Shrimp and redfish studies; Bryan Mound brine disposal site off Freeport, Texas, 1979-1981. Volume V(A): Brine toxicity bioassays on redfish.
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Redfish or red drum, Sciaenops ocellata (Linneaus), embryos, larvae, and juveniles were exposed to four test brine solutions: artificial sea salts in distilled water, dome salt in Brazos River water, dome salt in distilled water and artificial sea salt in Brazos River water, at various combinations of temperature and salinity. Embryos were exposed for 72 h, and larvae for 120h, to four brine types, four salinities (34, 36, 38, and 40 ppt.) and three temperatures (23, 26, and 30 C), resulting in a 4x4x3 factorial design. Juveniles were exposed for up to two weeks in acute concentrations of dome salt/Brazos river water brine. Embryos were the most sensitive life stage and juvenile redfish the most resistant to brine concentrations. Response surface methodology indicated that in general, salinity effects were more dominant than temperature effects. Salinities above 38 ppt adversely affected embryonic survival in all brine types, whereas temperature had no consistant effect upon embryonic survival. Brine prepared with dome salt and Brazos River water represented the most toxic exposure condition for redfish embryos. The optimal conditions for hatching success and embryonic survival of redfish were combinations of mid-range salinities (34-36.5 ppt) and temperatures (23-26C) in all brine types. Embryonic survival decreased markedly in all brine exposures after 72h exposure, presumably due to difficulty in the transition from endogenous to exogenous nourishment. Redfish larvae (2 weeks old) were more resistant to brine exposure than embryos and did not respond differentially to different brine types until after 96 h exposure when slightly greater survival occurred in artificial sea salt/Brazos River water brine relative to the other three brine types. Survival of juvenile redfish was affected by concentrations of dome salt/Brazos River water brine exceeding 5 ppt in seawater. The present investigation has indicated that dome salt is the most toxic element of the brines which were tested and that Brazos River water was more toxic to redfish in early life stages than distilled water. The most critical factor influencing early development of redfish appears to be successful transition from endogenous nutrition to exogenous feeding (i.e. 72-80 h). Redfish larvae which successfully make this transition would be expected to survive in low concentrations of brine in a field situation.