• • • • • • • • • • • ANALYSIS OF FRESHWATER ON METABOLIC STRESSES BAY AND ESTUARINE RATES OF ADAPTABILITY SALINITY-TEMPERATURE REGIMES Draft Final Report to: ­Texas Department of Water Resources Interagency Cooperation Contract No. IAC (78-79)-1840 TDWR Contract No. 14-90019 THE LIBRARY OF THE UNIVE._ SlTY OF TEXAS * AT AUSTIN • INFLOW EFFECTS OF SOUTH TEXAS • FISHES: TO CHANGING • • • • • • • • • • THE UNIVERSITY OF TEXAS • MARINE SCIENCE INSTITUTE Port Aransas Marine Laboratory • • January 8, 1980 Port Aransas, Texas 78373 Phont512 749-6711 Texas Department of Water Resources 1700 N. Congress Avenue P. o. Box 13087 Capitol Station Austin, Texas 78711 Attention: Dr. Herbert W. Grubb Mr. Gary L. Powell Gentlemen: The accompanying report is submitted with great pleasure. It is "ANALYSIS OF FRESHWATER INFLOW EFFECTS ON METABOLIC STRESSES OF SOUTH TEXAS BAY AND ESTUARINE FISHES: RATES OF ADAPTABILITY TO SALINITY-TEMPERATURE REGIMES." The support was under IAC (78-79)-1840, TDWR Contract No. 14-90019. We send our sincere thanks for this support. The report is almost entirely based on the M.A. thesis, "STUDIES ON THE TIME COURSE OF ACCLIMATION TO SALINITY CHANGES IN JUVENILE SPOTTED SEATROUT AND RED DRUM," which has been submitted to the University of Texas Graduate School by Mr. Michael P. Gunter. The numbering of the tables and figures in the report follows that of Gunter's thesis. In addition to Mike Gunter, special acknowledgements are due to Ron Ilg, who helped initiate work on the small fish earlier and who is continuing work with them for his Ph.D. dissertation. Throughout these investigations on the south Texas estuarine fishes, the general perspective and advice afforded by .Mr. Gary Powell and other TDWR personnel ha~e been highly valued. The initial TDWR investigations have thus opened up a number of very promising and practical research avenues. Apologies for the lateness of this report are due solely • to the principal investigator's unavoidable 1-1/2 year delay in completing the previous report. The forebearance of TDWR in this matter is greatly appreciated • • • • • • • Texas Department of Water Resources January 8, 1980 Page 2 • Again, we all emphasize our gratitude for the TDWR support during the past several years • Respectfully submitted, Donald E. Wohlschlag Principal Investigator Professor of Zoology and Marine Studies DEW:hg Dist: 25 copies TDWR • • DRAFT FINAL REPORT • • TO TEXAS DEPARTMENT OF WATER RESOURCES • • • • • • • • • • • for Interagency Cooperation Contract No. IAC (78-79)-1840 TDWR Contract No. 14-90019 • ANALYSIS OF FRESHWATER INFLOW EFFECTS ON METABOLIC STRESSES OF SOUTH TEXAS BAY AND ESTUARINE FISHES: • RATES OF ADAPTABILITY TO CHANGING SALINITY-TEMPERATURE REGIMES • Principal Investigator: Donald E. Wohlschlag • Research Assistants: Ronald J. Ilg Michael P. Gunter • i ~ The University of Texas at Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373 I UT Account No. le i I I• • • EXECUTIVE SUMMARY---RECOMMENDATIONS The purpose of these experiments with juvenile spotted seatrout and red drum is to establish a methodology of assessing the ability of fish acclimated to estuarine salinity levels to withstand short term ·stresses of increased or decreased salinity at winter 15°C and summer 28°C temperatures. The experiments ·were conducted by determining the metabolic • performance of the fish acclimated to 20 ppt salinity, which is near optimum, and then subjecting the fish to salinities of 10, 30 or 40 ppt salinity in order to follow their reactions and propensities to recover and readjust to the new salinity levels. For the red drum only a similar experiment was carried out except that the blood serum osmolality {as a measure of the degree of adaptabil·ity) was followed. For both kinds of experiments, the time course was followed by measuring at frequent intervals the metabolic or the blood osmolality levels for three-day periods. Metabolic performance was measured as the scope for activity, which is the difference between the respiratory metabolism at maximum sustained activity and at the lowest maintenance {standard) level• During the first hour or so the reaction phase to a salinity change usually was accompanied by an abrupt drop in the scope, followed by a variously extended low metabolic level stressed phase and then by a rising recovery phase at about 30 hours. By about 48 hours typically there was reasonable • • • stabilization phase, when scope was lowered, principally by • reduction in the active metabolic level and very little influenced by a change in standard level. For the first three hours after a salinity change, the • smaller the fish the greater was the decrease in metabolic scope. The greater the salinity change the greater the duration of the stressed phase and the length of time £or the initiation • of recovery phase. Temperature is relatively not important except at the upper (28°C) levels for the small fish, and possible at salinity extremes of 10 and 40 ppt for the red drum at both 28°C and 15°C where the active metabolic rates are about equal. In general, the sudden temporary stresses caused by• salinity changes are more severe than the steady state stresses at salinities far from optimum. However, ·this study indicates that it is possible to utilize the rapid salinity change • technique with small fish to assess their capabilities to become acclimatized to salinity changes. It would appear that rapid changes toward lower salinities, which also can occur • rapidly in nature, result in less stress than rapid chan.ge--s-: to progressively higher salinities, which ordinarily occur only slowly in nature. Rapid changes to higher salinities are a1so accompanied by osmolarity malfunctions in regulation and death -· in contrast to rapid changes to lower salinities that do not usually result in osmoregulatory problems and death. With the • various cautions discussed in the study, it appears that young fish do respond to rapid salinity changes in a way that is • • • indicative of similar, but slower, responses in the natural estuaries. Therefore it would appear reasonable to suppose that the methods of this study could be developed further for different species, different size ranges, seasons, and • other variables in relation to anticipated sal·inity changes• • • • ~· • • • • • • • • • • ~­ • INTRODUCTION NOTE-­ The materials in this report are taken directly from a Master's Thesis presented December 1979 by Mr. Michael Preston Gunter to the Faculty of the Graduate School of The. University of Texas at Austin in partial fulfillment of the requirements for the degree of Master of Arts. The thesis title is: "Studies on the Time Course of Acclimation to Salinity Changes in Juvenile Spotted Seatrout and Red Drum." The numbering of the figures and tables follows Gunter's thesis, which is largely paraphrased or quoted throughout• The purpose of this study is to characterize the rates of adaptability to salinity-temperature regimes by small red drum (Sciaenops ocellata) and spotted seatrout· (Cynoscion nebulosus), with particular reference to rates, or relative rates, of acclimatization to changing salinity gradients. Both species are important conunercially and recreationally, and both are generally euryhaline (Gunter, 1945), although the red drum probably spawn in the Gulf just outside passes (Simmons and Breuer, 1962). Earlier work on adults and subadults indicates that the optimal metabolic scope-salinity relationship is near 20 ppt (Wohlschlag and Wakeman, 1978; Wohlschlag, 1977) • Especially beyond 30 ppt, these authors have shown that the .metabolic scope and swimming performances drop rapidly• • • Kinne {1962) has noted that salinity at spawning times • may cause permanent nongenetic changes in morphology, growth rate, salinity tolerance, and metabolic responses. Kinne {1964) also notes that salinity per ~ influences the solubility • of oxygen, the ammonia to ammonium ion ratios, and the densities and viscosities. However, as Bern {1975) notes, from about 10 to 48 times the body area is gill surface, which is the • immediate surface of response to salinity changes or reg.:imes. The ionic and osmoregulatory problems of estuarine fishes are well known, but the variety of mechanisms and influencing •• circumstances are not always well understood. Conte {1969) reviews the marine teleost system of swallowing water and secr~ting accumulated salts at the gills or kidney. Urine • flow in marine teleosts is inadequate for water balance maintenance, and according to Maetz {1974), Parry {1966), among others, most salt excretion is extrarenal• • Particularly important are the so-called "chloride secretory cells" in the gills {Conte, 1969; Parry, 1965; Gordon, 1964). Gill permeability is largely endocrine-controlled by • hormones like prolactin {Sage, 1973; Sage and DeVlaming, 1975; • Johnson, et al., 1974), cortisol {Bern, 1975), and epinephrine {Isaia, 1979) • Maetz {1974) has summarized much of the research on high and low salinity adaptations by marine teleosts. Motais, et al. (1966) indicate that there are two types of euryhalinity: (1) • by control of plasma osmotic concentrations, and (2) by a • • tolerance of variation in plasma ion concentration or "cellular • • resistance" as in Fundulus spp. Temperature also influences salinity effects. Kirsch (1972) associated increase in temperature with urinary water and electrolyte excretion for ·the eel, while Mackay (1974) noted that at both upper and lower incipient lethal temperatures plasma sodium and chloride concentrations decreased. At a low.er. • • temperatures, at least, these lower concentrations may reduce ionic and osmotic regulatory energy requirements. The relationship of temperature and salinity has been • studied extensively by Kinne (1964) for a euryhaline cyprinodont fish, whose optimal growth occurred at optimal temperature of 25°C in both fresh and sea water. Brett (1976) has shown that the • optimum scope for activity and optimum