761 0.31 0.53 0.63 0.39 1.15 1.24 0.737 1.26 1.29 1.09 1.27 1.52 0.52 1.15 1.07 0.93 0.82 1.092 1.5435 1.4029 1.6253 1.6283 1.0881 1. 2982 1.45441 1.6063 1.4595 1. 5637 1.6146 1.4794 1.9721 1.1915 1.1326 1.2728 1.4019 1.46944 1.8419 2.2568 2.0444 2.0061 1.9947 2.3791 2.14000 2.4132 2. 2265 2.0909 2.2510 2.4039 2. 2682 2.2570 2. 2634 2.2354 2.2088 2.26183 F\) (X) •' ----­ (Table 6 cont.) 23.9 122 1.0792 1.86 0.4249 2.3457 2 II 76 SWA23.9A 1.07 0.4270 2.2509 SWA23.9B 23.9 127 1.1761 2-. 3449 3 II 76 SWA23.9C 23.9 117 1.0170 0.66 0. 3619 0.6730 2.6763 SWA23.9D 23.9 139 12967 1.04 Means 23.90 126.3 1.14225 1.158 0.47170 2.32945 23 II 76 SWA24.7A 24.7 297 2.3284 0.84 1.4519 2.1235 SWA24.7B 24.7 302 2.3424 0.89 1.6742 2.3318 24.7 360 2.5866 0.46 1.8032 2.2166 SWA24.7C SWA24.7D ·24.7 269 2.2148 0.82 1.4793 2. 2645 SWA24.7E 24.7 257 2.1335 1.00 1.0821 1.9486 24 II 76 SWA24.7F 24.7 285 2.2480 0.56 1.4325 2.1845 2. 0605 SWA24.7G 24.7 279 2.2253 0.73 1.2858 Means 24.70 292.7 2.29700 0.757 1.45843 2.16657 f\) \0 Table 7. Multiple regression equations for oxygen consumption rates of Cynoscion nebulosus in sea waters at selected salinities and at 25oc and 15°c. Winter data. . Expected Experiment Salinities Log mg. Numbers (ppt) N o2hr-l Constant At 25°c (November-December): SW14A-J ,,, +SW18.4A-J (11) 14-18.4 20 y = -0.2238 SW18.4A-J A +SW23A-J (12) 18.4-23 24 y = -0.6150 SW23A-J A +SW25A-L (13) 22.7-25 26 y = -0.4974 ,,.. All salinities(l4) 14-25 46 y = -0.5196 At 15°C (January-February): SWA14.2A-I +SWA17.2A-J (15) 14.2-17.2 19 y A = 1. 0854 SWA17.2A-J +SWA22.7A-J (16) 17.2-22.7 20 y" = -0.6825 SWA22.7A-J I\ +SWA24.7A-J (17) 22.7-24.7 20* y = ~0.1734 ,.. All salinities(l8) 14.2-24.7 40 y = -0~6118 *One aberrant value deleted. Log Wt., Xw (g) +0.7957Xw +0.8179Xw +0.8198Xw +0.8356Xw +0.6516Xw +0.8024Xw +0.9148Xw +0.9037Xw Salinity, Xs (ppt) -0.0031X5 +0.0155X5 +0.0112Xs +0.0102Xs -0.0707Xs +0.0108X5 -0.0189X5 -0.0036Xs Velocity, ~ Lengths (cm (L sec-1) +0.1070Xv +0.1147Xy +0.0907Xv +0.0974Xv +0.1058Xv +0.1282Xv +0.0466~ +0.1332Xy Multiple Correlation R 0.97 0.96 0.99 0.98 0.93 0.84 0.98 0.96 w a P<0.05 for all but equations 16 and 17; the negative bv in 17 is • possibly caused by pectoral rowing and non-locomotory (sponta­neous) activity of slower swimming fish at high energy cost, while the faster swimmers utilize less energy costly caudal pro­pulsion. Table 7a is a collection of multiple regressions across the autumn 25°c and the winter 15°C temperature levels to allow for the calculation of the temperature coefficient bt over the entire, but small, salinity ranges in equations 19 and 20. The salinity coefficient (e.g. 21) in the combined data is not significantly different from zero (P~O.l); all other bw, bt and bv are signifi­cantly different from zero at least at P<0.05, and mostly at considerably lower probabilities. The standard levels of log 02 kg-l hr-1 for each salinity • group of both 15°C and 25°c data (as extrapolated back to bv = 0 from the lowest point in each group) and the corresponding average routine levels are plotted in the top panel of Fig. 2. The bottom panel contains .the plots of routine scope at 15° and 25°c. San Antonio Bay Late Winter Data The San Antonio Bay (SAB) waters at an ambient salinity of about 10.9 ppt and a temperature of about 15°C ~ere initially utilized for the respiratory metabolic determinations. To account for any very low temperatures during occasional years when coastal water temperatures can drop to l0°c or less, lo0 c series were run at 10.9 ppt and at 20.0 ppt. A series at 15° and 20.0 ppt was run to eva~uate salinities higher than those usually found in San • Antonio Bay. Results of these four series. are in Table 8. Table 7a. Same as Table 7, but including partial regression coefficients, ht, for temperature, Xt, over low, high and total salinity ranges. Expected Log Wt. Temp., Salinity, Velocity Multiple Correlation Experiment Temps. Salinities Log ml x Xt Xs Xv Numbers (OC) (ppt) N o2hr-Constant (~) (OC) (ppt) (L sec-1) R SW14A-J +SW18.4A-J +SWA14.2A-I 39 y I\ -0.8154 +0.8736Xw +0.0136Xt + •••••• +0.1435Xv 0.93 +SWA17.2A-J (19) 15-25 14.0-18.4 = SW22.7A-D +SW23A-J +SW25A-L +SWA22.7A-J +SWA23.9A-D y +0.8797Xw +O.Q231Xt +.••••• +0.0926Xv 0.98 +SWA24.7A-G (20) 15-25 22.7-25.0 47 ~ = -0.9457 ,.. All of above (21) 15-25 14.0-25.0 86 y = -1.0141 +0.8937Xw +0.0190Xt +0.0041X5 +0.1164Xv 0.97 w f\) • • Figure 2. Late autumn (25°c) and winter (15°c) metabolic data for Cynoscion nebulosus over restricted salinity range in sea Wate~s. Encircled points and solid lines for November-December data at 25°c;· points in triangles and dashed lines for January-February data at 15°C. In top panel the upper line of each of the paired visually drawn solid or dashed lines represents the routine metabolic levels; the lower of the visually drawn paired lines represents standard metabolism. In lower panel the scope is plotted for 25° and 15° data to show optimal salinity response at about 20 ppt • • 2.6 I 2.4 a: ::i: I (.!) 2.2 -&-------£__ G 2.0 I. 8 ' L!l,.__ --­ ' '~ --, ROUTINE SC 0 p E. 120 I a:: :c (!) I 00 -·--, I ~ ,,, .... ---.... ~ 0 (\J 80 / \ / ' / t!) / p '' :2 / •/ \60 / \/ \ / \ 40 I \ ~ • 20 12 16 20 SALINITY -0/oo UBRARY AT AUST\N OF TEXAS --VERSITY ' ' JI EUN1 r E H<; : . i i_ ~ £ SCl£N.... .. ,"l ·' : 111 MAR\N .. ,.. t. c HY. A.S. .'J ' .. I Table 8. San Antonio Bay (SAB) data for multiple regression calculations of Cynoscion nebulosus respir~tory metabolism rates in relation to selected salinities, temperatures, fish weights and lengths, and swirruning velocities. February-March, 1976. Swirruning Log Velocitl Log mg Log mg Experiment Temp. Salinity Length Weight (L sec-) Date Number (OC) (ppt) (rrun) (g) (cm) o2hr-l o2kg-lhr-1 27 II 76 SABlA 15.0 10.9 251 2.1492 0.47 1. 3649 2.2157 SABlB 15.0 10.9 288 2.3222 0.63 1.4370 2.1148 SABlC 15.0 10.9 260 2.2041 1.14 1. 5163 2.3122 • 1 III 76 SABID 15.0 10.9 . 368 2.6395 0.51 1.8329 2.1934 SABlE 15.0 10.9 245 2.0969 1.44 1.4181 2.3212 SABlF 15.0 10.9 387 2.6693 0.92 2.0055 2.3362 SABlG 15.0 10.9 265 2.2227 1.31 1. 5570 2.3343 2 III 76 SABlH 15.0 10.9 245 2.0934 0.34 1.2842 2.1908 SABlI .15.0 10.9 243 2.1038 0.67 1.1284 2.0246 SABlJ 15.0 10.9 280 2.2504 0.72 1.2041 1.9534 Means 15.0 10.90 283.2 2.27515 0.815 1.47484 2.19966 9 III 76 SAB2A 10.0 10.9 . 224 1.9138 0.51 0.6096 1.6958 SAB2B 10.0 10.9 . 292 2.3010 0.49 1.0722 1.7712 SAB2C 10.0 10.9 278 2.2833 0.75 1.3672 2.0839 w \.J1 (Table 8 cont.) SAB2D 10.0 10.9 317 2.4362 0.64 1.3655 1.9293 SAB2E 10.0 10.9 360 2.5843 0.70 1.5880 2.0037 10 III 76 SAB2F 10.0 10.9 262 2.1523 0.68 . 1.1149 1.9626 SAB2G 10.0 10.9 376 2.6435 0.51 1.6848 2.0413 SAB2H 10.0 10.9 245 2.1038 0.58 1.1186 2.0148 Means 10.0 10.90 294.3 2.30228 0.615 1.24010 1.93783 11 III 76 SAB3A 10.0 20.0 343 2. 5635 0.32 1.5339 1.9704 SAB3B 10.0 20.0 375 2.6884 o.oo 1. 5301 1.8417 SAB3C 10.0 20.0 408 2.8116 0.22 1.6245 1.8129 SAB3D 10.0 20.0 399 2.7482 0.27 1. 7260 1.9778 SAB3E 10.0 20.0 363 2.6571 0.47 1. 5971 1.9400 12 III 76 SAB3F 10.0 20.0 413 2.7987 o.oo 1.6461 1.8474 SAB3G 10.0 20.0 400 2.8055 0.24 1..6637 1.8582 13 III 76 SAB3H 10.0 20.0 424 . 2.8209 0.52 1.8476 2. 0267 SAB3I 10.0 20.0 249 2.1492 1. 35 1.3359 2.1867 SAB3J 10.0 20.0 340 2.5453 o. 39 1. 5423 1.9970 Means 10.0 20.00 371.4 2.65884 0.378 1.60472 1.94588 29 III 76 SAB4A 15.0 20.0 378 2.7126 0.76 1. 7892 2.0766 w SAB4B 15.0 20.0 . 360 2.6232 0.75 1. 5724 1.9492 0\ (Table 8 cont.) 2.4150 0.21 1.5967 2.1817 30 III 76 SAB4C 15.0 20.0 298 430 2. 9365 0.21 1.9810 2.0445 SAB4E 15.0 20.0 31 III 76 SAB4F 15.0 20.0 354 2.5185 0.23 1.6004 2.0819 2.5944 0.45 1.7922 2.1978 SAB4G 15.0 20.0 354 415 2.8426 0.45 2.0055 2.1629 SAB4H 15.0 20.0 ~ 20.0 276 2.3010 0.63 1.6369 2.3359 SAB4I 15.0 2. 