Acquired predator recognition in juvenile rainbow trout (Oncorhynchus mykiss): conditioning hatchery-reared fish to recognize chemical cues of a predator

In this study, we exposed predator-naive, hatchery-reared juvenile rainbow trout (Oncorhynchus mykiss) to the chemical stimuli from northern pike (Esox lucius) and either trout skin extract (a chemical alarm signal) or a distilled water control to test for acquired recognition of a novel predator. Trout exposed to conspecific skin extract and pike odour significantly increased antipredator behaviour (i.e., decreased foraging and area use and increased shoaling and freezing), while those exposed to distilled water and pike odour did not. Conditioned trout were exposed to pike odour alone (versus a distilled water control) either 4 or 21 days later. When presented with pike odour 4 days postconditioning, trout significantly increased antipredator behaviour (i.e., decreased foraging and area use and increased time under cover and freezing). Trout tested 21 days postconditioning still exhibited a significant increase in antipredator behaviours when presented with pike odour alone (i.e., decreased foraging and increased freezing). These data are the first to demonstrate that hatchery-reared trout can be conditioned to recognize the chemical cues of a predator and suggest that this may serve as a strategy to train hatchery-reared fish to recognize predators prior to stocking into natural waterways.