The effect of aluminium in soft water at low pH and different temperatures on mortality, ventilation frequency and water balance in smoltifying Atlantic salmon, Salmo salar

Salmon smolts were exposed to acidic aluminum-rich water at varying temperatures to assess the effects on mortality, ventilation frequency, and water balance. Water temperature, conductivity, pH, and the quantities of inorganic and organic Al species were monitored daily throughout the experiment. All fish exposed to water at pH 5.0 and 235 mu g/l Al died within 80 h. Mortality increased directly with increasing temperature. Under these conditions, ventilation frequency was higher than controls, and the fish lost plasma chloride and sodium ions throughout the experimental period. Plasma osmolality decreased throughout exposure, and hematocrit increased. The results indicate that fish exposed to pH 5.0 and temperatures above 10 degree C may suffer from a combination of hypoxia and electrolyte loss because of enhanced polymerization of Al onto gill surfaces.