Avoidance of aluminum by rainbow trout

Aluminum is the principal toxicant in fish in acid waters. The ability to avoid Al, particularly at low concentrations, would confer a considerable ecological advantage, but previous research into avoidance of Al has produced mixed results. I used a cylindrical perspex tank, 150 cm in length, to study avoidance of Al by rainbow trout fry. The fish avoided Al, and their response was dependent on pH. Avoidance that was demonstrated at pHs of 5.00, 5.50, and 5.75 was abolished at a pH of 6.00. Fry avoided very low Al concentrations, being sensitive to [Al] > 1.00 μmol L−1 at a pH of 5.00. This unequivocal demonstration of avoidance by rainbow trout fry of Al may have important implications for the ecology of indigenous fish populations in surface waters impacted by acidic deposition.