growth rate for the sockeye salmon, while different conceptually, both occur at 15°C. Relationships between routine oxygen consumption rates • and salinity have been compiled by Nordlie (1978), who noterl that there are four general patterns depending upon degree of metabolic response to salinity and upon relation of metabolic • response to the serum isosmotic level. Wohlschlag and Wakeman (1978) noted that the spotted seatrout adults and subadults had minimal (standard) levels and maximal active levels, and accordingly the maximum scope, somewhat above the isosmotic level. The energy costs of osmoregulation are variously estimated • or measured. Potts (1954) indicated that theoretically at least the costs are quite small and may be easily masked by other • • factors • Rao (1968) had measurements to indicate that • osmoregulation was as high as 27% of all energy costs in terms of oxygen consumption; Farmer and Beamish (1969), as high as 29% • • The interpretation that osmoregulatory costs of Rae's (1968) trout can be added to the scope was suggested by Fry (1971) since Rao found that at all swimming velocities observed • the metabolic rate was always minimal near the isosmotic level (7.5 ppt), but only up to a salinity of about 15 ppt after which metabolic costs inc.reased relatively more for smaller • fish. Similar studies on mullet by Nordlie and Leffler (1975) and Collins (1974) indicate also that lowest standard rates are near _ the isosmotic points and standard rates tend to increase• both above and below 10-11 ppt until maintenance costs are about doubled at 45 ppt. Oxygen consumption at all velocities was lowest at the • isosmotic salinity of 11.6 ppt for the Tilapia nilotica studied by Farmer and Beamish (1969), who also found that exercised fish were less capable of maintaining constant plasma osmotic• concentrations than were unexercised fish. With a possible competition for energy allocation between ion-osmotic regulation and swimming, it is expected that the swimming velocities would • have to decline when salinities departed widely from those near isosmoticity (Wohlschlag and Wakeman, 1978), or altered blood osmolarities as in Tilapia (Rao, 1968; Fry, 1971). Interspecific • comparisons among fishes are difficult, whether their affinities • • 5 • are freshwater, estuarine or marine, whether their life history • operational modes are .resident, anadromous, or catadromous, all may have quite widely different relationships to salinity, even though all might be determined to be euryhaline• However diverse the salinity relationships may be to activity as was growth, and metabolism in general, ion­osmoregulation appears to be contolled by endocrines, particularly • prolactin and cortisol, and in£luenced by such environmental factors as temperature. At the present time, the great diversity ·of literature on thes·e subj·ects does not seem to provide any clear cut guidelines ·for predicting what happens when a particular species at a particular size or age range is subjected to a • particular salinity regime. More specifically, little is known about the time course of fish adaptations to salinity changes. Ventkataramiah, et al. (1977) in their studies of the time • course of brown shrimp adaptation to salinity changes found that metabolic and osmotic adaptation occurred faster at 25°C than at 18°C or 32·0 c. Three adaptation phases were: (1) i:rmnediate • responses, (2) stabilization, and (3) new steady state levels• • They found that there was a positive interaction of metabolic and osmotic responses at 25°C, but the interaction was inconsistent at more extreme temperatures. Temperature changes affected each ion independently, although ion regulation appeared to be generally temperature-dependent. Smaller shrimp appeared to • prefer higher salinities and lower temperatures. · Thus, the detailed study with the shrimp, appeared to have much in common • • with local studies on the red drum, spotted seatrout, and • other species in that spawning, hatching, developmental patterns, and subsequent life history stages would be normally suspected of eliciting different metabolic and metabolism­• related responses ·depending upon salinity• • • • • • • • • METHODS AND MATERIALS • Sources of Fish--Acclimatization From September 1978 through August 1979 small red drum • and spotted seatrout were captured either by seine or otter trawl in the vicinity of Port Aransas, Texas. Most individuals were taken from seagrass beds .near Marker 85 in the Lydia Ann • Channel. Small (1-2 g) red drum were also obtained from the Texas Parks and Wildlife Department redfish rearing ponds at Palacios, Texas, which permitted ·the use of small fish at • • 28°C, which would not have been possible otherwise, due to the fact that underyearlings during the summer in the field are in ·the 50-100 g weight range. After capture, fish were placed in thermally controlled holding tanks at the experimental temperature (15 or 28°C) and at 2.0 ppt salinity and held for at least three days. These fish were fasted the day before insertion into the respirometers, and oxygen consumption measurements were .not performed until the following day• • General Procedures Three physiological variables were monitored over a 72-hour period following salinity changes. These variables are: Active Metabolic Rate--the rate of oxygen consumption at given temperatures and salinities for a fasted fish swimming• at its maximum sustained swirruning speed • • • Resting Metabolic Rate--the rate of oxygen consumption at • • given temperatures and salinities of a fasted fish confined to a respiration chamber and shielded as much as possible from exogenous stimuli, e.g., light, noise, etc. Whole Blood Osmo1ality--mosm/kg--a measure o.f the osmotic pressure exerted by the blood as measured by the colligative • properties, e.g., vapor pressure, which change as a result of solute activity in the blood. Since vapor pressure depression is the variable measured here, the erythrocytes have no effect on the measurement.. (This variable was measured only for small red drum.) • These variables were measured one hour before the salinity changes and at 1, 3, 6, 12, 24, 30, 48, 54, and 72 hours after the change, except for the 20-40 ppt change in which the 1-hour• reading was necessarily omitted. Salinity changes studied were from 20 ppt to 10, 30, or 40 ppt. Responses to these changes were studied under winter (15°C) and summer (28°C) conditions • • Each experimental run consisted ideally of one determination of the active metabolic rate, four determinations of resting metabolic rate, and as many determinations of whole blood• osmolality as could be made with the number of fish on hand, usually 2-3, at each time interval. When the experimental fish (especially small red drum) lost weight during the 72 • hour "run", • • 9 weights were measured before and after the "run". Linear • weight loss over time was assumed, and interpolated values were used in metabolic rate determinations. • Metabolic Rate Measurements • Active Metabolic Rate--This variable was measured using the Wohlschlag modified Blazka respirometer, which has been described previously (Wohlschlag and Wakeman, 1978). Due to the generally small size of the juvenile fishes studied, a group (school) of fish of similar size were run simultaneously • in the apparatus. They were inserted into the chambers about 15 hours before the salinity change and allowed to adjust to the chamber overnight before any oxygen consumption readings were taken. The respirometer is fully temperature controlled (~ 1°C). Aeration during this period was provided by the flow through system described below. Oxygen consumption at • maximum sustained swimming speed was measured as the decrease in the partial pressure of oxygen (p02) during an interval of about 60 min. The p02 decrease was converted to mg02/hr-1 • allowing for the duration of the time interval, the oxygen solubility coefficient (Green and Carrit, 1967) at the appropriate salinity and temperature, the volume of the c~amber (207 1), and appropriate p0 2 to mg0 2 conversion factors. The • p02 of the water in the chamber was measured by injecting samples into a Radiometer E5047 oxygen electrode connected to • a Radiometer PHM-71 acid-base analyzer with a PHA930 p02 module. Following a 15-20 min. "warm-up" period the speed of the • • water flow in the chamber was increased by increments until • the relative steady propulsive swinuning wave of the fish began to show severe tail beat frequency aberrations commonly known as a shift to 'burst and glide" swimming. Experience has shown • that just below this speed is the maximum sustained swimming speed, or that which can be powered aerobically for 100-200 min. (Webb, 1975). This level was determined for each time • interval and is the level at which the active metabolic rate was measured. Because of the small size and the number of fish in the Blazka chamber, the maximum sustained velocity could be • slightly underestimated (see Discussion). Resting Metabolic Rate--To measure this rate, one to three fish were inserted into darkened 2.9 1 Fernbach flasks • immersed in a constant temperature water bath. These flasks were equipped with syringe ports in the stoppers and polyethylene tubing running to the central volume of the flask. A small • bleed hole in the stopper allowed water displacement when 3 ml samples were taken. Oxygen consumption measurement was performed in the manner described above, and at essentially the same time • • as the active metabolic rate. Aeration between readings was accomplished by removing the stoppers, and covering the tops of the flasks with netting. Convection, aided by airstones, in the water bath, provided mixing and aeration. • Blood Osmolality Blood osmolality was measured with a Wescor 5130B vapor pressure osmometer which requires only enough blood to saturate .. a 6 mm diameter filter paper disc. Due to the small size of • • 11 fish involved, a special