Copper metabolism and gut morphology in rainbow trout (Oncorhynchus mykiss) during chronic sublethal dietary copper exposure

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to 11 (control), 300 (medium), and 1000 mug Cu.g(1) (high) (as CuSO(4)5H(2)O) in the diet for 28 days at a daily ration of 4% wet body weight, with a background waterborne Cu concentration of 3 mug.L-1. There was no effect of dietary Cu on growth, condition factor, or food conversion efficiency. Whole-body Cu content increased continuously over the exposure period in all groups and was twofold and fourfold higher than controls at day 28 for the medium- and high-Cu diets, respectively. Copper accumulated mainly in liver and gut tissue, with the latter stabilizing by day 14. Accumulation also occurred in gill, kidney, and carcass. Plasma Cu concentration was not different from the controls whereas Cu in bile was greatly elevated, an indication of increased hepatobiliary excretion. Dietary Cu pre-exposure decreased the uptake of waterborne Cu across the gills, providing the first evidence of homeostatic interaction between the two routes of uptake. Electron microscopic observations of the midintestine revealed numerous mitochondria, lysosomes, lamellated bodies, and extensive lamellar processes in the enterocytes. Apoptosis, mitosis, and eosinophilic granule cells were more apparent in Cu-exposed fish.