2693 2.0792 0.58 1.3485 SAB4J ·15.0 20.0 245 1.70253 2.14442 345.6 2.55811 0.419 Means 15.0 20.0 • w ........;J 38 ·• Multiple regression equations for various salinity combi­ • nations are in Table 9. In an attempt to evaluate effects of deleting some of the more disparate measurements, the calculated " • Y values were compared to the observed Y. When the differences ,.. between Y and Y were beyond 2 standard deviations, the regressions were recalculated after deletion of these values, as indicated for the alternative equations in Table 9. While these deletions only slightly "improved" an overall regression and the individual partial coefficient, there usually was little biological reason for the deletions. In any case, all the multiple regressions were highly significant at P<<0.001; all the bw at P<0.001; bs all non-significant; all bt at P<0.001, except (24) with P<0.005; and the bv at P<0.05 to P<0.001. Lavaca Bay Spring· Data The April waters from Lavaca Bay had an ambient salinity of about 19.0 ppt and a temperature of about 15°C, which were the initial conditions for experimentation. Other experimental sets included tempe~ature-salinity regimes of 25°c and 20 ppt, 24°c and 30 ppt, and 15°C and 30 ppt. The results are in Table 10. Regression statistics for various combinations of temperature and salinity levels are in Table 11 along with alternative equa­tions with successive deletions when the observed Y exceeded the ,.. Y by 2 or more standard deviations. Here the purpose of the deletions was .to determine empirically whether the several statis­tically non-significant and negative bv could be altered to positive values, since the Xv were highly variable in relation to the small • range of swimming activity~ much of which evidently was non­locomotory. Since none· of the bv were significant and since the Table 9. Multiple regression equations for oxygen consumption rates of Cynoscion nebulosus in San Antonio Bay (SAB) water at ioo-15oc and at 10.9 (ambient) and 15.0 ppt. salinity. Equations "modified" by deletions of aberrant data denoted as 22a, etc. Experiment Expected Log Wt. Temp. Salinity Velocity Multiple Correlation Numbers and Temps. Salinities Log ml Xw Xt Xs Xv ( L sec-1) R (Eq. Deletions (oC) (ppt) N 02hr-Constant (g) (OC) (ppt) SABlA-J 15.0 10.9-15.0 19 I\ y -0.8595 +O. 9226Xw + •.• +0.0056Xs + 0.2134Xv 0.92 (22 +SAB4A-J = 18 y .I\ -0.7632 +O. 9128Xw + ••• +0.0024X8 + 0.1970Xv 0.94 (22 -SABlJ = SAB2A-H . +SAB3A-J 10.0 10.9-20.0 18 y I\ = -1.8406 +1. 2266Xw +••• +0.0020X8 + 0.3826Xv 0.97 (23 17 y"' -1. 3819 +1.0551Xw + ••• +0.0034Xs + 0.3023Xv 0.96 (23 -SAB2A = , .,.:\ .. SABlA-J y"' + 0.2444Xv 0.95 ( 24 +SAB2A-H 10.0-15.0 10.9 18 = -2.1764 +l.2283Xw +0.0438Xt + ••• • -SABlJ -SAB2A 16 y ~ = -1.8820 +l.1191Xw +0.0441Xt + ••• + 0.2128Xv 0.95 SAB3A-J /\ y +0.7855Xw +0.0339Xt +~ •• +0.1786Xv 0.93 (25 +SAB4A-J 10.0-15.0 20.0 19 = -0.8906 "' -SAB4B 18 y = -0.9184 +0.7836Xw +0.0379Xt + ••• +0.1601Xv 0.95 (25 All data 10.0-15.0 10.9-20.0 37 y .I\ = -1. 7437 +l.0284Xw +0.0400Xt +O.OOSSXs +0.2626Xv 0.94 (26 -SABlJ ,. -SAB2A -SAB4B 34 y = -1.4938 +0.9464Xw +0.0410Xt +0.0045Xs +0.2165Xv 0.95 ( 26 w \0 Table 10. Spring data for multiple regression calculations of Cynoscion nebulosus respiratorymetabolism rates in relation to selected salinities of Lavaca Bay (LB) waters,temperatures, fish weights and lengths, and swimming velocities. Swimming Log mg Log mgLog Velocitl Experiment Temp. Salinity Length Weight (L sec-) o2 hr-1 o2 Kg-1 hr-lDate Number (OC) . (ppt) (mm) (g) (cm) 6 IV 76 LBJA 15.0 19.0 269 2.1703 0.83 0.9854 1.8151 LBlB 15.0 19.0 355 2. 556 3 0.64 1.7820 2.2257 LBlC 15.0 19.0 323 2.4594 0.43 1.3377 1.8783 LBlD 15.0 19.0 408 2. 7634 0.35 1.9436 2.1802 LBlE 15.0 19.0 375 2 .6435 0.66 1.7029 2.0594 8 IV 76 LBlF 15.0 19.0 396 2.6335 0.37 1.8228 2.1893 LBlG 15.0 19.0 443 2.9395 0.40 2. 0604 2.1209 • LBlH 15.0 19.0 405 2.8102 0.41 1.9644 2.1542 9 IV 76 LBlI 15.0 19.0 375 2. 7634 a.so 1.9674 2.2040 LBlJ 15.0 19.0 324 2. 5263 0.40 l.6990 2.1360 Means 15.00 19.00 372.3 2.62658 0.499 1.72656 2.09631 12 r.v 76 LB2A 25.0 20.0 378 2.6928 o. 36 2.0154 2.3226 LB2B 25.0 20.0 380 2.7135 0.49 1.9111 2.1976 LB2C 25.0 20.0 408 2.7973 0.39 2.0469 2.2496 t 0 (Table 10 cont. ) LB2D 25.0 20.0 367 2.6464 0.44 1.9599 2.3135 LB2E 25.0 20.0 361 2.6031 0.40 1.9392 2. 3361 13 IV 76 LB2F 25.0 20.0 296 2. 3655 0.54 1.8821 2. 5166 LB2G 25.0 20.0 367 2.6628 0.28 1.9539 2.2911 LB2H 25.0 20.0 260 2.1461 0.46 1.6486 2.5025 LB2I 25.0 20.0 262 2.1367 0.58 1.4894 2.3527 LB2J 25.0 20.0 264 2.1523 0.56 1.6443 2.4920 Means 25.00 20.00 334.3 2.49165 0.450 1.84908 2.35743 16 IV 76 LB3A 24.0 30.0 396 2.7709 0.57 2.0696 2.2987 LB3B 24.0 30.0 352 2.6075 0.52 1.8535 2.2460 LB3C 24.0 30.0 356 2.6212 0.52 1.9235 2.3023 • 19 IV 76 LB3D 24.0 30.0 343 2.5490 0.52 1.7972 2.2481 LB3E 24.0 30.0 292 2.2945 0.58 1.6495 2.3550 20 IV 76 LB3F 24.0 30.0 236 2.0334 1.12 1.3334 2.3000 21 IV 76 LB3G 24.0 30.0 384 2.7185 o.oo 1.8120 2.0935 LB3H 24.0 30.0 301 2.3766 0.57 1.8193 2.4427 LB3I 24.0 30.0 388 2.6998 0.44 ·2. 0932 2.3934 Means 24.00 30.00 338.7 2.51904 0.538 1.81680 2.29776 .t::­ ...... (Table 10 cont. ) 26 IV 76 LB4A 15.0 30.0 297 2.3909 0.29 1. 2826 1.8917 LB4B 15.0 30.0 372 2.6513 0.55 1.7116 2.0603 27 IV 76 LB4C 15.0 30.0 378 2.6721 0.49 1.6702 1.9981 LB4D 15.0 30.0 317 2.4533 0.52 1.6406 2.1873 LB4E 15.0 30.0 416 2.-8325 0.37 1.9566 2.1241 ·. LB4F 15.0 30.0 412 2.7952 0.32 2.0567 2. 2615 29 IV 76 LB4G 15.0 30.0 390 2.7024 o. 36 1.9526 2.2502 LB4H 15.0 30.0 423 2.8248 0.14 1.8344 2.0096 LB4I 15.0 30.0 327 2.5315 0.22 1.6547 2.1232 LB4J 15.0 30.0 410 2.8169 0.49 1.8294 2.0125 Means 15.00 30.00 374.2 2.66719 0.375 1.75894 2.09185 • ..i::­1\) Table 11. Multiple regression equations for oxygen consumption rates of Cynoscion nebulosus in Lavaca Bay (LB) waters at selected salin~ties and temperatures. April data. Equations "modified" by deletions of aberrant data denoted as 27a, etc. Experiment Expected Log Wt. Temp. Salinity Velocity MultipleNumbers and Temp. Salinity Log m~ Xw Xt Xs Xv Correlation Deletions (OC) (ppt) N o2hr-. Constant (g) (OC) (ppt) (L sec-1) (Eq.) LBlA-J +LB4A-J 15.0 19.0-30.0 20 ;. y = -1. 2544 .+1.1883Xw + .•• -0.0032X5 -0.1586Xv 0.85 (27) -LBlA, C, G I' -LB4A, F, G 14 Y= +0.3949 +0.6827X w + ••• -0.0129Xs -0.2075Xv 0.82 (27a) -LBlA, C, F, G -LB4A, F, G -LBlA,C,E,F,G -LB4A,F,G LB2A-G +LB3A-I -LB2B -LB3G, H -LB2B, F -LB3G, H, I A 13 Y= +l. 9917 +O. 7614Xw +••• -0.0090Xs -0.0876Xv 0.90 (27b) ·12 /'-y = -0.0086 +0.7711~ + .•• -0.0103X+ 0.0124Xv 0.93 ( 27c ), 5 /\ 24~0~25.0 20.0-30.0 19 Y= +O. 0496 +O. 7620~ +••• -0.0055Xs + 0.0258Xv 0.91 • ( 28) /\ 16 Y= +o. 2367 +O. 7075Xw +••• -0.0017X5 -0.2364Xv 0.96 (28a) /\ 14 Y= +0.2197 +o. 7076~ +••• -0.0021X5 -0.2191Xv 0.98 (28b) ...t::" w • LBlA-J +LB2A-J 15.0-25.0 19.0-20.0 20 -LBlA,C,G -LB2B 16 -LBlA,C,F,G -LB2B 15 -LBlA,C,F,G -LB2B,F,I 13 LB3A-I +LB4A-J 15.0-24.0 30.0 19 -LB3G-H -LB4A,F,G 14 All data 39 -LBlA, C~ G -LB2B -LB3G, H -LB4A,F,G 30 -LBlA, C, F, G -LB2B -LB3G,H,I -LB4A,F,G 28 (Table 11. cont.) ,.. Y= -0.1856 +0.7216Xw +0.0193Xt + ••• -0.5468X 0.85 < 29) v ,.. y =. +0.3005 +0.6069Xw +0.0081Xt + ••• -0.3544Xv 0.89 (29a : ,,.. Y= -0.1596 +0.6927Xw +0.0139Xt +.•• -0.1212Xv 0.93 (29b ,.... y = +0.0283 +0.6371Xw +0.0125Xt + ••• -0.1595X 0.96 (29c v /'Y= -1. 5153 +l.0838Xw +0.0208Xt + ••• +0.1913~ 0.89 ( 30) " Y= -0.8537 +0.8466Xw +0.0257Xt + ••• -0.1156Xv 0.96 (30a /' (31) Y= -1.0104 +0.9260Xw +0.0236~ -0.0018X -0.0189~ 0.85 5 " Y= -0. 2656 +0.7658Xw +0.0174Xt -0.0076X5 -0.0995Xv 0.91 (3la /\ Y= -0.3130 +0.7621Xw +0.0181Xt -0.0070X5 -0.0683Xv 0.95 (31b .r::::­.r::::­ (Table 11. cont.) -LBlA, C, F,G -LB2B, F -LB3G, H, I "" -LB4A,F,G 27 y = -0.3517 +0.7740Xw +0.0175Xt ~o.0064X5 -0.0667Xv 0.96 • ( 3lc) .t::­ Ul bv negative tendency could not be removed by manipulation, the • value bv = 0.15 was arbitrarily used to extrapolate from the lowest Y kg-1 and Xv data point to estimate the standard level for each of the data sets. Interestingly, all the bw were significant at less than P<0.001 except for Eq. 29 (P<0.005). For salinity co­efficients significance at P<0.05 was evident for Eqs. 27a, b, c, 28, and 3la, b, c. The bt were all significant at P<0.025 or less, except for Eq. 29a. Nueces Bay Spring and Summer Data • In Table 12 are the results for the data sets: 15°C and 32 ppt, 24°c and 32 ppt, 15°C and 20 ppt, 25°c and 20 ppt, and 15°c and 10 ppt. Note that the dates do not necessarily corre­spend to seasonally changing temperatures and salinities. At the low temperature and salinity levels of July, two com~tose fish were apparently ill-adapted to these levels and were omitted from further calculations. The multiple regressions are in Table 13. After some of the more biologically obvious discrepant values were deleted, alternative regression calculations were made, but the extended elimination of data, as in the previous section, was dispensed with. All the bw and bt coefficients are statistically signifi­cant at P<0.001; none of the bs is significant; all the bv are· significant at P<0.025 or less, except for bv in Eqs. 33, 33a, 35, which are not significant . • fish weights and lengths, and swimming velocities. Table 12. May-July, 1976 Nueces Bay (NB) data for multiple regression calculations of Cynoscion nebulosus respiratory metabolism rates in relation to selected salinities, temperatures, Swimming Log mg Log mg Date Experiment Number Temp. (OC) Salinity (ppt) Length (mm) Log Weight (g) Velocitl (L sec­) (cm) o2 hr-1 02 Kg-1 hr-1 5 v 76 NB5A 15.0 32.0 291 2.3096 0.28 1.4087 2.0991 NB5B 15.0 32.0 364 2.6232 0.24 1. 