technique _for vampirizing them was • developed. Individuals were removed from their holding container, rinsed with deionized water, and blotted dry. The tail was then severed posterior to the anus with a scalpel. • The anterior cross section was then blotted once to avoid contamination with intracellular fluid and the blood issuing from the caudal artery was soaked up by a small filter paper • disc which was immediately placed· in the osmometer. To facilitate bleeding, very small fish were spun at arms length for a few seconds ·to let centrifugal force take blood to the • posterior end of the fish. This entire procedure took less than one minute. • Salinity Changes • All salinity changes occurred at. the same rate of approximately 10 ppt hr-1. This was accomplished by the use of a 126 1 salinity change reservoir and a pump with tubing to • carry flow into the Blazka chamber (see Fig. 1). A return hose carried water back to the reservoir. By starting at a predetermined salinity in the reservoir, · the pump could be turned on causing water in the reservoir to cycle· with the water in the chamber. Equilibrium at the test salinity was reached in 50-60 min. For the changes from 20 to 40 ppt, the salinity· change occurred in two phases, the first from 20 to 30 ppt and the second from 30 • to 40 ppt. This procedure took 100-120 min. The running sea water of the lab was used in all experiments • • • • • Figure 1. Diagram of the 207 1 modified Blazka ·respirometer. · • M --variable speed motor I --impeller PS--posterior screen • ST--transparent acrylic swimming tunnel B --flow linearizing baffles CT--constant temperature water bath • ET--circular exercise tank SR--salinity change reservoir F --filter • P --pump IT--inflow tubing RT--return tubing • (Adapted from Wakeman and Wohlschlag, 1978) • • • • • • • • • • le • • • Salinities were adjusted by either dilution with deionized • water or by adding commercial sea salts. • Calculations Underyearlings used in this study ranged in weight from • 1 to 147 g. Because size is a critical factor governing the metabolic rate, a procedure to standardize all .data for weight was needed. Further, activity (swimming speed) is very important • as a controlling factor and although each active metabolic rate measurement was at the determined sustained velocity, there was variation in the nunber of lengths per second the • groups attained. To achieve standardization of the data and to evaluate the effect of the salinity change alone, a series of multiple regression analyses were performed using log average • weight (log WT) and average total lengths per second (TL· ·s~l) as independent variables and log mg02kg-1hr-1 (Y kg-1) as the dependent variable. The regressions then take the form: ~ = a + bw Xw + bv Xv where: Y= log mg02hr-l • a = a constant bw = partial correlation coefficient of average body wet weight • bv = partial correlation coefficient of velocity in average total lengths per second (TL s-1) Xw = log average weight (g) • Xv = velocity in TL s-1 This procedure was conducted for each species at each temperature • • • (See Tables 1 and 2 with relevant statistics in Tables 3 and 4 • in the next section.) Data selected for these regressions came from previous studies in this laboratory (Wakeman, 1978; Wohlschlag and Wakeman, 1978; and Ilg, 1979) as well as the • • present study. Using the partial correlation coefficients in these regressions, the actual active data were standardized for 10 g fish swimming at 4 TL s-1 using the following equation: A A Y' =YA+ (1-Xy,)•bw + (4-Xv)·bv where Y' is the standardized rate in log mg02hr-l, YA is the • actual rate in log mg02hr-1, and the other symbols have their ,... usual meanings. The standardized value (Y') was then converted • to mgo2~a-1 by taking the antilog and dividing by the standardized • weight, 10 g. The regression at 20 ppt for the species and temperature in question was used for standardization of active and resting data. These regressions were also used to calculate • the standard metabolic rate of a 10 g fish at the various temperatures and salinities. This procedure involved extrapolation to zero activity and is therefore similar to Brett's (1964) • method of estimating the standard rate. It differs in that a multiple regression involving weight as well as velocity was used and all values, rather than just the lowest ones, were • considered. The weight used in these calculations is 10 g, hence the standard metabolic rate is also standardized for a 10 g fish. Since the data represented by the multiple regressions in Tables 1 and 2 are for acclimated fish, the estimate of the standard rate is only possible at -1 and 72 hours, if the fish • • are assumed acclimated at the end of the experiment rate is • constant from the time of the salinity change to the 72-hour value of the standard rate was used for all post change calculations• • • Metabolic Scope for Activity This attribute is defined (Fry, 1947, 1957} as the difference between the active and standard metabolic rates • • Biologically, it is a measure of that energy which can be expended aerobically over and above maintenance costs of the organism. Metabolic scope can be used as a convenient measure • of sublethal stress (Wohlschlag, 1977). In the present experiment, stress caused by rapid salinity changes is monitored over time so that the timing -of the stress and the rate at which it diminishes can be observed• • ·• • • • 17 RESULTS • Preliminary Regression Calculations The spotted seatrout and red drum regressions relating• log oxygen consumption rates to log weights and swinuning velocities at 15°C and 28°C are in Tables 1 and 2, respectively. The corresponding statistical data are in Tables 3 and 4,• respectively. • Metabolic Responses The metabolic data for the spotted seatrout and red drum are in Tables 5-10 for the various salinity changes and temperatures. When subjected to • rapid salinity changes, the juvenile fishes studied showed metabolic stress responses which began almost inunediately. In the majority of cases, - stress, as measured by a decrease in metabolic scope, continued • to become more severe and reached a critical level (scope minimum) between 6 and 24 hours after the change (see Figures 2-13). Generally, the minimum level is either maintained for -· several hours or a single critical point is immediately followed by a period of recovery which lasted between 12 and 24 hours after the critical time period. This phase is followed by a period characterized by relative stability. The pattern described above hold for all except the 20 to 30 ppt change for red drum (Figures 9 and 12). At both • 15 and 28°C, this change caused similar responses in the time course. Initially, there was a decrease in scope, and the critical point occurred about· one hour after the salinity change • • '% ~ ~ N :::> UJ ;:;; < I­ ::> "M I­ ~ co ~ " V> ti) < ~ ll") x -<( UJ UJ I->< u u.J u.. z I­ UJ 0 V)~ Ci >-<( Vl I-U.I '.!.) v; QI! z :( UJ 02 CJ(!> < <: z ~ I­ :::> :u.i °'0 iE g_ Table 1. Multiple regressions relating expected log oxygen consumption rate (Y) to log body weight (Xw) , A and ~ -1 . velocity (TL s ) at experimental temperatures and salinities. Spotted seatrout. Eqtiatioh Standardized Equation Temp. Standard Rate number oC yA = a + bw xw + b. x mgo 2 kg-1 hr-1 v v .;'\ S281 20 y = -.663 + .990 xw + .126 xv 2li.1 S282 28 y = -.542 + .969 x + .124 x 267.0 w v S283 28 yA = -.486 + .920 x + .114 x 277.1 w v ~ S284 28 y = -.368 + .e15 xw + .113 xv 321.5 Sl51 15 y = -.879 + 1.005 xw + .126 xv 133.6 ~ w v Sl52 15 y = -.860 + .985 x + .172 x lJj.2 "' ,_. Sl53 15 y = -.728 +. .973 x + .140 x 176.l co .w v Sl54 15 y" = -.726 + .982 xw. + .120 xv ieo.3 Table 2. Equation number R281 R282 R283 R284 Rl51 Rl52 Rl53 Rl54 Multiple ~egressiohs relating expected log oxygen consumption rate (Y) to iog body weight (X ) ; and w . -· -1 . . velocity (TL s ) at experimental temperatures and salinities. Red drum. Eqttation Standardized Temp. Standard Rate oc J\ y = a + b ingokg-l hr-l w xw + bv xv 2 / . /";'" A . . . 28 y = -.978 + 1.046 xw + .154 xv 117.i "' . . 28 y = -.698 + .935 xw + .148 xv 112.5 ,.. 28 y = -.667 + .894 xw + .162 xv 168.6 28 "y = -.559 + .906 xw + .116 xv 222.2 15 Y = -.954 + 1.088 xw + .138 xv 136.0 15 y" = -.765 + .g49 x + .145 x 152.5 w v " , 15 y = -.715 + .959 xw + .135 xv 175.l ,......, 15 2 = -.964 + 1.i20 x _ + .153 x 146.l w . v \.0 • • • Table 3. Multiple regression statistics for equations in Table 1. Spotted seatrout. Co.efficient of ·Standard dev.iations• Equation N Determination and Probabilities number R2 Sy sbw s.bv 5151 .20 o. ·967 0.•0480a 0.0073a 0. 012Sa · • 25 0.852 0.1249a 0.0179a O. 041·7a 5152 5153 l.8 0.816 0 •. 2355a 0.0069a 0.0825ns 5154 20 0.962 o·. 0563a O.Ol.13a O.Ol64a • 5281 .25 0. 93·7 0.0530a 0.0076a o.000oa .5282 19 0.992 0.0722a O.Ol03a O.Ol69a 18 0.971 O.l264a o. or1oa O.Ol96a • 528~ 5284 .22 0.982 0.0320a 0.0060a 0.006la • a--p< O. 01 ns--not significant at 0. 05 level • • • • 21 • • Table 4. Multiple regression statistics for equations in Table 2. Red drum• Coefficient of Standard deviations Equation N Determination and Probabilities• number R2 Sy . sbw sbv RlSl 19 0.978 O.OSlSa 0.0099a O.Ol90a Rl52 30 0.975 0.0847a 0.0064a 0.0177a • Rl53 20 0.960 0.2437a 0.0349a 0.074lns Rl54 .21 0.963 O.l603a 0.0214a 0.043Sb • R28l J.6 0.979 0.077la O.Oll7a O.Ol97a R282 .15 0.994 0.1979a 0.0014a 0. O_lSOa R283 14 0.969 0.1484a 0.0208a O·.·0279·a R284 17 0.987 0.0669a 0.0064a 0.0093a • • a--P< 0. 01 b--0 • 01 < p <. 0 • 0 5 ns--not signi£icant at O. OS 1evel • • ' . 22 Table 5• Time course of resting and 10-g standardized oxygen • consumption rates. Spotted seatrout• • Salinity Time From Average Resting Standardized Temp.