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Dietary uptake of copper in freshwater rainbow trout (Oncorhynchus mykiss): A study of mechanisms

In aquatic environments Cu is both a vital nutrient and an important toxicant. Consequently fish require Cu as a micronutrient and can obtain this metal from either water or their diet. Inadequate intake of Cu is associated with reduced growth and development, while decreased growth rates, mortality and reduced swimming capacity have been reported in fish when Cu accumulates in excess of cellular needs. Characterization of Cu uptake is therefore critical in understanding the dynamics that govern toxicity and the risks associated with exposure to an aquatic contaminant. While mechanisms of waterborne uptake and toxicity are well understood, far less is known about gastrointestinal Cu uptake in fish. In vivo and in vitro techniques were therefore used in this study to investigate dietary Cu uptake in freshwater rainbow trout. The mid and posterior regions of the intestine emerged as important sites for Cu absorption in trout, while the role of the stomach and anterior intestine in Cu absorption requires further investigation. The intestinal uptake route was kinetically characterized as a low affinity absorption pathway as compared to the branchial route. Cu uptake appeared to occur via a hypoxia-resistant, carrier-mediated, saturable process which could be fueled by Cu(IIi+ at concentrations typically found in the fluid phase of chyme in the trout intestine. Experimental manipulation of mucosal NaCllevels stimulated Cu uptake, Na2S04 had an identical effect, implicating N a rather than the anion. These responses were unrelated to solvent drag, osmotic pressure or changes in TEP. The presence of excess