Oxygen Consumption as a Function of pH in Three Species of Freshwater Fishes

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The routine rate of oxygen consumption (V/sub O/sub 2//) was measured over an H/sub 2/SO/sub 4/ pH range of 3.5 to 7.0 for three species of freshwater fishes previously exposed for at least two weeks to pH 7.5 or 5.0. V/sub O/sub 2// was also measured at pH's from 4.0 to 7.0, in increments of 0.5 pH units, for each species after maintenance at the measurement pH. Preliminary tests showed that acute exposure to pH 3.5 (H/sub 2/SO/sub 4/) was lethal to all three species, and that only Lepomis macrochirus could survive exposure to 4.0 for at least two weeks. V/sub O/sub 2// did not show any significant decrease at pH's below 5.0 in Lepomis macrochirus or Carrasius auratus, but was significantly depressed in Ictalurus punctatus at pH 3.5. These results suggest that the importance of anoxia as a factor contributing to the death of fishes at low pH may vary among species. Mining operations and acid precipitation have produced large numbers of lakes and watersheds that undergo either chronic or acute episodes of low pH.