Low concentrations of inorganic monomeric aluminum impair physiological status and marine survival of Atlantic salmon

Two strains of Atlantic salmon (Salmo salar) presmolts were exposed for 3 months to moderately acidic water (pH 5.8; 6 +/- 2 mug aluminum (Ali) l(-1) inorganic monomeric aluminum-acid exposure group) or non-acid water (pH > 6.5 -6.9; < 5 mug Ali l(-1)-Good/control group) at NINA Research Station, Ims, Southern Norway. Exposure to low concentrations of Ali raised the gill-aluminum (gill-Al) concentration by 20-30 mug At g(-1) gill dry weight compared to control fish having < 10 mug Al g(-1) gill dry weight. The fish responded to the At loading with elevated blood glucose, but retained more normal hematocrit and plasma chloride levels. Fish exposed under acid conditions grew significantly poorer than the control fish. After 3 months of exposure, 150 Carlin-tagged smolts from both Imsa treatments were released into the non-acidic River Imsa, 800 in upstream from a trap that caught all migrating smolts. Acid-exposed fish migrated downstream slightly later than the controls. At the same time, Carlin-tagged fish from all four treatments (Acid and Good, both strains; approximately 1000 fish group(-1)) were released downstream of the trap located 150 in above the river mouth. Based on the number of adult recaptures (by May 2001), marine survival was 20-30% lower for the acid-exposed fish than for the controls. There were no differences in marine growth between the treatments. The results suggest that even very low concentrations of Ali (6 +/- 2 mug l(-1)) can reduce seawater survival, thereby having effect on the population level. The physiological responses, reduced growth and reduced marine survival also suggest that the presmolts did not acclimate to the acid conditions. (C) 2003 Elsevier Science B.V. All rights reserved.