Analysis of freshwater inflow effects on metabolic stresses of south Texas bay and estuarine fishes : continuation and extension : draft final report to Texas Water Development Board (Texas Department of Water Resources)




Wohlschlag, Donald E. (Donald Eugene), 1918-2007

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Continuation studies of freshwater influx effects were conducted on five common South Texas fish species in 1976-77. The studies were designed to determine the optimum salinities and the salinity ranges over which these five species could effectively exist. The procedures were designed to evaluate salinities over and above effects of pollution or depletion due to excessive exploitation. The rationale of the respiratory metabolism experiments was to measure the metabolic scope for each of the five species at salinities of 10, 20, 30 and 40 ppt. Scope is the difference between the maximum metabolic rate for fish swimming at maximum sustained speeds and the minimum metabolic rate (standard rate) for fish at complete rest. Respiratory metabolism is measured by the amount of oxygen consumed by a fish each hour. In addition, the maximum sustained swimming rates at each salinity could be plotted to determine the optimum salinity for the maximum overall swimming rate. Any stress, such as salinity too high or too low compared to the optimum salinity would depress the scope or the swimming speed. When the metabolic scope for active fish falls to about twice the level of the standard maintenance rate, a fish will be barely able to maintain its foraging and digestive requirements without growth and other metabolic requirements. At these upper and lower limits the overall salinity range of the species can be defined.
30 September 1977
For Interagency Cooperation Contract. IAC (76-77)-1690