Differences in acid tolerance during the early life stages of three strains of brook trout, Salvelinus fontinalis

Abstract

Brook trout, Salvelinus fontinalis, embryos and fry from three sources (an acidic watershed in Kejimkujik Park at pH 4.7 to 5.3, a neutral watershed at pH 7, a hatchery at pH 7) were exposed separately to lethal and sublethal levels of acidity (pH 7.0, 5.2, 4.7, 4.3, 3.9), beginning at fertilization. Significant differences in mortality between the strains at low pH were observed and these suggested a genetic component to acid tolerance. Mortality in the strain from the acidic watershed was the lowest, followed by the second wild strain. Survival in both wild strains at low pH was much better than survival in hatchery embryos. These differences in survival at sublethal acidity (4.7 to 7.0) were principally the result of high mortality shortly after fertilization. After this period, survival stabilized. Only at pH 4.3 did substantial mortality occur at hatching. The early embryonic stage therefore appears to be the most susceptible to sublethal acid stress in brook trout. Hatchery strain embryos were also introduced at the eyed stage at 213 degree-days. Subsequent survival of this group was better at low pH than that of hatchery embryos introduced at fertilization, thereby indicating an early or cumulative deleterious effect. Higher acidity retarded hatch in all cases. The time to 50% hatch was delayed by 1.2 degree-days with each increase of 1 μM H+.