Resistance of Texas salt- and freshwater-marsh fishes to heat death at various salinities.

Response-surface diagrams were used to compare the resistance of ten species of marsh fishes to heat death at various salinities. As a group the marsh cyprinodonts are the most resistant fishes known and Cyprinodon variegatus appears to be the most resistant to heat death of the fishes tested in laboratory experiments. The habitat of a species within the salt marsh correlated with its relative resistance to heat death. Some dissolved solids in the water benefited all species during exposure to high temperature. As temperature decreased optimum salinities for survival decreased for freshwater fishes and increased for salt marsh fishes. A sample of salt marsh Gambusia affinis was found to be more resistant to heat death at salinities of 10 and 20 ppt than was a sample from freshwater.