Feeding hatchery-reared dusky grouper Epinephelus marginatus juveniles on live prey: implications for restocking.

Among the behavioural factors affecting survival of hatchery-reared fish when released into the wild, inefficient foraging is considered to be a major behavioural deficit. The present study investigates the ability of hatchery-produced, pellet-reared dusky grouper Epinephelus marginatus juveniles to recognize and catch live prey (sea bass Dicentrarchus labrax fingerlings 30-80 mm TL) and analyses the effects of a training period on their foraging performance. Juvenile E. marginatus (3+ years, 270-330 mm TL) showed an innate ability to recognize and capture live D. labrax fingerlings as latency time to first attack was very short (<1 min). Older and larger-sized juvenile E. marginatus (4+ years, 350-400 mm TL) are not immediately able to recognize live D. labrax as preys and no attack was observed in the first 2 days. A 10 day training period involving live preys improved foraging performance in both younger and older juveniles. The effect was more evident for older E. marginatus in which the ability to recognize prey increased and the latency time to first attack and to first successful attack with experience decreased. For both groups, training also increased the total number of lunges, number of successful lunges and consequently the number of preys eaten. Training should be performed using appropriate sized prey, since smaller-sized E.marginatus prefer smaller preys. Thus, although prey recognition and capture seem to be innate, experience of live prey improves the foraging performance of hatchery-reared E. marginatus of different age-size classes. [ABSTRACT FROM AUTHOR]