7231 2.0999 NB5C 15.0 32.0 305 2. 3655 0.29 1.1798 1.8143 NB5D 15.0 32.0 420 2.7404 0.42 1.8461 1.7457 NB5E 15.0 32.0 209 1.8573 0.85 0.8306 1.9733 7 v 76 NB5F 15.0 32.0 407 2.8222 0.27 1.6110 1.7888 NB5G 15.0 32.0 320 2. 526 3 0.77 1.6347 2.1084 NB5H 15.0 32.0 287 2.3385 0.46 1.2133 1.8748 NBS! 15.0 32.0 343 2.5866 0.63 1.7451 2.1585 Means 15.00 32.00 327.3 2.46329 0.468 1. 46582 1.96253 10 v 76 NB6A 24.0 32.0 344 2.5198 0.53 1.8020 2.2822 NB6B 24.0 32.0 342 2.5051 0.52 1.8024 2.2973 NB6C 24.0 32.0 344 2.5658 0.82 1.8681 2.3023 NB6D 24.0 32.0 280 2.2742 0.64 1.6322 2.3580 J:: (Table 12 cont.) NB6E 24.0 32.0 343 2.5623 0.75 1.9563 2.3940 12 v 76 NB6F 24.0 32.0 328 2.4843 0.41 1.7459 2. 2616 NB6G 24.0 32.0 310 2.4249 0.33 1.6496 2.2247 NB6H 24.0 32.0 434 2.7505 0.22 1.8605 2.1100 NB6I 24.0 32.0 396 2.7210 0.79 2.0111 2.2901 . NB6J 24.0 32.0 315 2.4409 1.00 1.9282 2.4873 Means 24.00 32.00 J 343.6 2.52488 0.601 1.82563 2.30075 25 v 76 NB7A 15.0 20.0 350 2.5625 0.46 1.4393 1.8758 28 v 76 NB7B 15.0 . 20.0 351 2.5599 0.54 1.6231 2. 0632 NB7C 15.0 20.0 369 2.6149 0.44 1.6386 2.0237 NB7D 15.0 20.0 359 2.6075 0.59 1.4984 1.8835 NB7E . 15.0 20.0 394 2.7490 0.73 1.8952 2.1462 NB7F 15.0 . 20.0 378 2.7160 0.66 1.7575 2.0415 31 v 76 NB7G 15.0 20.0 434 2.8274 0.31 1.9837 2.1563 NB7H 15.0 20.0 320 2.4594 0.30 1.8395 2.3801 NB7I 15.0 20.0 400 2.7993 0.23 1.5323 1.7335 Means 15.00 20.00 372.8 2.65521 0.473 1.68979 2.03376 .i:::­ CX> (Table 12 cont.) 11 VI 76 NB8A 25.0 20.0 345 2.5514 0.33 1.8087 2.2573 NB8B 25.0 20.0 326 2.4378 0.55 1. 5822 2.1444 NB8C 25.0 20.0 230 2.0086 0.69 1. 3664 2.3578 NB8D 25.0 20.0 412 2.8325 o. 38 2.2239 2.3914 NB8E 25.0 20.0 312 2.3802 0.75 1.7329 2.3527 21 VI 76 NB8F 25.0 20.0 251 2.1335 0.68 1.5135 2.3800 NB8G 25.0 20.0 269 2.2201 0.71 1. 5113 2.2912 NB8H 25.0 20.0 315 2.4654 0 .67 1.8195 2.3541 NB8I 25.0 20.0 273 2.2148 .0. 78 1.6332 2.4184 NB8J 25.0 20.0 308 2. 3655 0.71 1. 7210 2.3555 Means 25.00 20.00 304.1 2.36098 0.625 1.69126 2.33028 23 VI 76 NB9A 25.0 10.0 290 2.3181 0.60 1. 5022 2.1841 NB9B 25.0 10.0 312 2.4654 O·. 53 1.8030 2.3376 NB9C 25.0 10.0 346 2.5465 0.83 1.9292 2.3827 24 VI 76 NB9D 25.0 10.0 316 2.4281 0.79 1. 7088 2.2807 NB9E 25.0 10.0 270 2.2553 0.76 1. 5230 2.2677 NB9F 25.0 . 10.0 288 2.2923 0.88 1.7204 2.4281 NB9G 25.0 10.0 279 2.3054 0.93 1.7151 2.4097 ~ \0 (Table 12 cont.) NB9H 25.0 10.0 297 2.3139 1.01 1.8315 2. 5176 25 VI 76 NB9I 25.0 10.0 352 2. 5611 0.56 1.9535 2.3924 NB9J 25.0 10.0 274 2.2504 0.93 1.7354 2.4850 Means 25.00 10.00 302.4 2. 37365 0.782 1.74221 2. 36856 28 VI 76 NBlOA . 15 .o 10.0 348 2.5752 0.64 1.6299 2.0547 1. 3214 2.0247 NBlOB 15.0 10.0 279 2. 296 7 0.81 NBlOC 15.0 10.0 292 2.3096 0.55 1.4730 2.1634 NBlOD 15.0 10.0 251 2.1335 0.37 0.9112 1.7777 7 VII 76 NBl9S-----l5r9--------l9r9--------29l-------2r3592--------9r99-----9r3434------9.9932-* NBlOF 15.0 10.0 270 2.2742 0.27 1.0881 1.8139 8 VII 76 NBlOG 15.0 10.0 259 2.1271 0.42 1.0137 1.8866 296 2.3096 0.73 1.3813 2.0717 NBlOH 15.0 10.0 NBlOI 15.0 10.0 304 2.4082 0.32 1.2858 1.8776 9 VII 76 NB1SJ-----l5r9--------l9r9--------21S-------2r294l--------9r34-----9r1l34------l•5993-* Means 15.00 10.00 287.4 2.30426 0.514 1. 26305 1 .. 95879 *Comatose fish. Data deleted. V10 Table 13. Multiple regression equations for oxygen consumption rates of Cynoscion nebulosus in Nueces Bay (NB) waters at selected salinities and temperatures. May-July data. Experiment Expected Log Wt. Temp. Salinity Velocity Multiple Numbers Temp. Salinity Log m~ Xw x Xs ~ Correlation (oC) (ppt) N o2hr-Constant (g) (be) (ppt) (L sec-1 ) (Eq.) NBSA-I "' . +NB6A-J . 15.0-24.0 32.0 19 Y= -1. 7426 +l.0734Xw +0.0281Xt +••• +0.3044Xv 0.95 ( 32) NB7A-I "' +NB8A-J 15.0-25.0 20.0 19 Y= -2.1369 +l.1741Xw +0.0337Xt + ••• +0.3413~ 0.88 (33) -NB7G,I A -NB8B 15.0-25.0 20.0 16 Y= -2.0356 +l.1461Xw +0.0358Xt +••• +0.2328Xv 0.95 (33a) NB9A-J ,.. +NBlOA-I 15.0-25.0 10.0 18 Y= -2.3031 +l.2697Xw +0.0261Xt +~ •• +0.4833Xv 0.97 (34) NBSA-I ,.. +NB7A-I 15.0 20.0-32.0 18 Y= -1. 7924 +l. 2062Xw +••• +0.0004Xs +0.3129Xv 0.90 (35) NB6A-J -A +NB8A-J 24.0-25.0 20.0-32.0 20 Y= -0.8284 +1. ooosxw +••• -0.0018X+0.3106Xv 0.95 ( 36) 5 .I\ -NB8B,D 24.0-25.0 20.0-32.0 18 Y= -0.5878 +O. 8767Xw +••• +0.0003Xs +0.3155Xv 0.97 ( 36a) NB8A-J +NB9A-J 25.0 10.0-20.0 20 v= -1.4165 + l_-176 4Xw + ••• +0.0031X5 +0.4286~ 0.93 (37) -NB8B ,.. -NB9D 25.0 10.0-20.0 18 Y= -1.4769 +1.2061~ +••• +0.0038Xs +0.4215~ 0.96 (37a) \J1 I-' (Table 13. cont.) NB5A-I +NB6A-J +NB7A-I +NBBA-J 15.0-25.0 20.0-32.0 38 " Y= -1. 8288 +l.0854Xw +0.0299Xt +0.0007X5 +0.3006Xv 0.92 ( 38) -NB5A,B,F -NB7G,I " -NBBB 15.0-25.0 20.0-32.0 32 Y= -2. 0166 _:_l.1493Xw +O. 0325Xt -0. 0011X +O. 3403Xv 0. 97 (38a) 5 NB7A-I +NBBA-J +NB9A-J A +NBlOA-I 15.0-25.0 10.0-20.0 37 Y= -2.1506. +l.1807Xw +0.0310Xt +0.0009X5 +0.4053Xv 0.95 (39) -NB7D,G,I -NBBB A -NBlOC 15.0-25.0 10.0-20.0 32 Y= -2. 2696 +1.2034~ +0.0326Xt +0.0038X5 +0.3516Xv 0.98 (39a) A All data 15.0-25.0 10.0-32.0 56 Y= -1. 9837 +l.1305Xw +0.0299Xt +0.0010X+0.3625Xv 0.94 (40) 5 -NB5A,B,F -NB7G -NBBB A. -NBlOC 15.0-25.0 10.0-32.0 so Y= -2.1510 +l.1612Xw +0.0328Xt +0.0010X5 +0.4047Xv 0.97 (40a) Vl I\.) • Maximum Sustained Swinuning Velocity -Blazka Respiration Experiments These 2a0 c experiments included fish from July-August, and from September-October, 1976 as an extension of the pilot project one year earlier. By subsets at 5 ppt intervals and without subset averages, the data for 10 to 45 ppt are assembled in Table 14. (Since many of the fish were intentionally run at minimum and maximum~' averages are not useful.) In addition to Xv, the Xv x -y/""L , where L is the total fish length in cm, are tabulated; In Table 15 are the multiple regressions calculated for adjacent 5 ppt salinity intervals. Not only are the overall regressions, 41-44, very highly significant, the bw and bv are • significant at levels far less than P<0.001. Only the bs in Eq. 44 is significant at P<0.05. To determine any effects that the Xv might have on the other variables, Eq. 41 was recalculated by replacing the Xv with Xss swimming speeds in cm sec-l (not tabulated). This equation is: y ~ = -0.5943 + 1~0363 Xw -0.0057 ' Xs + 0.0043XSS' with R = 0.95 and with bw and bss significant at much less than P<0.001, but with non-significant bss· For the purpose of identifying individual fish data at maximum sustained swimming levels the superscript "l" is used in Table 14. For identifying the fish at resting (Xv = 0) levels, the superscript "2" is used in Table 14. By using only the aver­ages of the maximum log oxygen consumption rate kg-1 hr-1 (Y kg-1 • hr-l) at each salinity a fourth-order relationship between Ykg-1 hr-1 and salinity Xs in a quartic linear form (rounded to 4 significant digits) is: Table 14. Seawater data from Blazka chamber experiments on Cynoscion nebulosus 20°c respiratory metabolism rates in relation to selected salinities, fish weights and lengths, and swimming velocities. July-Aug. 1976. 11/2 y Xs L Xw Xv x Ykg-1 v Log Swimming Log mg Log mgDate Salinity Length Weight Velocit~ (ppt) (cm) (g) (L sec-) (cms-1/ fl) o2 hr-1 o2 kg-1 hr-1 35.0 29.2 2.290 2. 363 12.769 1.769 2.479 1 35.0 29.2 2.290 2.740 14.805 1.921 1.631 1 35.0 30.5 2.301 2.262 12.494 1.778 2.477 1 35.0 30.5 2.301 2.623 14.486 1.962 2.661 1 1 35.0 30.S 2.301 2.623 14.486 2.038 2.737 1 35.0 30.S 2.301 2. 262 12.494 1.883 2.582 1 35.0 30.5 2.301 2.623 14.486 1.921 2.620 1 2 35.0 24.9 2.146 o.ooo o. ooo 1.377 2.230 2 35.0 24.9 2.146 2.771 13.828 1.766 2.620 , 1 35.0 24.9 2.146 3.213 16.032 1. 769 2.623 1 1 35.0 24.9 2.146 3.213 16.032 1.840 2.694 1 1 35.0 24.9 2.146 3.213 16.032 1.813 2.667 1 2 35.0 31.0 2.447 0.000 0.000 1.723 2. 276 2 Ul J::" (Table 14. cont.) 1 35.0 31.0 2.447 2.581 14.368 2.111 2.664 1 1 1 35.0 31.0 2.447 2.581 14.368 2.125 2.678 2 35.0 30.8 2.441 0.000 o.ooo 1. 714 2.273 2 30.0 29.3 2.415 1.945 10.530 2.076 2.661 30.0 29.3 2.415 2.355 12.747 2.109 2.694 30.0 29.3 2.415 2.355 12.747 2.137 2.722 2 30.0 29.3 2.415 0.000 0.000 1. 