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 fo r 28 days at a daily ration of 4% wet body weight, with a background waterb orne Cu concentration of 3 mug.L-1. There was no effect of dietary Cu on gr owth, condition factor, or food conversion efficiency. Whole-body Cu conten t increased continuously over the exposure period in all groups and was two fold and fourfold higher than controls at day 28 for the medium- and high-C u diets, respectively. Copper accumulated mainly in liver and gut tissue, w ith the latter stabilizing by day 14. Accumulation also occurred in gill, k idney, and carcass. Plasma Cu concentration was not different from the cont rols whereas Cu in bile was greatly elevated, an indication of increased he patobiliary excretion. Dietary Cu pre-exposure decreased the uptake of wate rborne Cu across the gills, providing the first evidence of homeostatic int eraction between the two routes of uptake. Electron microscopic observation s of the midintestine revealed numerous mitochondria, lysosomes, lamellated bodies, and extensive lamellar processes in the enterocytes. Apoptosis, mi tosis, and eosinophilic granule cells were more apparent in Cu-exposed fish .