Field responses of prey fishes to chemical alarm cues

Abstract

A diversity of fishes release chemical cues upon being attacked by a predator. These cues, commonly termed alarm cues, act as sources of public information warning conspecifics of predation risk. Species which are members of the same prey guild often respond to one another's alarm cues. The purpose of this thesis was to discriminate avoidance responses of fishes to conspecific alarm cues and cues of other prey guild members from responses to unknown damaged fish odours and novel odours. I used a series of trap experiments and underwater video observations to measure avoidance responses of freshwater littoral fish species to chemical alarm cues.

In a series of 6 trap experiments I captured fathead minnows (Pimephales promelas) and brook stickleback (Culaea inconstans) in traps containing injured fish cues and novel non-fish odours. In addition to documenting the number of fish present, I also recorded length, weight, body condition, and gonadosomatic index. Despite the large sampling effort it was determined that the study had limited power to detect a 20 % difference in the means between treatments.

Avoidance was tested to both injured fish cues and novel non-fish odours in a camera experiment using fathead minnows, finescale dace (Chrosomus neogaeus), and brook stickleback. The cyprinids (minnows and dace) showed significant avoidance of minnow cues over swordtail cues, morpholine, and the control of distilled water and tended to avoid fathead cues over cues of known prey guild members (stickleback). Cyprinids also significantly avoided cues of stickleback over unknown heterospecific cues (swordtail) and tended to avoid stickleback cues over morpholine and the distilled water control. Stickleback significantly avoided fathead minnow extract over the distilled water and tended to avoid stickleback and swordtail over distilled water. I conclude that fishes in their natural environment can show dramatic changes in behaviour upon exposure to alarm cues from conspecifics and prey guild members. These responses were not the result of avoidance of cues of any injured fish or any novel odour.