Effects of Heavy Metals on Prey Abundance, Feeding Habits, and Metal Uptake of Brown Trout in the Arkansas River, Colorado

Abstract

We examined the effects of heavy metals on prey abundance, feeding habits, and metal bioaccumulation of brown trout (Salmo trutta) at two sites in the Arkansas River, a Colorado stream polluted by mining discharges. We hypothesized that altered prey communities and exposure to metals would affect brown trout feeding habits, bioaccumulation, and condition. Prey communities at the upstream reference station (AR1) were dominated by metal-sensitive mayflies (Ephemeroptera) and black flies (Diptera: Simuliidae), whereas those at the downstream polluted station (AR5) were dominated by metal-tolerant chironomids (Diptera: Chironomidae) and caddisfiies (Trichoptera). Differences in prey community composition were reflected in the feeding habits of brown trout, which consumed greater numbers of chironomids and caddisflies at station AR5. Concentrations of heavy metals (Cd, Cu, and Zn) in water, dominant prey taxa, and brown trout stomach contents were greater at station AR5. Metal levels were also significantly elevated in brown trout gill and gut tissue at the downstream station, indicating greater metal exposure. However, in contrast to our predictions, metal levels in liver and kidney tissue, the primary organs of metal storage and regulation, were either similar at stations AR1 and AR5 or greater at the upstream station. In addition, brown trout size and condition factors (weight/length3) were significantly reduced at station AR1 compared with AR5. Condition factors were significantly correlated with metal levels in liver tissue at AR1 but not at AR5. We hypothesize that greater prey abundance and slightly warmer water temperature at the downstream station influenced fish condition and metal regulation in brown trout. These results demonstrate that bioaccumulation of metals by brown trout in the field is complex and influenced by several factors in addition to metal levels in food and water.