Socially-induced changes in sodium regulation affect the uptake of waterborne copper and silver in the rainbow trout, Oncorhynchus mykiss

Subordinate fish take up more copper during water-borne exposure than dominant fish and consequently display higher tissue burdens. The present study demonstrated a similar effect of social status on water-borne silver uptake. We evaluated whether differences in copper and silver accumulation between individuals could be due to differences in metabolic rate, internal concentrations of cortisol or sodium uptake rates. In the absence of social interaction, experimentally increased metabolic rates (via moderate exercise) and elevated whole body cortisol concentrations (via feeding of a cortisol-spiked diet) did not result in increased metal uptake. However, elimination of the difference in sodium uptake rates between dominant and subordinate fish by exposing them to a saturating level of water-borne sodium (50 mM) resulted in an elimination of copper uptake differences. No significant differences in sodium and silver uptake rates were seen between dominant and subordinate fish exposed to elevated silver concentrations. Therefore, it appears that socially-mediated differences in copper and silver accumulation are a result of differences in sodium uptake rates as both silver and copper are known to cross the gill epithelia via sodium transport pathways.