• Change Change Weight N Rate Rate oc ppt hl:s g mg02kg-lhr-1 mgokg-lhr-l • 2 28 20-10 -1 8.684 19 337.7 336.2 1 15.l 4 347.0 351.5 • 3 15.l 4 276.3 279.9 • 6 15.l 4 237.2 240.3 12 15.1 4 403.6 408.8 24 15.1 4 247.2 250.4 30 15.1 · 4 217.3 220.1 48 15.l 4 301.5 305.4 • 54 15.1 4 199.1 201.7 72 15.5 3 202.5 205.3 28 20-30 -1 8.684 19 337.7 336.2 • 1 5.711 7 373.1 366.7 3 5.696 7 392.5 385.7 6 5.300 5 318.0 311.8 • 12 6.296 6 402.9 397.1 24 5.539 7 266.1 261~3 30 10.773 3 229.7 230.2 48 10.433 3 282.8 283.2 54 10.367 3 303.3 306.6 72 10.03 3 340.7 340.7 23 Table 5 . (cont.) • Salinity Time From Average Resting Standardized • Temp. Change Change Weight N Rate Rate oc ppt hrs g mgo2kg-lhr-l mgo2kg-lhr-1 28 20-40 -1 8.684 19 .337. 7 336.2 • 3 8.013 8 314.6 312.4 6 7.429 7 349.1 345.9 • .12 8.013 8 336.2 333.9 24 7.938 8 383 380.3 • 30 7.925 8 339.2 336.8 48 7.87'5 8 323.2 320.8 54 8.371 7 292.6 291.0 15 20-10 -1 15.6 25 .139.5 146.5 • 1 10.1 8 155.4 155.6 3 .10.1 8 135.1 135.2 • 6 10.1 8 209.3 209.5 12 10.1 7 149.8 150.0 24 10.0 8 134.6 134.6 30 9.9 8 168.5 168. 3 ·. 48 9.8 8 132.6 132.3: 54 9.7 8 123.0 122. 6 . 72 10.9 4 96.1 97.0 24 Table 5. (cont.) • Salinity Time From Average Resting Standardized • Temp. Change Change Weight N Rate Rate oc ppt hrs g mgo2kg-lh~-l mgo2kg-lhr-1 15 20-30 -1 15.6 25 139.5 146.S • 1 13.4 11 .134. 2 138.6 3 13.2 12 161.3 166.3 • 6 13.2 12 135.6 139.8 • 12 1'3 •. 2 12 143.8 148.3 .24 13.2 12 109.3 112.7 30 13.2 12 126.1 130.0 • 48 13.1 11 110.0 113.3 54 13.1 12 .149.7 154.2 72 13.1 12 122.l 125.8 15 20-40 -1 15.6 25 139.5 146.5 3 27.6 6 115.0 128.6 • 6 27.6 6 155.7 174.1 12 30.2 5 173.2 195.5 24 18.5 4 114.8 122.8 • 30 18.4 4 98.0 104.7 48 18.1 4 119.1 127.1 54 18.0 4 112.2 119.7 • • 72 17.7 4 133.0 141.6 25 Table 6. Time course of resting and 10-g standardized oxygen • consumption rates. Red drum• • Salinity Time From Average Resting Standardized Temp. Change Change Weight N Rate Rate oc ppt hrs q mgo2kg~lhr-l mgo2kg-lhr-l • 28 20-10 -1 15.36 18 381.0 383.5 l 2.11.3 4 520.l 507.9 • 3 2.113 4 437.7 427.5 6 2.275 2 543.7 531.6 • 12 2.038 4 473.• 9 462.6 24 1.. 963 4 568.3 554.4 30 1.867 3 479.7 467.6 48 1.800 4 491.1 478.4 • 54 1.775 4 506.2 493.l 72 1.650 ·4 589.0 573.1 28 20-30 -1 15.36 18 381.0 383.5 • 1 14.044 8 447.0 449.3 3 14.019 8 411.4 413.5 6 9.579 7 366.5 366.3 • 12 15.657 7 339.2 341.5 24 13.781 8 384.0 385.9 30 13.700 8 333.7 335.3 • 48 13.525 8 429.8 431.8 54 13.293 7 437.5 439.4 • 72 14.903 7 386.4 388.8 • .,., Table 6 • (cont.) • Salinity • Temp. Change oc ppt • 28 20-40 15 20-10 • • • 15 20-30 • Time From Change hrs -1 3 6 12 24 -1 1 3 6 12 24 30 48 54 72 -1 1 3 6 12 24 30 Average Weight g 15.360 22.443 22.429 .30. 7.3 25.846 3.36 -3.83 3.65 3.82 3.84 .3.76 3.79 3.71 3.68 3.61 3.360 1.540 2.405 2.825 2.450 2.720 2.940 N 18 7 7 5 6 34 12 11 12 11 12 11 12 12 11 34 11 10 8 11 9 8 26 Resting Standardized Rate Rate mg02kg-lhr-l mgo2kg-lhr-1 381.0 383.5 3.52. 9 357.3 373.2 377.8 268 •. 1 272.1 325.6 330.3 214.0 206.3 182.0 176 .2 229.2 221.5 153.1 148.2 234.7 227.3 191.2 185.0 205.8 199.2 203.4 196.7 167.9 162.3 184.3 178.1 214.0 206.3 246.0 231.0 224.6 214.l 245.7 235.5 213.3 203.4 186.3 178.3 169.1 162.3 27 Table 6. (cont.) •­ Salinity Time From Average Resting Standardized • Temp • Change Change Weight N Rate Rate oc ppt hrs g mg02kg-lhr-l mg02kg-lhr-1 • 48 2.305 11 249.4 237.4 54 2.220 12 203.9 193.8 • 72 2.580 9 197.7 188.9 15 20-40 -1 3.36 34 214.0 206.3 3 3.75 12 187.0 180.9 6 3.79 12 184.l 178.2 • 12 3 .78 11 J.90.4 184.3 24 3 .• 65 12 255.8 247.3 30 3.66 12 158.5 153.2 • 48 3.48 11 190.9 184.2 54 3.72 10 170.3 164.7 72 3.-45 12 193.3 186.5 • • • • ,· ..• • • • • • • • • • .. " I " Table 7. Time course of active and 10-g, 4 TL/S standardized oxygen consumption rates. • Spotted seatrout. Average lOg-4 TL/S Salinity Time No. Total Average Active from of Standardized Temp. Change Change Fish Length Weight Velocity Rate Rate oc. ppt hrs cm g TL/S mgo2kg-lhr-l mgo2kg-lhr-l 28 20-10 -1 J 21.17 13.11 3.670 889.9 1088.8 1 22.8 106.0 4.009 780.8 936.6 1 3 21.17 73.77 3.670 650.3 795.7 1 22.8 106.0 4.009 814.7 977.1 3 3 21.11 73.77 3.670 700.4 856.9 i 22.8 106.0 4.009 678.9 814.2 6 3 2i.i7 73.77 3.670 574.7 703.1 1 22.8 106.0 4.009 733.9 880.3 12 3 21.17 73.77 3.238 537.3 699.5 1 22.8 105.0 4.009 599.7 718. 5 . 24 2 20.60 \ 66.65 3.771 503.8 602.7 .' 1 22.8 104.0 4.009 641.3 767.6 t\J ,,. 30 2 20.6 66.65 3.771 785.2 839.8 1 22.8 104.0 4.009 618.3 740.2 I 48 2 20.6 66.65 3.771 664.4 794.7 1 22.8 102 4.009 651.2 777.5 54 2 20.6 66.65 3.771 647.0 775.0 1 22.8 101.0 4.009 746.4 891.9 72 2 20.6 66.65 3.771 647.8 775.0 1 22.8 100.0 4.009 811.8 968.7 20-30 -1 5 11.3 11.9 3.438 945.6 1038.2 7 12.6 15.5 5.078 817.2 723.5 1 5 11.3 11.9 3.438 969.4 1064.3 7 12.6 15.5 5.078 661.4 585.5 3 5 11.3 11.9 3.438 908.3 996.5 7 12.6 15.5 5.078 ·757 .1 670.3 6 5 11.3 11.9 3.438 . 772.4 846.8 7 12.6 15.5 5.078 648.1 573.8 12 5 11.3 11.8 3.438 642.9 708.4 7 12.6 15.5 5.078 911.6 807.0 N \..0 I, 24 30 48 54 72 20-40 -1 3 6 12 24 5 4 5 4 5 4 5 4 5 4 7 7 7 7 7 7 7 7 7 7 • 11.3 13.2 11.3 14.4 11.3 14.~ 11.3 14.4 11.3 14.4 9.6i 10.33 9.61 10.33 9.61 10.33 9.61 t0.33 9.61 10.33 • 11.8 i6.8 ,11.8 2i.65 11.7 21.65 11.7 21.65 11.6 21.65 7.83 B.61 1.11 I 8.61 7.10 B.61 7.59 8.61 7.33 8.61 3.438 4.847 3.438 5.078 3.438 5.078 3.438 5.078 3.438 5.078 3.804 3.3i8 3.567 3.318 3.804 3.318 3.804 3.539 3.804 3.539 • 676.4 1064.0 975.3 979.6 1199.B 778.2 1154.2 959.9 1172.8 920.7 843.6 939.3 613.4 961.3 587.4 862.6 761.9 1119.2 715.3 780.4 • • 687.8 979.1 1067.5 891.0 1315.4 707.7 1263.1 873.1 1285.4 837.5 850.9 1026.1 641.1 1049.l 592.7 941.2 767.2 1181.8 718.4 825.0 w 0 • 30 7 9.61 7 10.33 48 7 9.61 7 10.33 54 7 9.61 7 10.33 72 7 9.61 7 10.33 • 7.21 8.61 6.84 8.61 6.71 8.61 6.33 8.61 3.804 3.539 3.804 3.539 3.804 3.539 - 3.539 • 775.3 1096.4 797.7 862.6 659.3 834.6 - 842.6 • 777.9 1063.8 854.5 911.7 657.7 822.2 890.5 • w I-' ,. ' • • • • • • • • • -t- Table 8. Time course of active and 10-g, 4 TL/S standardized oxygen consumption rates. Spotted seatrout. Temp. oc. 15 Salinity Change ppt 20-10 Time from Change hrs -1 1 3 6 No. of Fish 4 7 6 4 7 6 4 7 6 4 1 6 Average Total Length cm 13"25 10.16 13.05 13.25' 10.16 13.05 13.25 10.16 13.05 13.25 10.16 13.05 Average Weight g 17.6 8.44 17.7 17.6 8.43 17.7 17.6 8.43 17.7 17.6 8.40 17.7 Velocity TL/S 3.-713 3.834 3.456 4.177 3.632 3.456 9.177 3.632 3.456 4.177 3.834 3.456 Active Rate mg02kg-1hr-1 545.4 697.4 618.5 550.8 442.7 350.5 459.8 464.9 370.2 539.5 311.3 385.5 • lOg-4 TL/S Standardized Rate mgo2kg-lhr-l 616.4 743.0 774.3 518.2 510.5 438.4 432.7 536.0 463.1 507.5 331.6 w I\) 482.1 .... ~ 12 4 13.25 17.6 4.177 513.0 482.1 7 8.37 3.834 459.2 489.l 6 17.7 3.456 382.4 478.5 10.16 13.05 24 4 17.6 4.177 514.8 483.4 13.25 7 8.31 3.834 602.5 642.7 6 17.7 3.456 362.6 453.7 10.16 13.05 30 4 17.6 3.249 252.1 341.6 13.25 7 8.28 3.834 468.0 498.0 6 17.7 3.456 415.1 519.5 10.16 13.05 48 4 17.6 4.177 529.5 496.9 13.25 1 10.16 8.18 3.834 464.0 494.6 6 17.7 3.456 346.4 446.2 13.05 54 4 17.6 4.177 575.5 540.9 13.25 7 8.16 3.834 486.5 518.2 10.16 6 1·3. 05 17.7 3.456 408.1 510.3 72 4 13.25 17.6 4.332 568.1 499.8 7 10.16 8.06 3.834 492.5 524.5 6 13.05 17.7 3.456 20-30 -1 6 10.2 7.8 3.6176 723.4 842.3 6 11.9 12.6 4.1344 565.l 536.2 w w • ·'" 1 3 6 12 24 30 48 54 72 20-40 -1 3 • 0 6 6 6 6 6 6 6 6 6 6 6 6 5 6 5 6 5 6 6 3 6 3 • 10.2 11.9 10.2 11.9 10.2 11.9 10.2 11.9 10.2 11.9 10.2 11.9 10.2 12.0 10.2 12.0 10.2 12.0 10.3 19.4 10.3 19.4 • 7.8 17.6 7.8 12.6 7.8 12.6 7.8 12.6 7.7 12.6 7.7 12.6 9.1 13.2 9.1 13.2 9.0 13.2 9.00 49.80 8.93 49.8 3.6176 4.1344 3.6176 4.3067 3.6176 4.3067 3.6176 4.3067 j.6176 4.3067 3.6176 4.1344 3.6176 .4.2708 3.6176 4.1000 3.8186 4.2708 3.1844 2.642 3.1844 2.642 • 537.65 600.151 615.3 527.7 362.8 596.3 364.4 437.2 441.4 326.7 410.2 400.81 595.5 516.7 501.9 543.0 545.i 582.8 572.4 270.6 492.1 191.7 • • 624.7 569.5 714.9 467.6 420.7 528.3 420.7 387.4 511.6 289.4 242.9 380.2 700.0 388.4 580.8 436.7 581.8 438.0 789.8 475.2 w ti:::.. 679.0 336.7 .,~ 6 6 3 12 6 3 24 5 3 30 4 3 48 4 2 54 4 2 72 3 2 • 10.3 19.4 10.3 19.4 10.0 19.4 10.0 19.4 10.0 19.l 10.l 19.1 10.4 19.l 8.87 49.8 I 8. 75 49.8 8.28 49.8 8.80 49.8 8.225 52.1 8.05 52.i 8.27 52.1 • 3.1844 2.642 3.1844 2.642 3.28 2.642 3.28 2.642 3.28 2.683 3.25 2.683 3.15 2.683 • 361.0 303.9 385.4 239.6 463.0 285.4 406.6 307.7 508.4 317.6 503.15 323.7 357.3 • 497.9 533.7 531.7 420.9 614.3 79.3 723.l 540.5 674.5 549.2 675.3 559.8 617.8 • w Ul • ,/ , Table 9. Time course of active and 10-g, 4 TL/S standardized oxygen consumption rates. • Red drum. Average lOg-4 TL/S Salinity Time from No. of Total Average Active Standardized Temp. Change Change Fish Length Weight Velocity Rate oc. -1 -1 ppt hrs cm g TL/S mgo2kg hr mg02kg-lhr-1 28 20-10 -1 33 6.12 1.985 6.347 1477.8 597.7 1 24.8 147.5 3.685 594.7 788.8 33 1 6.12 1.9788 6.347 1322.4 637.8 1 24.8 147.3 2.685 558.3 740.8 3 33 6.12 1.9667 6.347 887.0 561.4 1 24.8 147.0 3.685 575.9 386.7 6 33 6.12 1.9515 6.347 854.5 482.7 1 24.8 146.5 3.685 466.2 192 12 33 6.12 l.9182 6.347 909.5 444.2 1 24.8 145.4 3.685 395.9 109.1 24 33 6.12 1.8545 6.347 1014.5 550.l 1 24.8 143.3 3.685 522.3 691.7 w 30 33 6.12 1.8212 6.347 1004.2 455.6 °' 1 24.8 142.3 3.870 408.l 507.3 • ,. 48 54 72 20-30 -1 1 3 6 12 24 30 • 33 1 33 1 33 1 1 37 1 37 1 37 1 37 1 37 1 37 1 37 • 6.12 24.8 6.12 24.8 6.12 24.8 18.7 6.235 18.7 6.235 18.7 6.235 18.7 6.235 18.7 6.235 18.7. 6.235 18.7 6.235 1.7212 139.2 '. 1.6879 138.1 1.5848 135.0 67.5 1.81 67.4 1.81 67.3 1.805 67.1 1.797 6"6. 8 1.7811 66.2 1.7486 65.9 1.73 • 6.347 3.685 6.347 3.685 6.347 3.685 3.421 4.764 3.421 4.764 3.421 4.764 3.421 4.764 3.421 5.131 3.421 5.131 3.421 5.131 • 1351.4 480.9 1033. 467.2 1017. 355.4 636.l 1125.8 580.1 815.9 565.6 1240.7 744.5 1150.8 641.0 1352.6 659.8 916.4 722.0 1002.1 • • 541.5 635.8 413.7 617.3 405.3 468.9 877.8 774.2 799.9 562.6 780.2 855.2 1026.8 793.l 833.9 822.2 909.1 556.3 994.5 607.8 w ....,J .­ .. \ 48 1 18.7 65.0 3.421 614.9 846.3 37 6.235 1.68 . 5 .131 1489.2 901.9 54 1 18.7 64.7 3.421 774.8 1066.1 37 6.235 1.67 4.764 1330.2 912.2 72 1 18.7 63.8 3.421 698.6 1129.7 37 6.235 1.62 4.764 1072.3 734.1 -1 2 17.6 65.5 5.193 822.5 619.3 31 6.03 1.02 6.063 1444.0 640.7 3 2 17.6 65.5 5.193 641.4 482.4 31 6.03 1.79 6.063 896.2 396.6 6 2 17.6 65.5 5.193 641.4 482.9 31 6.03 1.76 6.063 12 2 17.6 65.5 5.193 533.4 401.6 29 6.03 1.70 6.063 1273.4 561.6 24 2 11.6 65.5 5 .. 