Water quality requirements of smolting Atlantic salmon (Salmo salar) in limed acid rivers

Frode Kroglund and Magne Staurnes
Can. J. Fish. Aquat. Sci./J. Can. Sci. Halieut. Aquat. 56(11): 2078-2086 (1999)

Abstract: Groups of Atlantic salmon (Salmo salar) smolts were held 1-13 days in soft water with a pH range of 5.0-6.6, concentrations of labile inorganic monomeric Al (Al_i) of 10-90 µg·L^-1, and 0.7-2.3 mg Ca·L^-1. Fish were exposed to either naturally acidic water from a river in southwestern Norway, limed water from the same river, mixtures of acidic and limed river water, acidic river water with sulfuric acid and Al added, or limed river water with additional lime. Mortality was observed in all groups exposed to water with pH < 5.8 and containing 30-90 µg Al_i·L^-1. No fish died in water with pH > 5.8 and 15-20 µg Al_i·L^-1, but fish in water with pH 5.8-6.2 had lower plasma Cl^- concentration and gill Na⁺,K⁺-ATPase activity than fish in water with pH > 6.5. Smolts exposed to pH < 5.8 were unable to survive in seawater, and smolts exposed to water with pH 5.8-6.2 had lower hypoosmoregulatory capacity than smolts exposed to water with pH > 6.5. These results show that even moderately acidified water with low Al concentrations impairs smoltification and reduces the seawater tolerance of Atlantic salmon smolts.