Are chemical alarm cues conserved within salmonid fishes?

A wide diversity of fishes possess chemical alarm signalling systems. Howev er, it is not known whether the specific chemicals that act as alarm signal s are conserved within most taxonomic groups. In this study we tested wheth er cross-species responses to chemical alarm signals occurred within salmon id fishes. In separate laboratory experiments, we exposed brook charr (Salv elinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhyn chus mykiss) to chemical alarm signals from each of the three salmonid spec ies and from swordtails (Xiphophorus helleri). In each case, the test speci es responded with appropriate antipredator behavior to all three salmonids alarm cues, but did not react to swordtail cues. These data suggest that ch emical alarm cues are partially conserved within the Family Salmonidae. For each species tested, the intensity of the response was stronger to conspec ific alarm cues, than to heterospecific alarm cues, indicating that salmoni ds could distinguish between chemical cues of conspecifics versus heterospe cifics. These results suggest that the chemical(s) that act as the alarm cu es may be: 1) identical and that there may be other chemical(s) that allow the test fish to distinguish between conspecifics and heterospecifics, or 2 ) that the cues that act as signals are not identical, but are similar enou gh to be recognized.