Size-specific mortality in fry of lake trout (Salvelinus namaycush) from Lake Michigan.

Abstract

A study to test the presence and magnitude of size-specific mortality in fry from Lake Michigan lake trout and fry of hatchery origin during exposure to PCBs is presented. Fry from both sources were exposed to 50 ng/l PCBs for about 50 days after hatching and fry from both sources were reared in water to which no PCBs were added. The average lengths of fry from all four groups were significantly less than fry from Lake Michigan. Size-specific mortality observed in fry of Lake Michigan origin could be the result of a number of factors, including origin and condition of parents and environmental stresses, including organic contaminants. Higher mortality of the smaller fry might be considered to have a positive effect on long-term fish production in the larger fish are being selected for, however, decreasing genetic variability in the fish population can result in lower production. Considering the similarity between the physiochemical properties of PCBs and DDT, the substantial concentrations of PCBs in the fry of lake origin may be an important factor in explaining the size-specific mortality observed.