Branchial and renal ion fluxes and transepithelial electrical potential differences in rainbow trout, Oncorhynchus mykiss: effects of aluminium at low pH

Adult rainbow trout, Oncorhynchus mykiss, were acutely exposed for 4 hours to low pH (4.4) and elevated Al-concentrations (300 μgI^-1) in soft water (Ca²⁺ + Mg²⁺ = 25 μmolI^-1). Comparison of branchial and renal ion fluxes (Na⁺, Cl^-, Mg²⁺, Ca²⁺ and NH₄⁺) gave evidence that pH and Al effects were primarily localized at the gill site. The negative whole body ion balance seemed to be caused by stimulatory effects on Na and Cl efflux especially under Al stress and to a lesser extent by inhibition of influx. Measurements of gill potentials indicated positive shifts, which were similar in response to increasing levels of H⁺ ions and Al. It is suggested that Al-induced changes of branchial potentials causes high diffusable loss of ions through interference with membrane-bound Ca²⁺ at the gill site.