700 2.285 2 2 30.0 29.0 2.384 0.000 0.000 1.694 2.310 2 30.0 26 .o 2.292 2.594 13.379 1.898 2.606 1 1 30.0 26.6 2.292 3.008 15. 511 1.994 2. 701 . 1 30.0 26 .9 2.307 2.974 15.425 1.954 2.647 1 2 30.0 32.2 2.465 0.000 o.ooo 1.779 2.313 2 30.0 32.2 . 2.465 2.484 14.098 2.109 2.644 1 30.0 32.2 2.465 2.857 16.213 2.109 2.644 1 1 30.0 32.2 2.465 2.857 16.213 2.163 2.698 1 1 30.0 26.8 2.258 3.843 19.896 1.911 2.653 1 \J1 \J1 (Table 14. cont.) 2 30.0 26 .8 2.258 o.ooo 0.000 1.606 2.349 2 1 30.0 26.7 2.243 3.446 17.805 1.882 2.639 1 2 30.0 26. 7 2.243 o.ooo 0.000 1.602 2.359 2 t H ~:l -----------------------------------------------------------------------------------------------------·>1 'i 25.0 28.5 2.255 0.000 o.ooo 1.526 2.270 1 I·II 25.0 24.2 2.146 3.802 18.702 1.973 2.827 1 ~l I : 1 . 25.0 28.2 2.246 3.759 19.961 2.078 2.832 1 25.0 31.1 2.446 3.183 17.752 2.212 2. 767 ' 25.0 31.1 2.446 3.183 17.752 2.201 2.755 JI 25.0 24.4 2.107 2.828 13. 969 1.862 2.755 ~ 2 25.0 29.1 2. 380 0.000 0.000 1. 593 2.213 2 1 25.0 29.1 2.380 3.471 18.723 2.176 2.796 1 2 25.0 28.7 ' 2. 350 0.000 0.000 1. 704 2.354 2 25.0 26. 5 2.290 3.472 17.872 2.025 2.734 Ul °' (Table 14. cont.) 1 20.0 37.8 2.708 3.042 18.705 2.484 2.776 1 1 20.0 37.8 2.708 3.042 18.705 2.481 2. 773 1 . 20.0 37.8 2.708 2.619 16.102 2.456 2.748 20.0 37.8 2.703 2.434 14.964 ·2. 470 2.766 20.0 37.8 2.703 2.434 14.964 2.435 2.732 20.0 43.5 2.886 1.586 10.462 2.330 2.444 20.0 43.5 2.886 2.115 13.949 2.435 2.548 20.0 43.5 2.886 2.664 17 .436 2.502 2.615 2 20.0 37.8 2.699 0.000 0.000 1.886 2.187 2 20.0 27.0 2. 267 2.556 13.279 1.882 2.615 20.0 27.0 2.267 2. 963 15.396 2.037 2.770 1 20.0 27.0 2. 267 3.741 19.437 2.104 2.837 1 2 20.0 28.7 2.344 0.000 o.ooo 1.598 2.254 2 1 20.0 28.7 2.344 3.519 18.853 2.178 2.834 1 20.0 28.7 2.344 2.404 12.880 1.904 2.560 20.0 28.7 • 2. 344 1.986 10.640 1.758 2.414 20.0 28.7 2.344 2.787 14.933 2.037 2.692 2 20.0 26 .o 2.243 0.000 0.000 1. 563 2.320 2 Ul -::i 1 20.0 26 .o 2.243 3.885 19.808 2.065 2.822 1 (Table 14. cont.) 20.0 37.8 2.673 2.434 14.964 2.285 2.612 1 20.0 25.8 2.201 3.992 20.278 2.037 2.835 1 l; 1 20.0 25.8 2.201 3.992 20.278 2.072 2.870 1 I 20.0 23.3 2.013 1.974 9.530 1. 560 2.547 1t·1 ,j 20.0 23.3 2.013 2.961 14.295 1.736 2.723 :~. 20.0 23.3 2.013 3.433 16. 573 1.806 2.794 " 1 20.0 23.3 2.013 3.984 19.059 1.912 2.899 1 15.0 27.8 2.212 2.482 13.087 1.835 2.623 15.0 27.8 2.212 2.878 15.173 1.940 2.278 1 15.0 27.8 2.212 3.309 17.449 1.987 2.775 1 2 15.0 27.8 2.212 0.000 0.000 1.514 2.302 2 2 15.0 26.4 2.201 o.ooo 0.000 1.646 2.445 2 15.0 26 .4 2.201 2.614 13.429 2.011 2.810 15.0 26 .4 2.201 3.674 18.879 2.049 2.848 15.0 34.8 2.543 2.299 13. 561 2.089 2.546 15.0 34.8 2.543 2.644 15.595 2.225 2.682 \.n 1 15.0 34.8 . 2.543 3.046 17.969 2.350 2.807 1 co 15.0 26 .o 2.188 2.654 13.532 1.947 2.759 (Table 14 cont.) 15.0 26.0 2.188 3. 077 ' 1 15.0 26.0 2.188 3.538 2 15.0 26.4 2.248 0.000 15.0 26.4 2.248 3.030 15.0 30.6 2. 407 . 1.863 15.0 30.6 2. 407 ' 2.614 2 15.0 35.0 2.519 0.000 1 15.0 35.0 2.519 . . 3. 029 1 15.0 27~4 2.220 3.613 15.0 27 ·• 4 2.220 1. 67 9 15.0 41.1 2.866 2.238 Supplemental data, September-October 1976: 10.0 28.2 2.310 2.447' 1 10.0 28.2 2.310 2.943 10.0 26.9 2.223 2.119 10.0 26.9 2.223 2.565 1 10.0 26.9 2.223 2.974 2 10.0 26.9 . 2.223 0.000 15.689 18.043 0.000 15. 57 0 10.304 14.462 0.000 11 ·.917 · 18.913 8.788 · 14.350 12.993 15 •. 630 10.990 13.304 15.425 0. 000 . 1. 977' 2.049 1. 57 2 1.979 2.001 2.073 1.845 2.281 1.991 1.718 2.516 1.870 1.982 1.761 1.840 1.893 1.517 2.789 2.862 1 2 2.324 2.732 2.594 2.666 2. 327 ' 1 2. 763 2.771 1 2.498 2.650. 2.560 2 2.673 2.538 2. 617. 2.670 1 2 U1 2.295 '° (Table 15 cont.) 2 2 10.0 31.4 2.444 0.000 0.000 1.846 2.402 10.0 31.4 2.444 l.·815 10.172 1.982 2.538 10.0 31.4 2.444 1.815 10.172 1. 927' 2.483 1 1 10.0 27 ·• 4 2.265 2.920 l~.283 2.024 2.759 10.0 27 '. 4 2.265 1.350 7 ·• 068 1.709 2.445 2 10.0 27~4 2.265 0.000 0.000 1.584 2.320 2 1 1 10.0 31. 5 2.447' 2.921 16.392 2.186 2.739 2 2 10.0 31.5 2.447 ' 0.000 o.ooo 1.730 2.283 1 10.0 26.0 2 .167. 3.346 17 '.062 1. 907 I 2.739 1 10.0 28.7 ' 2.326 1.968 10.640 1.885 2.559 1 10.0 28.7 " 2.326 2.892 15.493 2.043 2.717 ' 1 2 2 10.0 28.7 ' 2.326 0.000 0.000 1.622 2.296 2 2 10.0 23.l 2.053 0.000 0.000 1.417 ' 2.364 10.0 23.1 2.053 1.991 9.571 1.584 2.531 10.0 23.1 2.053 2. 987 . 14.356 1.618 2.565 1 10.0 23.1 2.053 3.290 15.813 1.789 2.735 1 2 10.0 23.1 2.053 0.000 0.000 1.401 2.348 2 U1 \0 ' OJ (Table 14 cont.) 1 40.0 27 ·• 0 2.230 2.889 15.011 1.878 2.648 1 40.0 27 ·• 0 2.230 2.556 13.279 1.811 2.581 2 40.0 40.0 27 ·•0 27 ·• 0 2.230 2.230 2.111 0.000 10.970 0.000 1.800 1.590 2. 570 2.239 2 1 40.0 40.0 29.4 29.4 2.290 2.290 2.347 ' 2. 517 : 12.726 13.648 ' 1. 93 6 1.950 2.646 2.660 1 40.0 40.0 25.0 25.0 2.152 ......_ 2.152 1.840 2.280 9.200 11.400 1.714 1.7 53 2.562 2.601 1 2 40.0 40.0 40.0 25.0 25.0 29.1 2.152 2.152 2.270 2.560 2. 760 0.000 12.800 13.·000 0.000 l •·811 1.863 1.620 2.659 2.710 1 2.350 2 40.0 29.1 2. 270 1.959 10.566 1.846 2. 577 \ 1 2 40.0 40.0 40.0 29.1 29.1 29.l 2. 270 2.270 2.270 2.371 2.543 0.000 12.791 13.718 0.000 1.925 1.936 1.645 2.656 2.667 · 1 2.375 2 40.0 25.0 2 .107 . 1.840 9.200 1.635 2.528 1 40.0 40.0 25.0 25.0 2 .107 I 2'.107 . 2. 280 2.760 11.400 13.800 1. 753 1.786 2.646 2.679 1 U1 \0 O'" (Table 14 cont.) 2 40.0 26.4 2.201 · 0.000 0.000 1.571 2.364 1 40.0 26.4 2. 207' 2.803 14.402 1.871 2.664 1 40.0 26.4 2. 207 ' 1.288 6.616 1.642 2.435 45.0 40.4 2. 7 57 ' 1.139 1·.237 · 2.204 2.447 ' 45.0 40.4 2. 757 ' 1.708 10.856 2.256 2.499 1 45.0 40.4 2. 7 57 . 1.931 12. 27 2 2.336 2.579 1 45.0 26.3 2.193 1.749 8. 970 1.706 2.513 1 45.0 26.3 2.193 2.167' 11.115 1.753 2.560 1 2 2 45.0 26.3 2.193 0.000 0.000 1.563 2.370 45.0 29.0 2'.272 1.586 8.542 1.799 2. 527 . 1 45.0 29.0 2. 27 2 2.069 11.142 1.834 2.562 1 2 2 45.0 25.4 2.155 0.000 0.000 1.548 2.393 45.0 25.4 2.155 1.811 9.127 1.644 2.489 45.0 25.4 2.155 2.008 10.119 1.644 2.489 45.0 25.4 2.155 2.165 10.913 1.702 2.547' 1 45.0 25.4 2.155 2.244 11.310 1.741 2.586 1 U1 \0 45.0 29.3 2:290 1.570 . 8.498 1.745 2.455 (Table 14 cont.) 1 45.0 45.0 29.3 29.3 2.290 2.290 1.877' 2.048 10,161 11.085 1.799 1.896 2.509 2.606 1 1 2 Data Data at maximum sustained swinuning at resting conditions. rates. U1 \0 p, ' Table 15. Multiple regression equations for oxygen consumption rates at 5ppt salinity ranges. Cynoscion nebulosus data from Blazka chamber 28oc experiments including maximum sustained swimming velocities. July-August 1976. Salinity Range Expected Log Wt. Salinity Velocity Multiple(ppt) N Log mg Constant Xw Xs Xv Correlation Equation 02hr-l (g) (ppt) (L sec-1) - ,.30-35 32 y = -1.1379 +l.2364Xw -0.0033Xs +0.1236Xv 0.95 41 25-30 26 ,.. y = -0.8196 +l.1123Xw -0.0044Xs +0.1269Xv 0.96 42 ,.. 20-25 36 y = ·-0.8035 +l.0122Xw +0.0015Xs +0.1555Xv 0.98 43 ,. 15-20 48 y = 0.5705 +0.9952Xw .;..o.0073Xs +0.1491Xv 0.98 44 Supplemental data, September-October 1976: ,.. 10-15 45 y = -0.7810 +0.9910Xw +0.0108Xs +0.1271Xv 0.98 45 35-40 37' A y = -1.559 +l.1699Xw +0.0126Xs +0.1285Xv 0.96 46 40-45 37· y = -0.3898 +l.OlllXw -0.0067Xs +0.1067Xv 0.98 47 · ,. 25&35 26 y = -• 9233 +1.1407Xw -0.0045Xs +0.1445Xv 0. 97 . 