EFFECTS ON RAINBOW-TROUT FRY OF A METALS-CONTAMINATED DIET OF BENTHICINVERTEBRATES FROM THE CLARK FORK RIVER, MONTANA

The upper Clark Fork River in northwestern Montana has received mining wastes from the Butte and Anaconda areas since 1880. These wastes hav e contaminated areas of the river bed and floodplain with tailings and heavy metal sludge, resulting in elevated concentration of metals in surface water, sediments, and biota. Rainbow trout Oncorhynchus mykiss were exposed immediately after hatching for 91 d to cadmium, copper, lead, and zinc in water at concentrations simulating those in Clark Fo rk River. From exogenous feeding (21 d posthatch) through 91 d, fry we re also fed benthic invertebrates from the Clark Fork River that conta ined elevated concentrations of arsenic, cadmium, copper, and lead. Ev aluations of different combinations of diet and water exposure indicat ed diet-borne metals were more important than water-borne metals-at th e concentrations we tested-in reducing survival and growth of rainbow trout. Whole-body metal concentrations (mu g/g, wet weight) at 91 d in fish fed Clark Fork invertebrates without exposure to Clark Fork wate r were arsenic, 1.4; cadmium, 0.16; and copper, 6.7. These were simila r to concentrations found in Clark Fork River fishes. Livers from fish on the high-metals diets exhibited degenerative changes and generally lacked glycogen vacuolation. Indigenous Clark Fork River invertebrate s provide a concentrated source of metals for accumulation into young fishes, and probably were the cause of decreased survival and growth o f age-0 rainbow trout in our laboratory exposures.