Upper lethal temperatures of threespine stickleback, Gasterosteus aculeatus (L.), in relation to thermal and osmotic acclimation, ambient salinity, and size

Abstract

Samples of threespine sticklebacks, Gasterosteus aculeatus (L.), collected in seawater at Halifax, Nova Scotia, were acclimated to six combinations of conditions at 10 and 20C and in 0, 12, and 30‰ salinity (S). Bioassays of 10 000 min were performed at various constant temperatures from 20 to 30C in the diallel combinations of acclimation and salinities of 0, 12, and 30‰. Highest upper lethal temperatures, corresponding to combinations of acclimation, occurred in isosmotic test salinity of 12‰. Upper lethal temperatures ranged in all tests from 28.76 to 21.63C. A 10-degree increase in thermal acclimation resulted in increases in upper lethal temperature ranging from −0.27 to 0.77 degrees in tests conducted at 12‰ S and increases ranging variously from 1.45 to 3.56 degrees in tests conducted at 0 and 30‰ S. Upper lethal temperatures were shifted significantly by the ambient salinity but not by salinity of acclimation. Within the range of total lengths, 30–80 mm, there were no significant differences in mean lengths of dead and surviving fish in relation to acclimation temperatures and test salinities. There was no rank-correlation between order of death and total length in 15 of 18 test combinations.