• acid rain;
  • antipredator behaviour;
  • centrarchids;
  • chemical alarm cue;
  • hypoxanthine-3-N-oxide;
  • pumpkinseed

Under neutral (pH 7·0) conditions, juvenile pumpkinseed Lepomis gibbosus exhibited significant antipredator responses, of similar intensities, to the chemical alarm cues of conspecifics, an allopatric congener the green sunfish Lepomis cyanellus and the artificial alarm cue of a sympatric prey guild member (Cyprinidae, hypoxanthine-3-N-oxide). Under weakly acidic conditions (pH 6·0), however, no increase in antipredator behaviour was seen in response to hypoxanthine-3-N-oxide and a quantitatively weaker response was found in response to conspecific and congener cues, suggesting that the use of chemical alarm cues by some prey fishes may be impaired by acid precipitation.