Toxicity of environmental acid to the rainbow trout: interactions of water hardness, acid type, and exercise

Abstract

Classical 7-day lethality tests were used to establish the influence of water hardness (.simeq. 140 vs. .simeq. 14 mg/l CaCO3), acid type (HCl vs. H2SO4) and activity level (rest vs. exhaustive exercise) on acid toxicity to fingerling rainbow trout (S. gairdneri) at 15.degree. C. Seven-day mean lethal concentration (LC50) pH ranged from 4.1-4.5. Hardness reduced H2SO4 toxicity at all pH levels during rest and exercise, but reduced HCl toxicity only at very low pH levels. Hardness increased HCl toxicity at pH > 3.8. H2SO4 was generally less toxic than HCl, except at pH > 3.8 in soft water. Exhaustive exercise markedly potentiated H2SO4 toxicity in hard and soft water except at very low pH levels. Below pH = 4.4-4.6, critical swimming speed declined linearly by .apprx. 4% per 0.1 pH unit. Possible physiological mechanisms responsible for these modifying influences and their ecological significance are discussed.