BRIEF COMMUNICATIONS Detection of conspecific and heterospecific alarm signals by juvenile pumpkinseed under weak acidic conditions A. O. H. C. L EDUC *†, M. K. N OSEWORTHY *, J. C. A DRIAN J R ‡ AND G. E. B ROWN * *Department of Biology, Concordia University, 7141 Sherbrooke St W., Montreal, Quebec, H4B 1RS, Canada and ‡Department of Chemistry, Science and Engineering Center, Union College, Schenectady NY, 12308, U.S.A. (Received 20 November 2002, Accepted 6 August 2003) 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 con- specific and congener cues, suggesting that the use of chemical alarm cues by some prey fishes may be impaired by acid precipitation. # 2003 The Fisheries Society of the British Isles Key words: acid rain; antipredator behaviour; centrarchids; chemical alarm cue; hypoxanthine- 3-N-oxide; pumpkinseed. Damage-released chemical alarm cues have been demonstrated in a wide variety of fishes, including ostariophysans, salmonids, gobies, poecilids, sticklebacks, percids, cottids, cichlids and centrarchids (Chivers & Smith, 1998; Golub & Brown, 2003). When detected by nearby conspecifics (and some sympatric heterospecifics), these chemical cues elicit dramatic short-term increases in species typical antipredator behaviours (Chivers & Smith, 1998). Detecting chemical alarm cues from conspecifics and sympatric heterospecifics confers significant survival benefits to individuals (Mirza & Chivers, 2001; Chivers et al., 2002). In addition, aquatic predators have been shown to use these chemical signals as foraging cues (Mathis et al., 1995; Brown et al., 2001). Thus, any impairment in an individual’s ability to detect these chemical alarm cues should have significant impacts on survival and long-term fitness potentials. †Author to whom correspondence should be addressed. Tel.: þ1 514 848 4020; fax: þ1 514 848 2881; email: aleduc@alcor.concordia.ca Journal of Fish Biology (2003) 63, 1331–1336 doi:10.1046/j.1095-8649.2003.00230.x, available online at http://www.blackwell-synergy.com 1331 # 2003 The Fisheries Society of the British Isles