48 °' 0 ~ 2 • Y kg-1 hr-1 = 1.9943 + 0.1216Xs -0.6096Xl0-2xs+ 0.1230Xlo-3xs3 -o. 9123x10-6xs4· The use of sufficient significant digits is mandatory for the higher order coefficients which adequately cover the sinuous metabolism-salinity curve between 10 to 45 ppt but not beyond. The technique of making these calculations is in Snedecor and Cochran (1967) and other statistical books; it is simply an adaptation of the multiple regression technique by using X, x2, x3, and x4 as the multiple, independent variables with Y/kg-1 hr-1 as the dependent variable. • Since the metabolism and swimming velocity was apparently depressed at 30 ppt because those fish were in poor physical condition, the 30 ppt data w~re omitted altogether for the above fourth-order equation. ' • • DISCUSSION Nueces Bay Autumn Data From the data and calculations in Table 1 and 4, the log weight-log length analysis of covariance computations in Tables 2 and 3, and the metabolism comparisons in Fig. 1, it is apparent that carnivorous Cynoscion nebulosus undergo a late summer and autumn period of metabolism and growth depression with general debilitation. Since the same situation prevails for the Mugil cephalus, the striped mullet, in later summer months, the need to assemble data to establish whether the growth-metabolism de­ pression is a gener~lity becomes essential (Cech and Wohlschlag, 1975). Quite clearly fish morbidity is inevitable when standard metabolic levels are depressed. From the 35 and 45 ppt metabolic • levels and the trend between these levels in Fig. 1, it is easy to see that metabolic scope above the normal standard line of summer fish is much reduced. From data reviewed in Fry (1971), it would appear that routine scope would -have to be about twice the standard level to allow for minimum foragipg energy and/or the energy required for digestion and assimilation (specific dynamic action). Thus, if the "normal" standard level at 35 ppt for the summer fish is reasonable at about 2.28 log units (191 mg 02 kg-l hr-1), then the comparable autumn routine value of 2.39 log units (245 mg o2 kg-l hr-1 ) is far short of double the standard rate. In terms of salinity and the position of the standard and routine lines in Fig. 1, it would seem that the "least unfavorable" salinity at this season would certainly be • less than 35 ppt. • Since published data on possible food deficiencies and data on the possible cumulative, physiologically adverse effects of sustained high summer temperatures are also unavailable for this area and elsewhere, it seems reasonable to propose that there be conducted much more research on these two possibilities if other environmental stresses are to be evaluated. These deficiencies could be -evaluated either by (1) physic-logically oriented studies of freshwater inflows on coastal areas with -the use of "standardized" fishes kept on rigid laboratory temperature and feeding regimes or (2) more extensive ecological studies for the evaluation of energetics of fish feeding and food requirement levels especially in late summer. While laboratory studies could efficiently be used for assessing the effects of • salinity and temperature stresses, ecological studies would still be required for assessing the availability of food organisms and for determining the efficiency of food utilization, especially under naturally stressed conditions. In the natural environment there also is.the likelihood that larger members of fish populations react more adversely to stress than smaller members. Along the south Texas coast this appears to be true for the pinf.ish, Lagodon rhomboides as indi­cated by Wohlschlag and Cameron (1967), Wohlschlag et al. (1968) and Kloth and Wohlschlag (1972). In the case of the autumn data on spotted seatrout (Table 2) the log weight-log length coeffi­cient of 1.8 is so low that the larger fish must certainly have experienced relatively much greater weight losses than the smaller • fish. Autumn -Winter Seawater Series • This series, designed to yield performance baseline data at colder temperatures, indicates quite cJ..early that there is little shift in optimal salinities for winter fish (Fig. 2). There is no ready explana­ tion for the differences in Fig. 2 for the 15° and 2s0 c standard-routine metabolism data pairs in terms of the shape of the curves. If either the 15° standard or routine levels are extrapolated upward at 20 ppt to 25° with a bt ~ 0.02 (Eq. 21, Table 7a), both levels are somewhat lov.rer than the observed 2s0 c standard and routine levels. Thus the extrapolation of winter 15°C to autumn 25°C metabolic levels indicates • the reverse of cold adaptation in the sense observed for polar fish (Wohlschlag 1964). Bolton's (1974) question on the validity of the cold adaptation concept would be affirmed if the 15°C levels extra­ polated to 25° were about equal. Because the upwardly extrapolated levels are lower than expected at approximately corresponding levels of activity, either the btu:> 0.02 is much too low or there is a possi­ bility of cold depensation. Either possibility is realistic on the basis of the available data. By contrast the summer (Fig. 1) routine levels at 2s0 c are based on rrn.ich higher swimming rates (Xv) than the rates observed for the autumn and winter experiments. Allowing for the temperature and acti­ vity differences, the 28° and 25°C data for summer and au"tumn are rea­ sonably similar. However, the comparative levels of the routine scope are much • higher in the summer at 2s0 c (see Fig. 3) and near the optirrn.im salinity • level of about 20 ppt than the routine scope levels at autumn and winter (Fig. 2) because of the much higher routine swimming rates in summer. In Table 16 are the results of an attempt to utilize the various pertinent equations of Table 7 to "adjust" all of the routine rates at the various salinity and two temperature levels to a uniform bv = 1.0. As can be observed the newly calculated routine scope values at bv = 1.0 are rather erratic compared to the values calculated from the observed data. The erratic values are clearly in large part the result of erratic bv computations from very low swimming rates by sluggish fish. Because the fish were ordinarily allowed to swim in the chamber at whatever speeds they would swim consistently, the results in the fall and winter • are for very slowly swimming fish with a spread of Xv so small that bv values from the multiple regression calculation have very poor precision. Whatever the advantages may be for using routine swimming rates from ''naturally" swimming fish, a range of observed Xv swimming rates from zero to at least 1.5 L sec-l would seem desirable for regression calculations of bv. San Antonio Bay February-March Data Because the San Antonio Bay experiments emphasized both low temperature and low salinity aspects of routine and standard metabolism, these data are best compared with the winter seawater series at 15°C and the lower salinity levels. Calculations for the evaluation of scope for routine activity are in Table 17. At 10.9 and 20.0 ppt and at 15°C the SAB scope values are both 0.329, • which indicates no diminution in scope with declining salinity as Table 16. Scope for routine metabolism at observed average swimming activity and at calculated values of 1 Lsec-1 over selected salinity and temperature ranges. Seawater (SW), winter. Cynoscion nebulosus data. Routine Activityl Standard Average Observed Xv = 1.0 Metabolism Scope Equations ;alinity Activity Log Log Log Observed Xv = 1.0 for ~ = 1.0 . ppt Lsec-1 mg02 kg-1 hr-1 rng02 kg-1 hr-1 mg02 kg-1 hr-1 mg02 kg-1 hr-1 mg02 kg-1 hr-1 Calculations ~t 25oc, November -December: 14.0 0.545 2.256 2.315 2. 070 62.1 89.0 (11) 18.4 0.830 2. 407 ' 2.430 2.125 · 121.9 135.8 (11) ' (12) 22.9 0.843 2.446 2.238 2 .187' 125.5 19.2 (12) ' (13) 25.0 0.635 2.400 2.432 2.272 64.1 83.3 (13) \t 15°c, January -February: 14.2 0.464 2 .177 . 2.235 2.049 38.4 59.9 (15) 17. 2 0.737 2.140 2.172 1.804 74.3 84.9 {15) ' (16) 22. 7 . 1.092 2.262 2.255 1.995 83.9 81.0 (16) ' (17) 23.9 2 1.158 2 2.329 2... 2. 7 57 . 2.202 2 54.1 2 412.3 2 (17) 24. 7 . 0. 757 ' 2 .167 . 2.211 2.025 41.0 56.7 · (17) · When 2 equations are used, average Xv = 1 responses are calculated. Based on only 4 observations on small fish. °' °' Table 17~ Scope for routine metabolism at observed average routine swimming activity and at selected salinities and temperatures. Cynoscion nebulosus in San Antonio Bay waters. February-March, 1976. Observed Routine Standard Average Metabolism Metabolism Salinity Temp. Activity Log Log Scope ppt Oc Lsec-1 mgo2 kg-1 hr-1 mg02 kg-1 hr-1 mg02 kg-1 hr-1 Equations 10.9 15.0 0.815 2.200 1. 