EFFECT OF LARVAL DENSITY AND FOOD AVAILABILITY ON THE BEHAVIOR OF PRE-METAMORPHOSIS SNAPPER, PAGRUS-AURATUS (SPARIDAE)

The effect of larval density and food availability on the behaviour of 27-day-old (6.01 +/- 0.31 mm total length) pre-metamorphosis snapper larvae, Pagrus auratus, was studied over a seven-day period. Five dens ities (5, 15, 30, 45 and 60 larvae L(-1)) and two feeding regimes (0.5 Artemia nauplii mL(-1) and a proportional density-dependent feeding r egime) were tested in a factorial design experiment. Behaviour was gro uped into three nested duration events (swimming, resting and feeding) and four non-nested frequency contact events, viz. startle response a nd non-aggressive contacts (non-aggressive frequency events) and body- bites and head-on aggression contacts (aggressive frequency events). R esting duration was found to be independent of food availability but s ignificantly dependent on larval density. There were highly significan t interactions between larval density and the two feeding strategies, indicating that snapper larvae feed more actively, at a high populatio n density, at high levels of food availability. The frequency of aggre ssive and non-aggressive events during the feeding mode was significan tly dependent on larval density but independent of food availability. During the swimming mode, only startle responses and body-bite contact s were dependent on larval density, whereas all frequency events were independent of food availability. Significantly higher percentages of aggressive contact events were recorded during the feeding mode than d uring the swimming mode. The results suggest that live food should be provided on the basis of constant availability per larva.