193 579.1 436.0 20 6.03 1.59 6.063 1201.5 527.6 30 2 17.6 65.5 Dead 18 6.03 1.35 6.063 1418.6 697.6 48 \-Dead Dead w OJ .-. . . . Table 10. Time course of active and 10-g, 4 TL/S standardized oxygen consumption rates. • Red drum. Average lOg-4 TL/S Salinity Time from No. of Total Average Active Standardized Temp. Change Change Fish Length Weight Velocity Rate Rate 1 -1 oc. ppt hrs cm g TL/S mgo2kg-hr mg0kg-1hr-l 2 15 20-10 -1 17 6.48 2.56 4.745 1150.5 835.8 19 6.48 2.44 4.429 109.3 571.5 7 9.39 9.171 4.585 610.3 499.8 1 17 6.48 2.56 4.745 843.6 612.9 19 6.48 2.43 4.429 340.4 274.2 7 9.39 9.1 4.366 568.l 500.3 3 17 6.48 2.56 5.062 713.l 466.0 19 6.48 2.43 4.429 692.l 557.5 7 9.39 9.04 4.366 452.3 398.2 6 17 6.48 2.56 5.062 394.9 258.1 ' 316.3 19 6.48 2.42 5.694 599.4 w 7 9.39 4.366 517.1 454.9 8.94 l..O 12 17 19 7 24 17 19 7 30 17 19 7 48 17 19 7 54 17 19 7 72 17 19 7 • 6.48 6.48 9.39 6.48 6.48 9 .59 6.48 6.48 9.39 6.48 6.48 9.39 6.48 6.48 9.39 6.48 6.48 9.59 2.56 2.40 8.76 2.56 2.36 8.37 2.56 2.34 8.21 2.56 2.28 7.60 2.56 2.27 7.41 2.56 2.21 6.84 • 5.062 5.062 4.366 4.745 5.062 4.366 5.062 4.745 4.366 5.062 5.062 4.366 5.062 5.062 4.j66 5.062 5.062 4.366 • 561.1 518.3 552.0 723.1 843.l 479.4 633.8 567.1 565.5 611.2 670.l 420.8 533.l 551.7 668.5 651.7 555.l • 366.7 337.7 485.l 525.4 548.9 420.3 414.2 410.3 . 495.0 399.4 435.4 275.0 345.6 480.7 426.8 422.8 481.7 • .a:::. 20-30 -1 15 5.43 1.46 4.91 1326.9 890.6 . 17 5.18 1.13 4.83 18 5.79 1.82 4.18 628.3 511.9 1 15 5.43 1.46 4.91 749.3 502.9 17 5.18 1.13 4.60 572.4 418.3 18 5.79 1.87 3.89 335.6 318.9 3 15 5.43 1.46 4.91 856.3 574.7 17 5.18 1.13 5.14 858.6 523.9 18 5.79 1.811 4.04 954.1 862.l 6 15 5.43 1.45 4.91 1498.6 1005.7 17 5.18 1.12 5.14 1438.4 880.8 18 5.79 1.81 3.89 1183.1 1124.0 12 14 5.45 1.52 4.89 1031.9 690.4 17 5;18 1.12 5.14 1414.8 866.3 18 5.79 1.79 3.89 664.4 630.8 24 14 5.45 i.52 4.99 814.6 549.6 17 5.18 1.11 5.i4 1453.7 888.3 18 5.79 1.76 3.89 683.5 648.4 30 14 5.45 ·, 1.52 17 5.18 i.11 s.14 844.1 515.8 ~ ,_, 18 5.79 1.74 3.89 876.6 831.1 • ,• .' , - ... 48 12 5.54 1.66 4.81 1123.2 780.3 17 5.18 1.10 5.14 1156.1 704.9 18 5.79 1.69 3.89 1123.21 1063.2 54 12 5.66 i.62 ­ 17 5.18 1.09 5.14 1661.7 1016.6 18 5.79 1.68 3.89 1057.3 1000.5 72 12 5.66 1.62 4.71 1019.7 730.8 15 5.18 1.0 5.14 18 5.79 1.63 3.89 527.4 498.4 20-40 -1 25 6.22 2.07 4.944 677.6 455.6 9 8.48 4.94 4.351 726.7 623.2 25 6.39 2.20 4.170 706.4 617.4 3 25 6.22 2.06 4.614 367.1 275.6 9 8.48 4.93 4.110 480.4 446.6 24 6.39 3.30 4.110 579.8 506.6 6 25 6.22 2.05 4.614 415.8 312.2 9 8.48 4.93 4.351 427.8 366.9 24 6.39 2.19 4.170 492.5 430.3 12 24 6.22 2.03 4.944 413.8 277.3 9 8.48 4.91 3.868 382.9 385.8 ~ t\J 24 6.39 2.158 4.170 449.2 392.2 < ,• ,.y . 0 ,.. 24 23 9 24 30 23 9 24 48 23 9 23 54 23 9 23 72 23 9 23 • 6.23 8.48 6.39 6.23 8.48 6.39 6.23 8.48 6.39 6.23 0.40 6.39 6.23 8.48 6.39 1.99 4.89 2.1125 1.97 4.88 2.09 1.91 4.83 2.02 1.89 4.82 2.00 1.83 4.78 1.92 • 4.936 3.868 4.170 4.936 3.868 4.170 4.936 4.110 4.170 4.936 4.110 4.170 4.936 4.35i 4.170 • 692.9 556.7 420.0 591.9 527.5 549.4 627.0 537.4 444.B 594.4 595.8 572.9 579.7 601.3 596.0 • 466.4 560.8 366.2 398.1 67.0 478.8 421.1 499.0 387.0 398.9 553.l 498.0 388.4 514.8 517.3 • ~ w • 1400 a z 0 • 1200 . i= ~ 1000 ~~ V) '..c: 800 • yI--..-I I z;-01 87 600 &1 z.o 400 .-4 td E . ~ _._ __ -~---A--__ .,.__ -· >-200 x • 0 b • soc ~ J (.,.­ w .c:: ·~· Cl.~07 600 '•""• / o~ •· u . C\l • g 400 V) 0 2001 • -1i36 12. 2.4 30 48 .54 72. Tr M E (hours) • Figure 2. Spotted seatrout 2s0 c, 20-10 ppt.--(a) Time course of • active (4 TL/s) , and A resting (O TL/s) oxygen consumption following a one • hour salinity change from 20 to 10 ppt stan-· dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. (b) Time course of • metabolic scope for activity• • • • • • • • • • • • • z 0 t:= a. ~~ VJ~ z;:o a~ u. z c5'1 l.:J 0 ­ x 0 ...... It- w.::: a..~07 . o~ u C\J tfJ 0 g Figure 1400 a 1200 1000 --­800 }-I--YI 600 400 • •..__ __ ~-.--.-~._• -._._•. 200 b 800 _,,,,,,. • ... • I 600 .\_.---· • 400 2.00 _, i3 6 12. 24 30 4854 72 Tl ME (hours) 3. Spotted seatrout 2a0c, 20-30 ppt.--(a) Time course of • active (4 TL/s), and 6. resting (O TL/s) oxygen consumption following a one hour salinity change from 20 to 30 ppt stan­dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. (b) Time course of • metabolic scope for activity. • --..z 1400 a• -0 12.0 • 800 600 400 .__.. _ _±..-A___._ .... --~ • 200 b • 800 • 600 \;·~./-----·""'-----· • 400 2.00 • ,-1 3 6 iZ 24 30 48 54 72 Tl ME ( h.our-s) • Figure 4. Spotted seatrout 2a0 c, 20-40 ppt.--(a) Time course of • active (4 TL/s), and A resting • (O . TL/s) oxygen consumption following a two hour salinity change from 20 to 40 ppt stan­ ' dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. {b) Time • course of • metabolic scope for activity. • • • • • • • • • • • • z Q ~ ;'it. (Ji~ Z101 87 ---~­ ~g >­ x 0 Figure 1400 a 1200 1 000 800 600 --·­ ----;!~ 400 zoo • -_.,_ -.-.... --~------::6 b 800· 600 ------·, ,,,,,.·----... ........---· -............_-------· 2:00 I I -1i36 12 2.4 30 4854 72. Tl ME (hours) 5. Spotted seatrout is0 c, 20-10 ppt.--(a) Time course of • active (4 TL/s), and A resting (0 TL/s) oxygen consumption following a one hour salinity change from 20 to 10 ppt stan­dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. (b) Time course of • metabolic scope for activity• • 48 1400. a • z .. 0 1200 i= a.. .. ~.. 1000 V1 J: .. .. 800 ... • '­z;:o ~... ­ .... t · s~ 600 T -~ Zo cJL -.. ~.~E 1 400.. 1-I----f-I. ~E .. >-2.00 7·--z. --. -.­0 • • x -~ I:"* r-~ --• T -·­b 800.. ~ ''--~ w~ .600 ·0..70, 41 o~ ~ ~­ u C'J 400... <.1' 0 . • • \•· g ~. •---------· .. 2:00 . •. ' I I • I I -113 6 12. 2.4 30 4854 72. TIME (hours) • • Figure 6. Spotted seatrout 1S0c, 20-30 ppt.--(a) Time course of • active (4 TL/s), and A resting (O TL/s) oxygen consumption following a one • hour salinity change from 20 to 30 ppt stan­dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. (b) Time course of metabolic scope for activity• • • • .. ··-z Q 140O· a t- a... 12.00­ :2 ::> 7c.. 1000.. V'J ~ • . z ....· 0 ICJ . 800· C\J ~ ------a -··· -60 O· ~ • u~ . . :~---i--t/'I J-I CT °' .. -, .. • 6 2.00-~ ~.,._ ..... _---------.. A A 6. A A . • b 800.... 600. I• ·• •· 400 . / ·-­ • ~ \ ·-·............. ~· • ·­ 2.00-~ . . . I • -1 3 6 12. 2.4 30 48 54 72. If ME (hours) • Figure 7. Spotted seatrout 1S0c, 20-40 ppt.--(a) Time course of • active (4 TL/s), and A resting (O TL/s) oxygen consumption following a two • hour salinity change from 20 to 40 ppt stan­dardized for a 10 g fish. Dashed line is calculated standard metabolic rate. (b) Time • course of • metabolic scope for activity. • • • • • • • • • • • • a 1400i 12001 1 oool 800 6001 1 400~· ~ooL . Ii--..,.____________________________________.,. b 800' I I -1 i3 6 12. 2:4 30 48 54 72. r1 ME (hours) Figure 8•. Red drum 2a0 c, 20-10 ppt. ---(a) Time· course of •active (4 TL/s), and• resting (O TL/s) oxygen consumption following a one hour salinity change from 20 to 10 ppt standar-· dized for a 10 g fish.. Dashed line is cal­culated standard metabolic rate. (b) Time course of •metabolic scope for activity. • ,. z Q r- a_ • ~~ V1 '..c z~ 87 z~ w or C.!J E • >­ x a • ,... ''­ UJ.: a..~ • a~ u C\L ui a ~ • 1400-a 1200 . 1000 aoa YI-I . ~~ r1 600 400 A A. A ~ • zoo ~__....-._._... ._. ......... ._ _._, ._. _..... --._.. -· aoo .. ;·----. ·b /"'-. 600 • i ~/ 400 2:00 -1 r3·5 . 1Z 4854 7Z rtME (hours) Figure 9. ~drum 2a0 c, 20-30 ppt~.--(a) Time course of• active (4 TL/s), and&, resting (O TL/s) .oxygen. consumption following a one hour • salinity change from 20 to 30 ppt standar­dized for a 10 q fish. Dashed line is cal­ culated standard metabolic rate·. (b) T·ime • course of • metabolic scope for activity• • • 52 • 1400.. a I• 12.00 .. 1000, -~ 800.. • ·~ 600.. --\ 400.. ~ t:-I I 4 mortality >50°/o .. 4 • 2.00. ----.-. ---.-. -·-·-. ._ -----­b • 800.... 600... • 400.... \ 2.00..... \•.....--• . I I I I • -r 36 1Z Z430 72. IIM E (hours·) • Figure 10. Red drum 2s 0 c, 2·0-·40 ppt.--(a) Time course • o:f • active ( 4 TL/s) , and ~ resting ( 0 TL/s) oxygen consumption following a two hour • salinity change from 20 to 40 ppt standar­ dized for a 10 g fish. Dashed line is cal­ culated standard metabolic rate. (b) Time course of •metabolic scope for activity. • • 53 a 1400 • z g 1200 ;-, 10001 V1 '.C z~ SQQ Uo 47 soo I • z~ J ±­ • gg :~~1 J-r. ~ . A d 1 ~--------4----­ b • SQQ 600 • 400. zoa • -~i3o 1Z 2.4 30 4854 72. r1 ME (hours) • • Figure 11. Red drum 1S0 c, 20-10 ppt.--(a) Time course of· • active { 4 TL/s) , and .&. resting ( O TL/s) oxygen consumption following a one hour • salinity change from 20 to 10 ·ppt standar­ dized for a 10 g fish. Da~hed line is cal­ culated standard metabolic rate. (b) Time course of • metabolic scope for activity. • • • 14001 12001 • 1000 800 600 • 400 2.00 aoo • .60.0 • 2:00 ­ 1. a \ . I/~ f--r-1~· ~ b .. 7Z Tl ME (hours) • Figure 12. Red drum is0 c, 20-30· ppt.--(a) Time course of •active (4 TL/s), and A. resting (O TL/s) oxygen consumption following a one hour salinity change from 20 to 30 ppt· standar­ dized for a 10 g fish. Dashed line is cal­ • culated standard metabolic rate. (b) Time course of • metabolic scope for activity. • • z 1400.. • -0 ~ I• a. 1200 2: ~~~ 1000,.. , z.: .. 0 IC) . 800 u~ ON 600­ zo W. ~ -~ r;; 400.. >­ • x 2.00.. ~ a - ' - i'\'h--r---1-I +-I I A. ~ ~L~___.____.~...,.---~­ 0 -­ • b . 800.,.. ,,_.. It_ . .=· 600... w~ a...ro· o~ 400 ' \ -~ • U. er .·­ C./l 0 ~. __._ • • -·.,,.,,,, E " -~ ..,. 2.QO' ----. • I I I I I -r JG. 12. 2430 72. r1 ME (h.ours) Figure 13. Red drum lS0 c, 20-40 ppt.