871 84.2 22, 24 10.9 10.0 0.615 1.938 1.630 44.0 23,24 20.0 10.0 0.378 1.946 1.751 31.9 23,25 20.0 15.0 0.419 2.144 1.815 74.0 25 .....J °' • in case of the seawater plots of Fig. 2, but the scope values at 15°C are about the same at 20 ppt for both winter SW and SAB experiments, but SAB scope is much higher at l0.9°c when compared to an extrapolated value in Fig. 2 SW series. However, in both winter SW and SAB data sets, the standard · and routine activity levels tend to be of the same general magnitude if allowance is made for the lower temperature level in the SAB data and slight differences between the SAB and SW swimming velocities. The similarity of standard and routine metabolic levels of SAB and comparable SW data implies that there are no unusual stress factors in the SAB waters that would elevate or depress metabolism. The lack of SAB stress effects also implies that the 10.9 ppt data at both looc and 15°c would be especially useful when combined • with multidimensional analyses of scope and other measures of swim­ming propensities in terms of both salinity and temperature vari­ables. Lavaca Bay Waters -April The standard and routine metabolic levels for salinities of 19-20 up to 30 ppt and from 15°C to 24-25°c are of the same general levels as those for the seawater and San Antonio Bay waters, if comparable temperatures and salinities are considered. At the very low swimming speeds the calculation of meaningful oxygen consumption rate-swimming rate coefficients bv is difficult as indicated by the data in Table 10 and by the derived regressions in Table 11 in which most of the bv are negative. (See Results • section above.) As explained earlier, the energy expended at very low, less efficient swimming rates is quite possibly greater than at higher • swimming rates when well coordinated, highly efficient caudal propulsion is the principal mode of swimming. Webb (1975) sum­ marizes much of the existing information on the relations between swimming speeds and kinematics; he notes that ma.ny of the rela­ tionships apply to swimming speeds that are higher than 1-2 L 1 sec-. In the Lavaca Bay water experiments, for example, the 1 spotted seatrout swimming speeds averaged less than 0.5 L sec- and it was obvious that the swimming mode(s) at these low speeds appeared to result in "labored" or "clumsy" swimming movements compared to the more effective, typical subcarangiform movements at higher speeds. The trans!tion in _swimming modes would be at about 0.3 -0.4 L sec -1 for the spotted seatrout and may be as­ sociated with the solitary swimming vs. natural schooling energy • requirements for propulsion as was observed for an antarctic fish (Wohlschlag, 1965) and for the bluegill (Wohlschlag and Juliano, 1959). Otherwise, the presence of increased "spontaneous activity" (Fry 1957) at the very low Xv could also be an acceptable expla­nation for the negative bv values. In spite of these small, negative and statistically uninteresting bv, the overall equations " " -1 yield reasonable estimates of Y or Y kg which agree not only with the average Ykg-1 hr-1 from Table 10, but with the averages at comparable temperatures and salinities in the seawater and San Antonio.·Bay series, as well as with the Nueces Bay series in the following section. The Lavaca Bay scope data are in Table 18~ where the values indicate reasonable correspondence with scope values for • the San Antonio Bay and winter sea water series . Table 18. Scope for routine metabolism at observed average routine swimming activity and at selected salinities and temperatures. Cyn·oscion nebulosus in Lavaca Bay waters. April, Average Salinity Temp. Activity ppt oc Lsec-1 19.0 15.0 0.499 19.0 15.0 0.462 20.0 25.0 0.450 30.0 24.0 0.358 30.0 15.0 0. 37 5 1 From regression based on 2 From regression based on 3 From regression based on 1976 Observed Routine Metabolism Log mg02 kg-1 hr-1 2.065 1 2 2.154 2.357 •3 2.298 2.092 Standard Metabolism Logmg02 kg-1 hr-1 1.840 1.840 2.123 2.094 1.856 original LBlA-J data and assuming bv LBlB-J data and assuming bv = 0.15. LB2A-J data and assuming bv = 0.15. 4 From average based on regression from LB4A-J data and from Eq. Scope mgo2 kg-1 hr-1 46.9 73.4 94.8 74.4 51.8 = 0.15. LBlA deleted. (30) • Equations Extrapolated 1 Extrapolated 2 Extrapolated 3 30 4 30 ....J • Nueces Bay Waters -May-July The original aim of obtaining· the T~ble 12 data and Table 13 equations was for a low temperature comparison of the 1975 summer pilot project and early autumn 1976 series at 28°c. Al­though this portion of the project was too late in the season for natural "cold water" experiments, the cooling of the waters and the sufficiently long acclimation t ·imes at the lower temperatures produced reasonable metabolic rate results, with possibly the exception of the July data at 15° (Table 12). At these low tern­ peratures the July fish may not have been too well acclimated, inasmuch as they appeared "sluggish", while two fish in this series were obviously comatose with insignificant metabolism. Even so the summary of the average routine and standard metabolic • rates and the scope in Table 19 indicate no unusual levels con­sidering the low temperatures and the salinity extremes of 10 and 32 ppt. At 24-25°c the standard levels were lower than for the August 1975 pilot project data, whose elevated standard and routine metabolic rates apparently indicated a sublethal level of stress in the Nueces Bay waters at that time. The 1976 Nueces Bay waters apparently did not influence the standard and routine metabolic levels over and above (or below) those of the seawater experiments at comparable salinities and temperatures. However, the Xv for these data are lower than those at 15 and 25 ppt in the original pilot project data for Nueces Bay, but are about equivalent to those of the depressed • autumn 1975 35 and 45 ppt data . Without major "adjustments" of these Nueces Bay data for swimming velocity differences, the scope values are of the same Table 19. Scope for routine metabolism at observed average routine swimming activity and at selected salinities and temperatures. Cynoscion ne·bulosus in Nueces Bay waters. May-July 1976. Observed Routine Standard Average Metabolism Metabolism Salinity Temp. Activity Log Log Scope ppt oc Lsec-1 mg02 kg-1 hr-1 mgo2 kg-1 hr-1 mgo2 kg-l hr-1 Equations 32.0 15.0 0.468 1.963 1.618 50.3 32' 35 32.0 24.0 0.601 2.301 2.045 89.1 32, 36, 38 20.0 15.0 0.472 2.034 1.696 58.4 33a,38a,39a 20.0 25.0 0.625 2.330 1.974 ' 119. 6 33a,36a,38a,39a 10.0 25.0 0.782 2.369 1.952 144.4 37a,39a 10.0 15.0 0.514 1.959 1.623 49.0 34, 39a " N • order as the autumn seawater series and the series for San Antonio and Lavaca B~ys. By contrast: (1) the pilot project NB series had higher standard and routine rates presumably due to sublethal water quality stresses, and (2) the autumn NB series had depressed standard and routine rates presumably due directly to the poor conditions of the "starved" fish. Ma~imum Sc~pe fo~ Activity The series of metabolic data at maximum sustained swimming rates, determined with the Blazka apparatus, can give a much more sensitive scope calculation than the routine scope calculations. The rationale for scope as a sensitivity measure of the response by an organism to environmental regimes--or variations among a given set of environmental conditions--has been well documented • (Fry 1947, 1957, 1971, and others) with reference to maximum optimal metabolic output at optimal temperatures. Although there has been limited research on metabolism as related to salinity, the studies of metabolic scope over salinity regimes have been even more limited. In the pilot project for routine scope calculations, the results indicated clearly that a salinity of about 20 ppt provided maximum scope. Whether there would be the same relationship to salinity at a scope value from metabolic data at maximum sustained rates was a primary objective for this portion of the study. Secondary objectives included a comparative assessment of the nature of (a) maximum sustained swimming rates themselves at different salinities, (b) the charac~ teristics of the curves relating maximum, routine and standard • metabolism· to salinity, and (c) the characteristics of the scope curve. • The data from Table 14 and the calculated regressions from Table 15 provide the summarized informati_on on swimming speeds and metabolism for estimates of scope at 1()-.45 ppt. (Note that -1 ' r-:;:--1 r-:;:-­ the term L sec Iv L is the same as velocity in cm sec-v L when Lis fish lengths in cm.). The summary is in Table 20, • The relationships of the metabolism-salinity plots for standard, routine, and maximum sustained metabolism and scope are, for the most part, self explanatory in Figure 3. One obvious fact persists: the optimum salinity at the scope for maximum sustained swimming speed is at about 20 ppt, the same as the salinity level for the scope for routine swimming activity in the preceding sections cover.ing both summer and winter tern­perature ranges . It is interesting, and quite useful, to observe that the metabolic rate of the single most active fish at any given sali­ nity as indicated by squares in Fig. 3 suggests a curve that parallels the average maximum metabolic rate vs. salinity points (encircled points). Another important feature of Figure 3 is that the scope for routine activity at about 10 and 45 ppt implies about twice the standard oxygen consumption rate at routine activity rates. This salinity range in the south Texas coastal region is just about that over which the spotted seatrout regularly occur at least in fair availability to the sport and commercial fisheries. Fry's (1957) suggestion (from Job's data on small brook • trout) that at least twice the standard oxygen consumption rate was required for assimilation would certainly seem rational for . ·•·· Table 20. Observed and average maximum values for swinuning velocities (lengths per second) and velocities per square root of length, log 02 consumption per kg per hr, and standard swimming activity. metabolism and scope for maximum sustained Scopel Max. Max. Log Avg. Max. Standard! for Max. Observed Avg. Max. Observed Avg. Activity Salinity Max. Xv Xv Max. Xv VL XvyL mg 02 Log mg 02 Log mg 02 kg-1 hr-I mgo2 kg-1 hr-1 (ppt) (L sec-1) (L sec-1) kg-1 hr-1 35 3.213 2.823 16. 