Sublethal Copper Effects on Bluegill, Lepomis macrochirus, Foraging Behavior

Abstract

The effects of four copper concentrations (5 [control], 31, 180, 1710 μg L−1) on bluegill (Lepomis macrochirus) foraging behavior were examined with two separate experiments; one experiment assessing copper effects on the reaction distance of bluegill to two sizes of untreated zooplankton and one assessing copper effects on the functional response of bluegill to untreated (five tests) and treated (five tests) invertebrate prey. Prey used in these experiments were: Daphnia pulex, D. magna (Cladocera), Hyalella azteca (Amphipoda), and two sizes of Enallagma sp. (Zygoptera). Copper had no effect on the reaction distance of fish to zooplankton. There was a significant negative dose-response relationship for consumption rates of all untreated prey but not of treated prey groups. Prey handling time for bluegill capturing treated and untreated prey increased significantly with copper concentration and was the most consistently sensitive parameter measured. Capture efficiency by bluegill, although altered by copper for some prey types, was not as consistent a measure of toxicant stress. This study suggests that mechanistic measures are valuable indicators of toxicant effects on fish feeding behavior and that copper concentrations near the U.S. Environmental Protection Agency water quality criteria (18–28 μ L−1) may alter food consumption and reduce growth of fish in the wild.