Survival of Red Drum Fingerlings In Fresh Water: Dissolved Solids And Thermal Minima

Laboratory bioassays were conducted to estimate lower dissolved solids and temperature thresholds of red drum (Sciaenops ocellatus) fingerlings. Tolerance to low total dissolved solids (TDS) was measured by subjecting fingerlings to various test concentrations for 240 hours at 21° ± 1°C. Higher mortality in fresh water than in diluted sea water with similar TDS suggested that concentration of individual ions may be more important than TDS to survival of red drum in fresh water. Survival in solutions of increasing sodium chloride concentrations, but constant TDS, increased and was greater than 80% at chloride levels above 130 mg/liter. Tolerance to low temperature was measured by exposing fingerlings to different temperature regimes in fresh water adjusted to a concentration of 150 ± 5 mg/liter chloride. Lower lethal temperatures ranged from 3.0° to 0.8° C when water temperature was reduced 1° C per day. When temperature was reduced 1° C every 3 days and maintained at 4° C, time to death was between 48 and 168 hours. Regardless of rate of temperature decrease, feeding ceased between 9° and 5° C. Stocking of red drum fingerlings should be successful in fresh waters that have chloride concentrations exceeding 130 mg/ liter and temperature above 9° C.

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