MORTALITY, GROWTH, SWIMMING ACTIVITY AND GILL MORPHOLOGY OF BROOK TROUT (SALVELINUS-FONTINALIS) AND ATLANTIC SALMON (SALMO-SALAR) EXPOSED TO LOW PH WITH AND WITHOUT ALUMINUM

Measurements were made of mortality, growth, swimming activity, and gi ll morphology of young-of-the-year brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar), exposed for 30 days to pH 5.6 +/- 0.5 (mean +/- 1 standard deviation) with and without addition of 107 /- 57 mu g liter(-1) exchangeable (labile monomeric) aluminum. The exp eriment was conducted in artificial stream channels adjacent to a natu ral stream and subject to daily and seasonal changes in temperature, l ight, and chemical conditions. There were no differences in survival o r growth for brook trout in any treatment; Atlantic salmon survival an d growth were significantly decreased in the acid + Al treatment. Scan ning electron microscopy showed no damage to gills of either species i n the acid treatments, but the acid + Al treatment caused slight swell ing of brook trout gills near the filament tips and significant swelli ng and fusion of secondary lamellae of Atlantic salmon gills. The acid treatment increased swimming activity in brook trout, but both the ac id and acid + Al treatments reduced activity in Atlantic salmon.