03 2 15.011 2.694 2.664 2.2731 306.8 30 3.843 2 19.896 2 3.164 16.844 2.701 2.6643 2.1691 313. 7 . 30 3.446 i1 ·.805 2.0121 53 9. 7 ' 25 3.802 3. 677' 18.702 19.129 2. 827 . 2.818 2. 870 . 2. 831 2.0771 558.2 20 3.992 3.646 20.278 ·19.390 2.1951 468.5 15 3. 674 3 e 3 07 I 18.913 18.058 2.862 2.796 Supplemental data, September-October , 1976: 10 3.346 3.041 17 ·.062 15.871 2.759 2.719 2.3304 311.3 2.710 2. 671 2.3624 23 8. 7. 40 2.889 2.712 15.011 14.063 45 2.244 2.092 12. 27 2 11.385 2.606 2. 579 2.3824 138.3 1 Based on 1975 "Pilot Project" standard metabolism determinations at 15,25,34,35,45 ppt or extrapolated between. .....J 2 Small fish "sheltered" in chamber; values possibly erroneously high. U1 3 Fish in poor condition~ 4 Lowest in Blazka Avg. Y kg-1 at Xv = 0. • Figure 3. Upper panel -Metabolism of Cynoscion nebulosus • at standard (lower iine, diamonds), routine (middle line, triangles) and at maximum sustained activity (upper lines, circles) over a range of salinities. Calculated rates indicated by squares for the various numbered equations from Table 15. Lower panel --Scope for maximum sustained activity over salinity range 10 -45 ppt. Arrows indicate "depressed" values . • • 600 48 42 El ~41 0 1f - I a: J: • - I 0 a: J: ;1( - I (!) ~ 200 N 0 I •(!) 0 30 40 50 SALIN IT/~ 0/oo • the spotted seatrout. This suggestion is borne out by the fact that the seatrout in the cooling ponds of the Flour Bluff, Texas power plant had a very abundant late summer-early autumn food supply. These fish were much fatter and in far better condition than other fish in the coastal areas at around 28°c and 25-32 . ppt, where hypothetically considerable swimming energy would be required just to secure food in addition to assimilating it. While this hypothesis would explain the depressed metabolism and poor condition of the 1975 autumn fish compared to the summer fish used in the Blazka chamber experiments, it is beyond the purview of this study to develop the subject of energetics of feeding, assimilation and growth. It should be emphasized how­ever that fish utilized for initial studies of salinity, temper­ • ature and other stress effects should be healthy, growing fish functioning under aerobic metabolic conditions. It would be doubtful that the rather emaciated autumn fish for the Nueces Bay water study at 35 and 45 ppt and 28°c with depressed standard and routine metabolism could have a very high sustained swimming performance rate unless they had propensities for large scale anerobic metabolic processes. One of the more evident features of the metabolic levels at maximum sustained swimming rates is that the swimming rates also have their maximum values at the optimal salinity around 20 ppt in the same manner as both the metabolic level and scope. In Fig. 4, top panel, the maximum sustained swimming rate is • plotted against salinity (upper line) to emphasize this obser­vation. The similar plot for the routine swimming rate (lower • Figure 4. Swimming characteristics of Cynoscion nebulosus at different salinities. Top panel: Swimming speeds -1 in body lengths (cm) sec ; circles, maximum sustained speeds; triangles, routine speeds. Bottom panel: Swimming speeds in cm sec-l (U) divided by square root of length in cm; circles, average maximum values; • -0.5 squares, individual maxima. Note the U·L value for one small fish that "sheltered" itself at bottom front of chamber to "block" or reduce effective flow rate far below measured flow rate . • . 4 3 2 - I 0 LL.I -&------~,~­ (/) ...J oL-----r----.-----.---.----.----.~--y---.-~ • 21 SMALL FISH 20 f":'l II L!J -"SHELTERED 19 18 M? I ....J ::> 17 16 • 10 20 30 S A LI N I TY -0/oo • line) does not show the same relationship, although in some but not all of the previous experiments the routine rates also are at a maximum at about 20 ppt salinity. In Fig. 4, lower panel, the swimming rate as U cm sec-l divided by the square root of fish length in cm shows the same optimum at about 20 ppt both for the averages of the maximum s~imming rates (lower line) and for the maximum rates of indivi­ dual fish at each salinity interval. The single fish at 30 ppt with the ·'rapparent" very high U·L-O • 5 that had "sheltered" itself by partially blocking the water flow obviously had much lower • a "virtual" swimming rate. One of tne great advantages of the Blazka apparatus is that at higher velocities such aberrant be­havior is much easier to detect than are corresponding aberrancies at lower velocities in the circular chamber. Also routine rates themselves at constant, but ad libitum, swimming speeds, more are difficult to define. The behavioral tendencies of the spotted seatrout are admirably suited for the easy recognition and measurement of maximum sustained swimming rates. When the maximum attainable rate is but slightly exceeded, first the fish tend to drift to the back screen gradually and then "burst" slightly to the middle or anterior portion of the tube; then the process tends to be repeated with increasing frequency. Quite likely anaerobic re­ spiration begins at this point. Interpretations of Data Analysis While the evaluations above establish adequately the optimal • salinity at about 20 ppt on several bases, some further evaluations are pertinent to the development of improved analytical techniques. 82 • Once a given species is selected for use in assessing freshwater influx requirements, three major experimental rationales and protocols are suggested. The first invol~es measurements in the field for a strictly ecological approach. This approach in­volves technological problems of (a) using respiration chambers in the field, (b) carrying on experiments over extended time and space to gain information over a desired range of temperatures, salinities, etc. and (c) having personnel who can operate and maintain experimental regimes under field conditions; problems of obtaining field-derived standard metabolism data are not easily resolved; and problems of controlling or assessing extraneous natural variability among fish may be difficult, although some of the author's earlier work in polar areas reveals that "uncontrolled" variability• is not excessive. The second series of rationales and protocols are those involved in the present field-laboratory study with all the advantages of laboratory controlled conditions, but with considerable disadvantages and costs of obtaining and transporting both water and fish on demand. The third set of considerations involves a strictly physiological, laboratory approach that has both advantages and disadvantages. Advantages are (a) the pos­sibility of having ready access. to a stock of experimental fish maintained on tightly controlled regimes, (b) stock fish can be pre-acclimated (or "acclimatized") to experimental conditions far in advance of actual measurements and (c) there can be better control on some, but not necessarily all, variables under study; disadvantages are that (a) decisions on what to control on labor­• atory stock fish when naturally varying factors (like short term ·93 • temperature variation, feeding, activity, etc.) are often not easily recognized due to lack of knowledge of natural environ­ • mental stress; and (b) there may always be the possibility that laboratory experimental results cannot be directly applied to· field conditions. The need to be apprised of natural variability in the condition of fishes can be iilustrated by investigation