Dietary effects of metals-contaminated invertebrates from the Coeur d'Alene River, Idaho, on cutthroat trout

Benthic macroinvertebrates with elevated concentrations of metals were coll ected from the Coeur d'Alene (CDA) River, Idaho, pasteurized, and fed to cu tthroat trout Oncorhynchus clarki in the laboratory from start of feeding u ntil 90 d posthatch. Invertebrates were collected from two sites known to c ontain elevated concentrations of metals: near Pinehurst in the South Fork of the CDA River and at Cataldo, approximately 5 km below the confluence of the South Fork and the North Fork. Invertebrates collected from a relative ly clean site in the North Fork were used as a reference diet. We performed measurements of fish health that indicate reduced fitness of fish fed the South Fork and Cataldo diets. Effects measured were reduced feeding activit y, increased number of macrophage aggregates and hyperplasia of cells in th e kidney, degeneration of mucosal epithelium in the pyloric caecae, and met allothionein induction. These effects would likely reduce growth and surviv al of fish in the wild. Vacuolization of glial cells were also observed in fish fed the Cataldo diet. Metals in the water often exacerbated the histol ogical effects observed. Although the invertebrates collected near Cataldo had lower concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead ( Pb), and zinc (Zn) than the invertebrates from the South Fork, fish fed the Cataldo diet had equally high or higher concentrations of all metals excep t As by day 44. The Cataldo diet also caused the most deleterious effects o n survival and growth. These findings are especially important for early li fe stage fish, whose diet consists wholly of benthic macroinvertebrates. Th erefore, fish feeding on invertebrates in the CDA River below the Bunker Hi ll smelting complex are at risk of reduced fitness.