Effects of pH, aluminum, and calcium on survival and growth of eggs and fry of brook trout (Salvelinus fontinalis)

Freshly fertilized eggs, eyed eggs, yolk-sac fry, and swim-up fry of brook trout were exposed to a matrix of 84 combinations of pH (4.0-6.5), Al (0-1000 μg/L), and Ca (0.5-8.0 mg/L) in 21-91 d experiments. Sensitivity to acid toxicity generally decreased with age (freshly fertilized eggs>eyed eggs>yolk-sac fry=swim-up fry). Survival or hatching of freshly fertilized and eyed eggs decreased ≤pH 5.2; survival of yolk-sac and swim-up fry was reduced at pH 4.4-4.0. Sensitivity to Al toxicity generally increased with age (freshly fertilized eggs=eyed eggs<yolk-sac fry<swim-up fry). At low pH, survival of freshly fertilized and eyed eggs increased with exposure to increasing Al concentrations. Elevated Al (≥333 μg/L) was often toxic to fry. Increasing Ca was beneficial to all life stages, although the magnitude of this benefit depended on life stage and on the specific pH and Al concentration. Survival after previous exposure to toxic combinations of pH, Al and Ca generally improved during a post-exposure recovery period at pH 6.5, but increased mortality in many exposure combinations did not begin until this recovery period. -from Authors