Impairment of lake trout foraging by chronic exposure to cadmium: a black-box experiment

Abstract

The foraging success of lake trout ( Salvelinus namaycush) on fingerling rainbow trout ( Oncorhynchus mykiss) was evaluated after both species were exposed to 0.5 and 5 μg Cd l −1 for 8–9 months (up to 277 days). Predation of rainbow fingerlings by lake trout was measured by daily counts of remaining prey in tanks where groups of exposed and unexposed prey fish were presented to exposed and unexposed predators. Using this measure, exposed prey presented to unexposed predators showed slight, but no significant increases in vulnerability to predation. Significant dose-dependent decreases of foraging rates were observed when exposed lake trout were presented with unexposed prey. Of four lake trout tissues sampled, posterior kidney had the highest cadmium concentration reaching 2.5 μg g −1 after 9 months exposure to 5.0 μg Cd l −1. Thyroid follicle epithelial cell height (a measure of thyroid functional state) was significantly decreased at both 6 and 9 months exposure to 5 μg Cd l −1. Results underline a low response threshold for cadmium-caused behavioral changes, determined in a simple, efficient experimental design.