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