Aluminum and Acid Toxicity to Two Strains of Brook Trout (Salvelinus fontinalis)

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Abstract
Two strains of 1-yr-old brook trout were exposed to 14 combinations of pH, aluminum, and calcium during a 28-d experiment. Survival, weight, and gill histology of both strians were affected similarly by pH, aluminium and calcium exposure. Survival was reduced at inorganic monomeric aluminum concentrations (IA1) of 29 .mu.g/L at pH 5.2 and .gtoreq. 228 .mu.g/L at pH 4.4 and 4.8. Fish weight was reduced with exposure to pH below 4.8 or aluminum concentrations .gtoreq. 34 .mu.g/L. The gills sampled from fish exposed to low pH exhibited lifting of the outer epithelium and hypertrophy (increase in size) of chloride and epithelial cells. The response of gills sampled from fish exposed to low pH and elevated aluminum was more pronounced relative to the low pH exposure alone. In addition to the effects observed in the low pH exposed fish, the gills from fish exposed to both acid and aluminum exhibited vacuolation and degeneration of epithelial and chloride cells and the presence of dense cells. Finally, fish confined in PVC tubes designed to mimic in situ field exposure procedures were more sensitive to the toxic effects of acid and aluminum compared to free-swimming fish. Caution must be taken when extrapolating safe field levels from in situ exposures of caged fish.