Shrimp and redfish studies: Bryan Mound brine disposal site off Freeport, Texas, 1979-1981. Volume VI. Brine toxicity and avoidance/attraction bioassays on shrimp.

Salt brines mixed from salt dome salt (Ranch House Coarse Salt, United Salt Co.) or Instant Ocean (Aquarium Systems, Inc.) and Brazos River water or deionized water were tested for toxicity and for behavioral and physiological effects on large white shrimp (Penaeus setiferus) and large brown shrimp (Penaeus aztecus). Results indicate that half of a group of animals at 25 C can be expected to die 48 hr after an addition of enough brine to raise salinity by 22 o/oo or after 96 hr when salinity is increased by 18 o/oo. Sensitivity to brine was greater at 30 C in both species, and white shrimp survived brine better as temperature was lowered to 15 C. Animal size did not affect brine survival, nor were there consistent differences in the effects of different brine types. The latter finding suggests that the principal lethal effect of brine is osmotic stress rather than toxicity of trace constituents. The relationship between mean time to death and salinity increase indicates that large animals of either species can be expected to surive well over 500 hr at the worst-case salinity predictions (6.5 o/oo above ambient) for the diffuser site. Heart rate and animal color were significant signs of incipient brine stress. Behavior experiments were conducted by exposing animals to brine plumes in still water or by offering animals a choice between brine-sea water mixtures and sea water. Results showed an increase in activity for animals that were subjected to brine-sea water mixtures 10 o/oo or more above their previous environmental salinities. In choice experiments, animals were somewhat repelled from toxic brine concentrations (20 o/oo) but not from lower tested concentrations. Neither behavioral effect is likely under field conditions where worst-case salinity increases are expected to be much lower than 10 o/oo.