Influence of osmotic stress on upper lethal temperatures in the cyprinodontid fish Fundulus heteroclitus (L.)

Abstract

Upper lethal temperatures determined for the mummichog Fundulus heteroclitus (L.) for exposures of 10 000 min ranged from 18.58C to 36.31C. Osmotic acclimations were prepared at 0, 14, and 32‰ salinity (S), at thermal acclimations of 5 and 15C, and at 14 and 32‰ S at 25C. Mummichog could not survive in the acclimatory combination of 0‰ S at 25C. Subsamples from these acclimatory combinations were exposed to thermal stress at 0, 14, and 32‰ S. Highest upper lethal temperatures were observed in isosmotic test salinity (14‰). Intermediate lethal levels occurred in seawater (32‰ S) and the lowest lethal temperatures occurred in fresh water (0‰ S). Upper lethal temperature increased with increasing thermal acclimation but generally, prior osmotic experience did not modify thermal tolerance. There was no relation between order of death and size in 18 of the 24 test combinations. In the remaining six, the largest members died first in four and the smallest died first in two test combinations.