--·(a) Time course of •active (4 TL/s), and A. resting (O TL/s) oxygen consumption following a two hour salinity change from 20· to 40 ppt standar­dized for a 10 g fish. Dashed line is cal­ • culated standard metabolic rate. (b) TL~e ' course of • ·_metabolic scope for activity. • • This brief stress period was followed by a rapid increase in • maximum active metabolic rate which peaked at 6 hours after the change at both temperatures. Following this peak, the active rate decreased and remained fairly stable during the • second day. After 54 hours, however, there is a rise to another peak. • Metabolism and 20-to-10 ppt Salinity Change • Time course plots of metabolism following a change from 20-to-10 ppt exhibit the more typical time course pattern with reaction stressed, recovery and stabilizing phases as described previously. There are minor differences between species and between tempera.tures (see Figs. 2, 5, 8 and 11.}. • Although the 28°C time courses appear to have a slower rate of decrease in the active oxygen consumption rate inunediately following the salinity decrease, this may be due to the effect • of body size rather than temperature. The fish used at 28°C • were generally larger than those at 15°C due to normal seasonal growth.. In most cases the rate of decrease was slower for the larger fish (see Discussion} • The degree of recovery, however, appears to be dependent I • upon salinity and temperature. For spotted seatrout, the degree of recovery is greater at 28°C than at 15°C. The red drum data also indicate greater recovery at 28°C. Metabolism and 20-to-30 ppt Salinity Change • The metabolic responses to this salinity change show striking differences between species and between temperatures . • • 57 Spotted seatrout at 28°C show a marked recovery to a higher • level of scope at 30 ppt than at 20 ppt. There is also a very high degree of variability in this time course. At 15°C the recovery response was very slow in this experiment, and • it is questionable whether or not metabolic rates have been stabilized by the 72-hour termination of the experiments. Comparison of the 72-hour level at 15°C with other data • available for this species points to a severe depression of metabolic rate in the present experiment. For red drum, the response to a 20-30 ppt change is quite • unique at both temperatures as mentioned previously. Interpretation of the time course plot may be aided by examining the time course of blood osmolality for a 20-30 ppt change in this species • • (See Fig. 14b, discussed later.) • Metabolism and 20-to-40 ppt Salinity Change The metabolic response to a 20-40 ppt change is almost • identical between spotted seatrout and red drum at 15°C (see Figures 7 and 13) • The overall level of active metabolism, however, is higher in spotted seatrout. At 28°C (Figure 10) red drum exhibited no recovery phase and suffered greater than 50% mortality after 30 hours. The sequence at 28°C for spotted • seatrout (Figure 4) is somewhat erratic. The active rate measurement at 12 hours is thought to be high due to one aberrantly high reading. Spotted seatrout juveniles are clearly • more tolerant of increased salinities at high temperatures than red drum. • Blood Osmolality · • Whole blood osmolality was measured in small (1-5 g) juvenile red drum at 15 and 28°C. There was no perceptible difference between the two temperatures, however, and the • data were pooled for each time interval and summarized in Table 11. The salinity changes to increased salinities both yielded osmolality data which exhibited bimodal frequency • distributions at some point during the time course, with the higher mean level about 100 mOsm/kg higher than the lower mean level. Although mortality was not well recorded, there was a• higher mortality rate coinciding with the timing of the higher blood osmolality values (see Figure 14a and b) • The bimodality could be the result of laboratory diuresis, individual differences,• or sexual differences. • Osmolality and 20-to-10 ppt Salinity Change The 20-10 ppt salinity change is characterized by a very gradual decrease in osmolality over the first 6 hours from 326.7 to a level of about 316 mOsm/kg, followed by a • gradual increase over the next six hours (Figure 14c) • The time course is generally quite horizontal indicating only very slight perturbation of blood osmolality caused by a 10 ppt • reduction in salinity. No bimodality of osmolality measurements was observed. The isosmotic point for juvenile red drum is approximately 10 ppt• • • Osmolality and 20-to-30 ppt Salinity Change The 20-30 ppt change (Figure 14b) resulted in a rapid • Table 11• Time course of blood osmolality. Red drum. • • Time Salinity from Change Change ppt ·h N 20-10 -1 27 1 13 3 13 • • 6 13 12 13 24 13 30 13 48 12 54 10 72 13 20-30 -1 27 . 1 6 3 7 5 9 12 8 24 5 24* 3 • 30 7 30* 2 48 7 48* 2 • • 54 9 72 9 20-40 -1 27 3 8 6 12 12 16 24 13 30 7 30* 2 48 7 54 6 • 72 7 *Indicates observed bimodal are of the higher mode • Average Blood Osmolalitl mOsm•kg­ 326.7 320.6 318.7 315.8 322.1 315.9 317.8 320.8 315.3 322.5 326.7 344.0 354.3 349.2 340.1 327.0 380.0 332.8 419.5 329.6 407.5 350.0 359. 0 326'. 7 349.4 363.0 396.7 400.0 352.4 450.0 348.6 359.5 358.1 Standard deviation 9.5 11.2 8.5 5.9 12.2 6.2 12.1 8.3 13.l 5.0 9.5 26.5 22.4 23.2 15.9 10.9 16.0 9.3 14.8 26.5 3.5 24.9 31.9 9.5 10.5 13.0 36.4 47.0 7.6 42.4 15.2 8.3 17.9 frequency distribution. Values • • • • I • ") . • I Figure 14. Time courses of blood osmolali.ty for juvenile red drum following changes from (a) 20 to 40 ppt, I (b) 20 to 30 ppt, and (c) 20 to 10 ppt. 15°C and 28°C data are pooled. • • ' • • • • • • • l. ­ • • • • 61 20 40°/oo a460 420 380 yf /1 I I 340 i­ >-300 ·f-20 30°/oo b _J <( 420 l ..J.-l:f, O 'o· . ..:t:.. ~· 380. . ti) E: OQ-I E 340. 0 ·. Hi---I-· .0 -1a 300 20 10-a1oo, Cl. c 420 380 i: 340 I--! f-1 300 . -113 6 12 2430 4854 72 TI ME (hours) • increase in blood osmolality over the first 3 hours to a level • of 355 mOsm/kg. This was followed by a gradual decrease over . the rest of the first day. At 24 hours after the change, a bimodal frequency distribution of osmolality values appeared • which was not attributable to temperature, size, or any known variable. This phenomenon was also apparent at 30 and 48 hours after the change. There were single elevated points at 54 and • • 72 hours after the change, but the bimodal frequency constraint was not met and these points were lumped with the lower values. Interestingly, between 48 and 72 hours, average blood osmolality increased to the high level observed at 3 hours. Mortality was greatest during the second day of the time course • • Osmolality and. 20-to-40 ppt Salinity Change The salinity change from 20 to 40 ppt, over a two-hour period, caused a rapid increase in blood osmolality over the • first 12 hours to a level of about 4.00 mOsm/kg, which was maintained over the next 12 hours (Figure 14a) • At the 30­hour time frame, the mean level was down to about 350 mOsm/kg for • 7 out of 9 fish. Two fish had inordinately high values, which met the bimodal frequency constraint, and were given a separate mean and standard deviation. Several fish had elevated values of• blood osmolality at 12 and 24 hours after the change, but because of lack of· separate modes, these were lumped with the lower values, which resulted in wider standard deviations for these times • • Blood osmolality remained steady at around 350 mOsm/kg between 30 and 72 hours. This level is 25 mOsm/kg higher than the • • • • • • • • • • • acclimated 20 ppt level of 326.7 mOsm/kg. Mortality following this salinity change was greater than in the 20-30 ppt change and was highest during the first day • • DISCUSSION • General Emphasis is on relatively rapid adjustments to salinity change and on methods for assessing the accompanying metabolic • changes. Therefore this study is relevant indirectly to the usually very slow, natural changes in salinity regimes that occur in Texas coastal estuaries, especially in the case of • • increasing salinities. Sudden freshening of coastal waters, however, can occur within a day or so following torrential tropical storm-borne rains• • The effects of rapid changes in the osmotic, ionic, and solubility characteristics of the external medium are numerous. In fish, the most obvious and perhaps the most immediately • stressful variable is the osmotic pressure exerted upon the epithelial membranes of the gills. Reductions in salinity will cause water to enter the blood by osmosis unless the permeability • of the gill epithelia to water is reduced. The permeability of the gill to water is largely· controlled by endocrines, notably prolactin (Bern, 1975) , and levels of this hormone have been • shown to increase in Platichthys stel.latus upon transfers from seawater to freshwater (Johnson, et al., 1974). Outflux rates of individual ions, which are controlled by active transport and exchange processes usually involving ATP expenditure, are expected to and have been shown to slow after seawater to • freshwater transfers (Motais, et al., 1966; Bern, 1975; Maetz, 1974) • • • • Increases in salinity, on the other hand, would cause excessive water loss and dehydration if mechanisms of water • uptake and salt excretion were not well developed in the juvenile fishes involved in this study. Adaptation to increased salinity in teleosts involves an increase in drinking rate coupled • with increased salt excretion rates, especially at the gills (Motais, et al., 1966; Kirsch, 1972; Maetz, 1974). Changes in salinity involve costs to the organism for • regulation of transport and metabolic functions, which can change with an altered external environment. The magnitude of these costs on a steady state basis has been studied in fishes previously. The cost of osmoregulation usually increases with the osmotic gradient as salinity increases above the isosmotic • point (Rao, 1968; Fry, 1971; Nordlie and Leffler, 1975). However, - this should not be taken to mean that the optimal salinity for a species is at its isosmotic point. The metabolic responses to • salinity appear to involve more. than the cost of osmoregulation alone. Although the standard oxygen consumption rate may be lowest at the