Thermal preferences of mummichog, Fundulus heteroclitus L., and banded killifish, F. diaphanus (LeSueur), (Cyprinodontidae) in relation to thermal acclimation and salinity

Frequency distributions corresponding to various levels of thermal acclimation from 5 to 35 °C were recorded for samples of marine mummichog, Fundulus heteroclitus L., and samples of freshwater banded killifish, F. diaphanus (LeSueur), in thermal gradients formed in columns of fresh water (< 0.5‰ salinity) or sea water (32‰ salinity). Mean preferred temperatures comprised roughly parallel but irregularly inflected trends for the two series of tests, within each species. In mummichog, preferred temperatures for corresponding thermal acclimations ranged from 3 to 6 °C higher in tests conducted in sea water. In banded killifish, preferred temperatures for corresponding thermal acclimations ranged from 5 to 8 °C higher in fresh water. Thus, each species regularly preferred higher temperatures in salinity which approximated that of the typical habitat. The inference to be taken is that the unusual salinity for each species places an extraordinary osmoregulative load which influences the reactions of the fish to the series of thermal or other correlated stimuli in the gradient.