Effects of Hypolimnetic Discharge on Fish Health Below a Reservoir

Abstract

Rainbow trout (Salmo gairdneri), brown trout (Salmo trutta), brook trout (Salvelinus fontinalis), and yellow perch (Perca flavescens) from two locations in the Buford Dam, Georgia, tailwater and trout from a hatchery that used the tailwater as a water supply were examined for infections, lesions, and liver metal concentrations. Nine genera of parasites, 19 species of bacteria, and one species of virus infected the fish. River fish had no clinical signs of disease resulting from the pathogens. In the hatchery some deaths were caused by bacterial infections, but many moribund fish were not infected. Bacterial isolations from river fish were most frequent in fish collected near the dam and near the date of lowest dissolved oxygen (DO) concentration. Microscopic lesions were found in the gills, liver, spleen, and trunk kidney of many of the fish that did not have bacterial infections. Rainbow trout were most affected by the conditions in the tailwater and hatchery, and brook trout and yellow perch were least affected. Occurrence of lesions that indicated exposure to a toxicant corresponded to increases in iron and manganese concentrations of the water, but not to copper concentrations. Manganese levels in liver were high compared to published reports. Copper concentrations in liver varied with fish species, and those of brook trout were lower than published values for this species exposed to “no effect” copper levels. Liver concentrations of zinc and cadmium did not indicate exposure to high levels of these metals. Copper, zinc, iron, manganese, and DO concentrations of the tailwater in this study or previous reports were levels that indicated possible harmful effects to fish. Acclimation to the tailwater conditions may have allowed survival of fish in the river. Low pH, oxidation-reduction potential, and DO concentrations, and high metal concentrations resulted from release of hypolimnetic water from the impoundment. Most bioassay data are not reliable for prediction of toxicity in tailwaters because of the water characteristics, acclimation of fish, and possible synergistic actions.