A critical review of the effects of contaminants on early life stage (ELS) mortality of lake trout in the Great Lakes

A review was none to assess whether epizootics of early life stage (ELS) mortality in Great Lakes lake trout (Salvelinus namaycush) that occurred during the late 1970s to the present, could have been related to the concentrations of major contaminants such as PCBs, DDT, PCDDs, and PCDFs measured in their eggs. Results of laboratory studies were used to establish mode of action, toxic effects, and minimum concentrations required to induce these effects by these chemicals. It appears unlikely that the more common causes of mortality, including reduced hatching, blue sac disease, and swim-up syndrome mortality in lake trout eggs were solely related to the contaminants measured in eggs and larvae. Laboratory studies suggest the concentrations required to induce increased hatching mortality and blue sac disease are much higher than levels measured in feral fish eggs. Swim-up syndrome has never been correlated with chemical exposure. Several alternate explanations relating to egg rearing conditions, nutrition, poor egg quality, and altered physiology are discussed. These factors may have interacted with the sublethal concentrations of contaminants to cause some of the observed mortality.