EFFECTS OF CADMIUM ON THE FORAGING BEHAVIOR AND GROWTH OF JUVENILE BLUEGILL, LEPOMIS-MACROCHIRUS

Standardized test protocols for assessing chemical hazards to aquatic organisms inadequately consider behavioral effects of toxicants; yet, organisms behaving abnormally in the wild have reduced growth, reduced fitness, and high mortality. We determined the chronic effects of cad mium (0, 30, 60, 120, and 240 mu g . L(-1)) on juvenile bluegill (Lepo mis macrochirus) foraging behavior and growth rates in functional resp onse experiments, each using different sized Daphnia as prey. Bluegill consumption rate increased with prey density. Cadmium-exposed fish in itially attacked fewer prey per unit of time than unexposed fish, with subsequent recovery to control-level consumption rates determined by cadmium concentration and prey size. The degree of change (over time) in the number of Daphnia attacked per 30 s was the most consistently s ensitive behavioral measure of sublethal stress in exposed bluegill; t he lowest observed effect concentration (LOEC) was 37.3 mu g Cd . L(-1 ). Effects on prey attack rates (attacks/30 s) were inversely related to prey size; cadmium had the greatest effect on bluegill foraging on the smallest prey. Cadmium had no effect on prey capture efficiency or handling time. Growth in bluegill length and weight was reduced (P le ss than or equal to 0.019) by all cadmium concentrations and was a mor e sensitive end point than were the foraging behaviors.