Lethal and Preferred Temperatures of the Alewife (Alosa pseudoharengus) in Lake Michigan

Abstract

The temperature tolerance and temperature preference of mature and young-of-year alewives from Lake Michigan were studied in the laboratory. Critical thermal maxima and incipient upper lethal temperatures increase with acclimation temperature for both mature and young-of-year fish. Critical thermal maxima at equivalent acclimation temperatures are unaffected by age of the fish. Incipient upper lethal limits for young-of-year fish exceed those for mature fish by 3 C to 6 C. The ultimate lower lethal temperature for mature alewives appears to exceed 3 C. Loss of heat tolerance following a 10 C decrease in temperature occurs at approximately one-half the rate of gain of heat tolerance following a comparable temperature increase. Preferred temperatures for young-of-year alewives were consistently higher than those of mature fish. Seasonal factors other than lake temperature appear to be of considerable importance in determining preferred temperatures. The results are discussed in terms of potential effects of the heated plume from a nuclear generating station and available field data.