isosmotic point, the maximum capacity for activity • and the oxygen consumption rate at maximum activity has been shown to occur at salinities higher than the isosmotic. point in both species involved in this study (Wakeman and Wohlschlag, 1978;• Ilg, 1979). This suggests .that the "optimum" salinity may increase with increasing levels of activity for a salinity range of 10 to 30 ppt• • It should be noted here that metabolic scope is a measure of the oxygen consumption capability or capacity which may be used to pay the costs of stress from environmental circumstances. That • • • • • • • • • • • I i point where scope is highest along a gradient of some environmental variable may be considered an optimum in terms of the ability to use oxygen and perform at high levels of activity. This optimum, however, does not necessarily imply that other processes such as assimilation, growth, or reproduction are optimized at that point, although Brett's (1976) summary indicates that thermal optima are nearly identical for many processes • Another factor which has direct bearing on the above discussion is the effect of body size on the response to acute salinity changes and on the levels of oxygen consumption observed at acclimated conditions of differing salinities. The fundamental basis for the effect of body size is the increased surface/volume ratio of small fish relative to large ones. Small fish have proportionately larger· gill surf.ace areas and smaller blood volumes than larger fish, but this · fact alone does not directly answer the question of whether small or large fish are stressed more by salinity changes. ·While the small fish has more relative area which osmotic processes can act upon, they also have a larger regulating surface since the gills are the primary site of ionic regulation. The weight coefficients (bw) in the multiple regressions on oxygen consumption in Tables 1 and 2 show a decreasing trend with increased salinity. This would point to a higher relative oxygen consumption for small fish than large fish at high salinities. ·rt appears then, that the larger gill surface area of small fish is less beneficial because of increased osmotic pressure ·than. more beneficial because of increased regulatory area. • In order to determine the time course of adaptation to • salinity changes of varying degrees and directions, the metabolic data were subjected to a standardization procedure which related the data to a 10 g fish. Since the metabolic rate is largely • governed by body size, this procedure was necessary to make the various experiments, which utilized different sizes, directly --1 comparable. Velocity, already standardized by length, (TL s ), • also required further standardization because the active metabolic rate, which is measured at' observed maximum velocity, varied within experiments • • The observed maximum sustained velocity is here defined as the highest velocity at which the tail beat of the fish has a regular frequency and above which the fish changes to a burst • and glide mode of swimming. This definition works well for single, large fish, but when over 30 juveniles are in the chamber, a certain amount of subjectivity is induced. Because of this • problem, all active data were. standardized for a 10 g fish swimming at 4 TL s-l using multiple regressions from Tables 1 and 2. The only basic problem with this procedure is that it ignores • the probable interaction of the variables of weight and velocity. Fortunately, only relatively small weight and activity ranges are involved in these standardizing procedures for 10 g and 1 • 4 TL s-, but for larger size and activity ranges a separate study of weight and velocity interactions would be required. The resting oxygen consumption rate at 28°C is elevated far • above the estimate of standard metabolism for this temperature, which is probably due to spontaneous and uncontrolled physical • • 68 activity by the fish at this temperature. Field collected red • drum during the summer were too large to use in the flasks, so usually smaller juveniles which were obtained from the Texas Parks and Wildlife Department were used for resting measurements. · • Since measurements of the resting rate took place in sealed 2.9 1 flasks, the smaller the· fish, the less restrictions on its movement. The fact that 28°C is far above the temperatures • normally experienced in winter and spring by small juveniles may be an important factor as well! Uncontrolled and unmeasured activity is a major drawback for the use of the "resting" metabolic rate as an indicator for any purpose. For this reason, calculations of metabolic scope utilized the estimate of the standard metabolic rate from the • regressions in Tables 1 and .2, rather than measured values of the "resting" metabolic rate. This procedure assumes that the standard rate is constant after the salinity change. While • this assumption is not absolutely true, changes in the standard rate are usually very small relative to those in the active rate, so that the estimate of scope is only slightly affected • by the assumption. The observed, small changes in the resting rate tend to support this procedure. Since variations in the active metabolic rate are much greater than those observed in • oxygen consumption at low levels of activity, the magnitude metabolic scope is much more arithmetically dependent on the • active metabolic rate. Because of this direct correlation, the analyses on the time courses which follow deal directly with the active metabolic rate, although it should be noted that • the same relationships generally hold for metabolic scope• • Metabolic Responses • The general shape of the time course of metabolic responses was described in the results section. For purposes of discussion, the various phases of an idealized time course are labeled in • Figure 15. The majority of the time courses in Figures 2-13 seem to lend themselves to this division. The observed decrease in the active metabolic rate following the salinity change is, • in itself, interesting in view of the fact that performance (velocity) did not· decrease proportionately as would be expected (see Tables 7-10). The efficiency of swimming superficially • appears to increase during this period, which is highly questionable and indeed unlikely. A second explanation could involve a large increase in the anaerobic component of metabolism• • A sustained anaerobic component of· this magnitude, howeve-r, must be viewed with a great deal of skepticism, because the muscle fibers involved in glycolysis are not adapted for swimming activity • on a sustained basis (Goldspink, 1977; Bilinski, 1974). Perhaps the best explanation, therefore, involves the possibility of a reduced energy allocation to such energy demanding processes as • anabolic metabolism. A temporary reduction in the processes of growth and synthesis may be the price paid.for the costs of adaptation to salinity changes when activity, growth, and ion­osmoregulation compete for energy. \ • The direction or degree of salinity changes has surprisingly little effect on the rate of .short term metabolic adaptation. In the majority of cases, a large degree of recovery and possible stabilization has occurred by 30 hours. Since the level of • • 70 • • : QJ ~­ er Cl: r-eac:tiorr recovery ~ ~h~ pnas& • >· ....... staailizing u \ < /stressed ~ase phase-C­ ' I a QJ 0 t.. u~ ...en ~ • ._'­ -5 0 o. ~ c 0. .2. ..... ..... a 0­ • t-.. -· ·-..... ::r a. c: • 10 20 30 40 Fl NAL SALlN I TY ( t:iPt) • Fiqu:re L7. Eistoqram showinq the relationship of '5S$S$1• the duration of t..~e stressed phase, and • .___.r the time of initiation of the recovery phase to salinity L~ juvenile red. drum• • for 20-30 ppt changes in red drum. Spotted seatrout showed no • such discernable trends • The time of initiation of the recovery phase shows a very weak positive correlation with body size over the small (< 25 g) size range. Again, salinity appears to be the primary factor governing· the rapidity of recovery, at least in red drum (see Figure 17). The weak correlation with size suggests, however, • that small juveniles may be more resilient to sublethal salinity stress even though increased salinity affects them more, due to surface-volume considerations• • The level of the stabilization. phase is clearly a function of salinity as shown in Figure 18. While the data here are probably insuff1cient to predict the salinity optima, the basic shape and position of these relationships agree with previous data (Wohlschlag, 1977). The depressed value of the active metabolic rate of the spotted seatrout at 15°C, 30 ppt, is • probably a result of· stress from trawl capture as discussed below. Since by definition a fasted condition is necessary for the metabolic determinations in this experiment, an effect of • starvation may cause a slight reduction in the level of stabilization by the end of 3 days. For this reason, the level of stabilization as depicted in Figure 18 should not be over­ • emphasized. In relation to salinity changes, the effect of temperature was most apparent in juvenile red drum in changes from 20 to 40 • ppt. The fish showed a typical response and recovered at 15°C but suffered mortality and did not recover at 28°C. The mortality • • • • • Figure 18. Active metabolic rates at 72 hours after the salinity change versus • final salinity at • 28°C and o 15°C, for spotted seatrout and red drum. • • • • • • • • • • • • • • • • Spott E: 600 w r­ < 400 a: -u ~-200 0en. < t-b· W, Rczddrum ~ 1000 w < > I-800 u < 600 400 200 10 20 30 40 SALINITY (ppt) • 77 may have been associated with the fact that 28°C is fairly close • to the upper lethal temperature for red drum (approx. 