Recovery of Atlantic salmon smolts following aluminum exposure defined by changes in blood physiology and seawater tolerance

Acidification is acknowledged as a cause for extinction or catch reductions in numerous rivers supporting Atlantic salmon (Salmo salar L.) populations in Norway. In freshwater, labile (cationic/inorganic) forms of Al (LAl) accumulate onto and in fish gills, where high concentrations can result in mortality due to respiratory and ionoregulatory dysfunction. At lower concentrations, Al may still have major population effects, mainly through the inhibition of gill Na+,K+-ATPase activity, reducing hypo-osmoregulatory capacity and thereby affecting marine survival. Following episodic exposure, normal smolt properties are expected to be restored. In 2006 and 2007 we exposed groups of 1100 to 1200 one-year old hatchery reared, Carlin tagged Atlantic salmon smolts of the Imsa strain (South-Western Norway) to moderately acidified water (pH 5.6–5.7; 10–15μgL All−1) for 2 to 14days whereupon they were transferred to a water quality assumed to be satisfactory for smolt (good water; pH 6.8–7.2 and