Mortality of Walleye Eggs and Rainbow Trout Yolk-Sac Larvae in Low-pH Waters of the LaCloche Mountain Area, Ontario

Publisher Website
Google Scholar
Abstract
Freshly fertilized eggs of S. vitreum were incubated in the outlet waters of George Lake (pH 5.4) and sections of a nearby stream (pH 6.0, 6.6). Ten-day bioassays with yolk-sac larvae of S. gairdneri were run concurrently at the walleye sites and at additional sites with low pH (4.6) and with humic water (pH 5.5). Walleye egg mortality was low (25.5-33.5%) at pH 6.0. High mortality (90.5%) occurred between fertilization and the eyed-egg stage at the pH 5.4 site. Mortality of rainbow trout yolk-sac larvae approached 100% within 5 days at both pH 4.6 and 5.4. Total mortality was less than 3% at pH 6.0 and also in low-pH humic water (pH 5.5). The high mortality of walleye eggs in the acidic outlet waters of George Lake suggests that the acidification of this lake was responsible for the extinction of its walleye stock. The striking differences in mortality of rainbow trout yolk-sac larvae between sites of similar pH (5.4-5.5) indicated that H+-toxicity was not solely responsible for fish mortality in acid water. Results draw attention to the effects that biologically available forms of toxic metals, particularly of Al, have on fish survival.