of the seemingly depressed values of the active metabolic rates at 30 ppt. in the Blazka experiments. Especially critical is the evaluation of the depressed rates that could be expected when fish are in declining physical condition as indicated earlier for the autumn fish in the Nueces Bay experiments. For the several fish used in the maximum swimming rate experiments, it appeared (after the experiments were conducted) that these fish were in poor condition. Compared to the normal Guest and Gunter (1958) data and the autumn and summer regressions of log weight on log length (Table 2), the individuals in maximum swimming rate experiments show a distinct depression in condition in Fig. 5. These weight-length plots compare with the autumn 1975 Nueces Bay experiments, in which the fish were also progressively more emaciated with increasing length. One of the more important types of critiques for this study involves the use of the linear multiple first order • regressions for the estimation of the oxygen consumption in relation to body weight, swimming velocity, salinity and temperature. The coefficients for the body weight seem rather • Figure 5. Log weight --log length regressions showing relative position of Blazka fish with depressed metabolism at maximum sustained swinuning activity (circles) and at 30 ppt. Guest and Gunter (1958) data used for regression for more or less average fish. Autumn 1975 regression from fish in declining condition used in Nueces Bay water • experiments; summer 1975 regression data from seawater experiments on relative thin, but healthy, fish • • • 3.0 2.8 Guest and Gunter - Ct ._.,., 2.6 ~ :c (!) • LaJ ~ (!) 2.4 2.2 0 _J 0-Experimental Fish 2.0 2.40 2.45 2.50 2.55 LOG LENGTH (mm) • • high (bw>0.8) in many cases an~ weights are negatively coreelated with swimming speed for many of the partial • correlations (not tabulated for the individual regressions) • These problems have been discussed widely (~-~., Moore 1976; Webb 1975; Griffiths and Alderdice 1972; Fry 1957·, 1971; Fry and Cox 1970; Brett 1964, 1965, 1967; and others). Quite obviously a very large actively swimming fish in a small chamber would have its swimming inhibited, but there is also the actuality of correlation between weight (and length) and swimming velocity for hydrodynamic reasons (Webb 1975). For the Blazka chamber experiments in the Fig. 6 comparisons are of interest in comparing observed values from group averages, and values from a fourth order equation (based on the log y kg-1 hr...1 at maximum Xv) in the form: " . 3 4 y kg-1 = a + b1xs + b2Xs2 + b3Xs + b4Xs or " 2 y kg-1 = 1.9943 + 0.12156 Xs -6.0960Xl0-3 Xs + l.2302x10-4xs -9.123ox10-7xs4 where Xs includes the values from 10 to 45 ppt excluding 30 ppt data. Using the variates in the form of Y kg~l for the maximum activity values represents only a part qf the infor­mation available on weights, salinities and swimming rates, and especially information that may be contained in inter­actions among these variables. The values calculated from Sqs. 41-48 (Table 15), on the other hand, involve only adjacent salinity (5 ppt) levels (10 ppt in case of Eq. 48),• with most of the bs salinity coefficients statistically of Q 87' • Figure 6. • Comparisons in "precision" of maximum sustained active metabolic rate calculations in relation to salinity. Encircled points are averages of maximum values from Table 20. Curved line through points calculated by fourth order equation based on all maximum swimming rate data except at 30 ppt. Equation (48) from 25 & 35 ppt from Table 15 is used to calculate value within square at average swimming rate and weight to compare with the depressed observed average value at 30 ppt (arrow) . • r--------------------~----~---------0 L() • 0 q­ ./· .£ 0 r'> / m . 0 0 ;· v >­ 0 I­ • /. ~ z _J t , c~· • • • 97 Brett, J.R., J.E. Shelbourn, and C.T. Shoop, 1969. Growth rate and body composition of fingerling sockeye salmon, Oncorhynchus nerka, in relation to temperature and ration size. J. Fish. Res. Bd. Canada, 26:2363-2394. Cech, J.J., Jr. and D.E. Wohlschlag, 1975. Summer growth depression in the striped mullet, Mugil cephalus L. Contr. Mar. Sci., Univ. Texas, 19:91-100. Cech, J.J., Jr. and D.E. Wohlschlag. Seasonal patterns of respiration, circulation, and hematological charac­ teristics in the stripped mullet, Mugil cephalus L. Ms. submitted. IBP Theme B, Man's Effect on the Marine Environment. Cambridge. Collins, J.H., 1974. Effects of salinity on the respira­tory metabolism of Mugil cephalus. M.A. Thesis, Univ. Texas, xi + 118 pp. Fry, F.E.J., 1947. Effects of the environment on animal activity. Univ. Toronto Studies Biol., Ontario Fish. Res. Lab., 68:1-62. Fry, F.E.J., 1957. The aquatic respiration of fish, pp. 1-63. In: M.E. Brown (ed.), The Physiology of Fishes, Academic Press, New York. Fry, F.E.J., 1971. The effect of environmental factors on the physiology of fish, p. 1-98. In: w.s. Hoar and D.J. Randall (eds.), Fish Physiology, Vol. 6, Envi­ rorunental Relations and Behavior, Academic Press, New York • • Fry, F.E. and E.T. Cox, 1970. A relation of size to swimming speed in rainbow trout. J. Fish. Res. Bd. • Canada, 27:976-978. Griffiths, J.S. and D.F. Alderdice, 1972. Effects of acclimation and acute temperature experience on the swimming speed of juvenile coho salmon. J. Fish. Res. Bd. Canada, 29:251-264. Guest, W.C. and G. Gunter, 1958. The seatrout or weak­fishes (Genus Cynoscion) of the Gulf of Mexico. Gulf States Mar. Fish. Comm., Tech. Summary 1:1-40. Gttnther, B., 1~75. Dimensional analysis and theory 6f biological similarity. Physiol. Rev., 55:659-699. Holeton, G.F., 1974. Metabolic cold adaptation of polar fish: fact or artifact? Physiol. Zool., 47:137-152. Jones, D.J., 1971. Theoretical analysis of factors which may limit the ·maximum oxygen uptake of fish: the oxygen cost of the cardiac and branchial pumps. J. Theor. Biol., 32:341-349. Kloth, T.C. and D.E. Wohlschlag, 1972. Size-related meta­bolic responses of the pinfish, Lagodon rhomboides, to salinity variations and sublethal petrochemical pollution. Contr. Mar. Sci., Univ. Texas, 16:125-137 . . Mar, J., 1959. A proposed tunnel design for a fish respi­rometer. Pac. Nav. Lab., Esquimalt, B.C., Tech. Memo. 59-3:1-13 • • • Moore, R.M., 1976. Seasonal patterns in the respiratory metabolism of the mullets Mugil _cephalus and Mugil • curema. Contr. Mar. Sci., Univ. Texas, 20:133-146. Nordlie, Frank G. and Charles W. Leffler, 1976. Ionic regulation and the energetics of osmoregulation in Mugil cephalus Lin. Comp. Biochem. Physiol. 51A: 125-131. Snedcor, G.W. and W.G. Cochran, 1967. Statistical Methods. Iowa State University Press, Aines, Iowa. Smith, L.S. and T.W. Newcomb, 1970. A modified version of the Blazka respirometer and exercise chaniber for large fish. J. Fish. Res. Bd. Canada, 27:1321-1324. Webb, P.W., 1975. Hydrodynamics and energetics of fish propulsion. Bull. Fish. Res. Bd. Canada, 190:·1-158. Wohlschlag, D.E., 1964. Respiratory metabolism and ecological characteristics of some fishes in McMurdo Sound, Antarctica, p. 33-62. In: M.O. Lee (ed.), Antarctic Research Series, Volume 1, Biology of the Antarctic Seas, Ainerican Geophysical Union, Washington, D.C. Wohlschlag, D.E. and R.O. Juliano, 1959. Seasonal changes in bluegill metabolism. Limnol. Oceanogr., 4:195-209. Wohlschlag, D.E. and J.N. Cameron, 1967. Assessment of a low-level stress on the respiratory metabolism of the pinfish (Lagodon rhomboides). Contr. Mar. Sci., Univ. Texas, 12: 160-171. · • '• ' ;---,. "' ••• ~ '~ ..., • !'<" • -~· , .•• ' ,. ·:'>. ' • Wohlschlag, D.E., J.N. Cameron and J.J. Cech, 1968. Seasonal changes in the respiratory metabolism of the pinfish • (Lagodon rhomboides}. Contr. Mar. Sci., Univ. Texas 13:89-104. Wohlschlag, D.E. and J.J. Cech, 1970. Size of pinfish in relation to thermal stress response. Contr. Mar. Sci., Univ. Texas 15:22-31. Wohlschlag, D.E., W.L. Longley, Jr., R.H. Moore and F.R. Parker, Jr. Respiratory metabolism of the striped mullet, Mugil cephalus, in an evaluation of sublethal stresses in Galveston Bay, Texas. Manuscript submitted. IBP Theme B. Man's Effect on the Marine Environment, Cambridge . Wohlschlag, D.E. and R.H. Moore. Prolonged thermal and salinity effects on the mullet, Mugil cephalus, with reference to seasonal changes in metabolism and growth. Manuscript submitted. IBP Theme B. Man's Effect on the Marine Environment, Cambridge.