METALS-CONTAMINATED BENTHIC INVERTEBRATES IN THE CLARK-FORK RIVER, MONTANA - EFFECTS ON AGE-0 BROWN TROUT AND RAINBOW-TROUT

Benthic organisms in the upper Clark Fork River have recently been imp licated as a dietary source of metals that may be a chronic problem fo r young-of-the-year rainbow trout (Oncorhynchus mykiss). In this prese nt study, early life stage brown trout (Salmo trutta) and rainbow trou t were exposed for 88 d to simulated Clark Fork River water and a diet of benthic invertebrates collected from the river. These exposures re sulted in reduced growth and elevated levels of metals in the whole bo dy of both species. Concentrations of As, Cd, Cu, and Pb increased in whole brown trout; in rainbow trout, As and Cd increased in whole fish , and As also increased in liver. Brown trout on the metals-contaminat ed diets exhibited constipation,,out impaction, increased cell membran e damage (lipid peroxidation), decreased digestive enzyme production ( zymogen), and a sloughing of intestinal mucosal epithelial cells. Rain bow trout fed the contaminated diets exhibited constipation and reduce d feeding activity. We believe that the reduced standing crop of trout in the Clark Fork River results partly from chronic effects of metals contamination in benthic invertebrates that are important as food for young-of-the-year fish.