Differences in the pattern of antipredator behaviour between hatchery-reared and wild European sea bass juveniles

Shoals of hatchery-reared and wild sea bass juveniles Dicentrarchus labrax were tested for differences in their antipredator responses towards a potential live predator, the eel Anguilla anguilla. Eight experimental shoals (i.e. replicates), each composed of 15 individuals from the same stock of juveniles (i.e. wild or hatchery), were video recorded for 5 min before and after predator exposure. A set of behavioural variables were measured during the pre-stimulus and stimulus phases of each test and compared between the two groups of replicates. Results showed that in both hatchery-reared and wild juveniles predator exposure elicited a significant increase in the mean level of shoal cohesiveness and mean shoal distance from the predator, and a significant decrease in the mean shoal distance from the bottom. Shoals of wild juveniles, however, aggregated more quickly and reached higher shoal cohesiveness within the first 20s of the stimulus period than shoals of hatchery-reared fish. During this period, the wild fish also reached the highest peak in shoal cohesiveness, which then decreased gradually towards the levels observed before predator exposure. Another component of the antipredator response, the predator inspection behaviour, was fully developed in both wild and hatchery fish. Wild fish, however, tended to inspect the predator at a closer distance than hatchery fish. (C) 2004 The Fisheries Society of the British Isles.