Conditioning Hatchery-Reared Fish to Recognize Non-Native Predators

Predation by non-native fish may be the main mortality source for stocked bonytail (Gila elegans) and razorback sucker (Xyrauchen texanus) in the Lower Colorado River. Hatchery reared fish are naive to this risk and may not survive their first encounter with a predator. We used conspecific prey alarm pheromone to condition groups of predator-naive prey fish to recognize a non-native fish predator. Prior to conditioning, the jaw muscle of a predator fish was incapacitated with botulinum toxin, preventing it from capturing prey fish during conditioning. Fish were conditioned by simultaneously adding a hindered predator and alarm pheromone into their tank. Predator recognition conditioning significantly improved survival of bonytail and razorback in 24 hour survival trials with largemouth bass (Micropterus salmoides), channel catfish (Ictalurus punctatus), and mixed bass and catfish. Survival of conditioned fish averaged 20% higher than unconditioned fish. There was no change in mean prey fish size, suggesting that all prey fish were susceptible to predation and conditioning benefitted all prey fish sizes. This novel conditioning method improved survival without prey fish seeing or experiencing predation during the conditioning process, suggesting this methodology may be successful at training large groups of these endangered fish in hatchery production ponds.