Threat-sensitive learning of predator odours by a prey fish

Many prey animals have a remarkable ability to match the intensity of their behavioural responses to the degree of threat posed by specific predators. However, little is known about bow such threat-sensitive predator avoidance develops. In a series of laboratory experiments we tested whether goldfish (Carassius auratus) could learn to recognize predator odours in a threat-sensitive manner. We exposed predator-naive goldfish to various concentrations of chemical cues of pike (Esox lucius) fed goldfish and pike fed another fish diet (swordtails, Xiphophorus helleri). During the conditioning trials goldfish showed behavioural responses to pike fed goldfish but not to pike fed swordtails. Moreover, the intensity of the responses to pike cues increased as the concentration of pike cues increased. Subsequent test trials showed that goldfish that had originally been exposed to pike fed goldfish showed responses to pike fed swordtails, indicating learned recognition of the pike as a predator. Of particular importance, the intensity of the learned responses by the goldfish matched the intensity of the responses observed in the original conditioning trials, thereby demonstrating threat- sensitive learning. Prey should have a selective advantage if they are able to adjust the intensity of their anti-predator response to match the threat posed by their predators. Our preliminary investigations revealed that this threat-sensitive learning has important survival implications during encounters with pike.