Effects of waterborne cadmium on metabolic rate, oxidative stress, and ion regulation in the freshwater fish, inanga (Galaxias maculatus)

The freshwater fish Galaxias maculatus (inanga) is a widespread Southern hemisphere species, but despite its habitation of lowland near-coastal waters with a high potential for cadmium contamination, nothing is known regarding its sensitivity to this toxic trace metal. Acute (96 h) exposures were therefore performed to determine sublethal responses of inanga to waterborne cadmium at a regulatory trigger value (nominally 0.2 μg L⁻¹; measured 1 μg L⁻¹), an environmental level (measured at 2.5 μg L⁻¹), and an effect level (measured at 10 μg L⁻¹). Whole body (tissue remaining following excision of kidney and liver) cadmium burden remained constant up until an exposure concentration of 10 μg L⁻¹, at which point cadmium concentration increased significantly. A transient effect of cadmium on metabolic rate was observed, with an impaired oxygen consumption noted at 2.5, but not 1 or 10, μg L⁻¹. Cadmium did not impair influx rates of either sodium or calcium, and no effects of cadmium on oxidative stress parameters (catalase activity, lipid peroxidation) were noted in the kidney. However, at cadmium concentrations of 2.5 and 10 μg L⁻¹, lipid peroxidation in the liver increased, concomitant with a decline in hepatic catalase activity. These data indicate that there are significant differences in the mechanisms of cadmium toxicity in inanga, relative to better-studied Northern hemisphere species, especially with respect to ionoregulatory impacts. However, effects were induced at cadmium concentrations unlikely to be encountered in any but the most highly contaminated waterways, and thus our data suggest that current trigger values for cadmium concentrations in Australian and New Zealand waters are likely to be protective of inanga.