32°C) • Fish show different responses to the upper lethal temperature than to the lower, death being more abrupt at high temperature • and less so at low temperature. (Fry, 1957). Another factor which is almost certainly important in this case is that one of the experiments involved unseasonably small (1-2 g) juveniles • obtained from the Texas Parks and Wildlife Department. Juveniles of this size are probably seldom exposed to high salinities at temperatures as high as 28°C, because they reach this size in • the winter months and by summer are considerably larger. Yokel (1966) reported a direct relationship between size and salinity for this species: he noted that small fish are more common at • low salinity and large fish are more abundant at higher salinities. Spotted seatrout juveniles appear to be more tolerant of increased salinities at 28°C. The optimal spawning temperature • for this species is 28°C (Taniguchi, in press; Weaver and Perret, 1979), so the high temperature is not expected to be a stressing factor for these juveniles• • In spotted seatrout~ at 28°C (Fig. 3), the change from 20 to 30 ppt resulted in a higher stabilized active metabolic rate at 30 ppt than at 2:10 ppt. At 15°C, however, the recovery phase was very gradual and resulted in a lower active rate at 30 ppt than at 20 ppt. The only difference noted in the 15°C experiment is that the fish were captured by otter trawl. This method of • capture causes more damage to skin and scales. The observed response to salinity changes from 20 to 30 ppt in red drum (Figs. 9, 12) deserves mention. The pattern observed • • • at both temperatures differs markedly from the pattern observed at all other salinity changes and from that of the spotted • seatrout. The fact that the change is toward the optimum salinity probably has some pertinence. If the fish's physiology is regulated such that it is capabl.e of greater oxygen consumption • at 30 ppt, it is not implausible that an overshoot and subsequent compensation could account for the first peak at 6 hours. As for the second peak, blood osmolality· (Fig. 14) is observed to begin a second increase at 48 hours. ·This could eli9it a metabolic response, but one would expect it to be a negative one rather • than the observed peak ·in the active metabolic rate at 54 hours • For the present, random variability or some type of behavioral manifestation is perhaps· the best explanation• • Blood Osmolality The observed changes in blood osmolality (Fig. 14) following the experimental salinity changes for red drum show a general correlation with the metabolic responses. By 30 hours, a degree of stabil.i ty is observed in all three cases. The perturbations • in osmolality agree .both in direction and degree with changes in the external salt concentration. The elevated values observed following salinity increases are possibly the result of laboratory • diuresis (Kinne, 1962}. Since the salinity history of the fishes is unknown, however, these may represent a case of irreversible nongenetic adaptation (Kinne, 1.962). If the juveniles in question • were spawned at low salinity, their adaptational response to increased salinity may be impaired• • • 79 The 72-hour level of blood osmolality is considerably higher • at both 30 and 40 ppt than at 20 ppt. This observation was also • noted in a separate experiment where juvenile redfish were allowed to adapt for 14 days. The implications of this difference are that every cell in the organism must adjust to a new internal milieu• This could be the bas.is .for the observed salinity optima between 20 and 30 ppt for red drum. • The fact that.temperature had no apparent effect on blood osmolality is contrary to that observed for Fundulus heteroclitus (Umrninger, 1968). This species showed higher concentrations of • Na+ and Cl-in winter than in summer. Prosser, et al. (1970) suggest that this could have energy saving properties by reducing the osmotic gradient when energy supply is low in the winter • • There are actually too few data points to determine statistically - the effect of tempera:ture on blood. osmolality in this experiment, so this question should not be considered answered. At 30 ppt, blood osmolality {Fig·. 14) shows a second increasing trend beginning two days after the salinity change. Associated increases in the standard deviation of the means are also apparent. • The physiological basis for this increase is unknown, but starvati.on, periodicity, a. real pattern of regulation, or random variability are all possible explanations • • The very slight perturbation of blood osmolality in 20-10 ppt changes is interesting in that it suggests that these small juveniles adapt to rapid salinity decreases faster than to salinity • increases. In view of the fact that rapid salinity decreases in the estuaries due to heavy rainfall and rapid runoff are much • • more common than rapid increases due to evaporation, this • result is expected. Potts (1954), on theoretical grounds, has shown that the energy expenditure involved in regulation to dilution of the medium is less demanding than regulating • for increased concentration• • • • • • ·• • • • CONCLUSIONS • 1. Initial metabolic responses of juvenile (less than 25 g) spotted seatrout and red drum, which had been acclimated to an optimal salinity of 20 ppt and then subjected to a reduction • to 10 ppt or increases to· 30 or 40 ppt, were: a. The active metabolic rate was reduced substantially. b. The scope for activity was reduced substantially. • c. The standard metabolic rate changed relatively only slightly. 2. Following the salinity increase or decrease the active rate • and scope decreases briefly during a "reaction" phase. • 3. The initial active metabolic rate decrease is either followed by an immediate gradual increase in the active rate in a "recovery" phase or followed by a continued relatively low metabolic state termed a "stressed" phase. The stressed phase was always present for salinity changes from 20 to 10, and from 20 to 40, ppt and was followed either by death or a recovery phase • • . 4. Changes from 20 to 30 ppt were not necessarily stressful• 5. Following the recovery phase, the active metabolic rate tends to level off in a "stabilizing" phase. • 6. The stabilizing phase is usually at a lower level for both • active metabolism. and for scope than the initial levels at 20 ppt, except for the changes to 30 pp-E. US:\lcitlJ₯ the stabilizing phase began about 30 hours after the salinity change . 7. Smaller juveniles show a faster rate of decrease in active metabolic rates during the reaction phase and an earlier recovery • • phase. The explanation is suggested by the relative changes in • the gill surface-to-volume ratios with growth . 8. Since a large degree of metabolic stabilization has occurred by 30 hours after salinity changes from an acclimated 20 ppt to • 10, 30, or 40 ppt, it is conservatively estimated that short term salinity acclimatization occurs in about 48 hours, except for a few deaths • • 9. The duration of ·the stressed phase for red drum is apparently related directly to the amount of salinity increase above 20 ppt, while a decrease to 10 ppt had a stressed phase of intermediate • duration. 10. The time from the salinity change to the beginning of the recovery phase was generall.y shorter for the smaller of the red• drum juveniles. 11. The level of stabilization in the active metabolic rate or in the scope level was a direct function of salinity, both with • optima between 20 and 30 ppt, as indicated for larger specimens in earlier studies. 12. Except where temperatures· are comparatively high, the effect • of temperature on the salinity acc·limation processes is apparently not great. Normal seasonal times of hatching, growth, and temperatures. should be taken into consideration concomitantly in • salinity change evaluations. 13. The observed changes in blood osmolality following salinity changes tend to follow both the degree of salinity change and • the changes in metabolic responses. However, a fair proportion of individuals seemed unable to regulate for salinity increases • • • • • • • • • • • • to 30 and 40 ppt and suffered mortality. This inability to regulate could be explained by laboratory diuresis or by too rapid exposure to too great a salinity change. 14. The general application of small fish to evaluate rapid changes from ideal estuarine salinity conditions to salinities that may be less than optimal seems to be a worthwhi.le analytical approach for future fishery resource assessments. The general subtleties observed in this-study should be used as a basis of precautions in future applications, however • • ACKNOWLEDGMENTS • As pointed out in the introductory note, this report is almost entirely based on the M.A. thesis of Michael P. Gunter, to whom sincere thanks are extended. Ronald J. Ilg, in • conjunction with his dissertation research on small fish helped in virtually all phases of this project in field, laboratory, and data processing operations. Special acknowledgment is • accorded Edgar Findley, Neal Smatresk, Tad Crocker, among others, who helped with various phases. Special thanks are extended to • Captain Elgie Wingfield of the R/V LORENE, and to Noe Cantu and Hayden Abel of the R/V BEVO. The efforts of the Texas Parks and • Wildlife Department are especially appreciated for providing juvenile red drum for some o·f the experiments • • This study was performed under Interagency Cooperation Contract No. IAC (78-79)-·1840, under the aegis of Texas Department of Water Resources, Contract No. 14-90019. We are particularly • grateful for encouragement and advice of Gary L. Powell of TDWR throughout. We appreciate the help of Geraldine Ard, Helen Garrett and Patti Gunter with the typing chores • • • • LITERATURE CITED • Bern, H. A. 1975. Prolactin and Osmoregulation. Amer. Zool. • 15:937-949. Bilinski, E. 1974. Biochemical aspects of fish swimming. • p. 239-288. In: D. c. Malins and J. R. Sargent (eds.), Biochemical and Biophysical Perspectives in Marine Biology, Academic Press, New York • • Brett, J. R. 1964. The respiratory metabolism and swimming performance of young sockeye salmon. J. Fish. Res. Bd. Canada. 21:1183-1226 • • • 1976. 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