The behavioural responses of Nile tilapia (Oreochromis niloticus) to anti-predator training

Globally millions of fishes are released, each year, into the wild to supplement diminishing populations. However, research indicates that less than 5% of these individuals survive, and that one of the major causes of mortality is predation. The objective of the experiment was to develop a protocol to train captive born and reared fish how to avoid predators. The protocol consisted of showing a model predator to group housed fish and then associating the predator with an aversive stimuli (simulated capture with an aquarium net). We trained, in 27 sessions, four groups of 35 Nile tilapia using this method, and had four Control groups of equal sizes. The Control groups were presented with the predator model only once, and this presentation was not associated with the aversive stimuli. The results showed that the behaviour of Conditioned fish was modified in an adaptive form after only three training sessions. After 12 training sessions the Conditioned fish expressed a new anti-predator response (rising to and freezing at the surface of the water). The Control fish responded to the model predator as if it were a novel object rather than a predator; that is, initially they showed a fear response that quickly waned. A Memory test was conducted on the trained fish 75 days after their last training session, and this showed that some of the fishes had retained the behavioural responses they had acquired during their training. In conclusion, the results of this experiment show that behavioural conditioning of captive born and reared fish to avoid their predators in supplementation programs has much potential.