Mechanism of copper tolerance in black-banded rainbowfish (Melanotaenia nigrans) from the East Branch, Finniss River

Mining is a common cause of copper pollution in the aquatic environment. Several studies have demonstrated the ability of fish to develop copper tolerance in the laboratory following sublethal exposure (Dixon and Sprague, 1981; Buckley et al., 1982; Taylor et al., 2000). In this study, the bioconcentration of 64/67Cu was used to investigate the mechanism of copper tolerance in exposed fish. Both exposed and reference fish were exposed to low (30 mg L-1) and elevated (300 mg L-1) copper concentrations for 24 and 48 h, respectively. Radioactivity was measured in four tissue sections: head region (gills, heart and brain), internal organs (including the gastrointestinal tract, liver, kidneys and gonads), muscle section, and whole body. Radioactivity correlated to the total copper concentration in the tissue section. One-compartment bioconcentration models were fitted to data for reference and exposed fish and the regressions compared using an F-test. It was found that the reduced copper accumulation by exposed fish was due to reduced copper uptake, and as the gills are the primary site of copper uptake, the mechanism of reduced uptake is likely to occur there. Reduced gill uptake in exposed fish may have been due to changes in gill binding sites, gill surface area or gill mucus secretion rates, compared to reference fish