INFLUENCE OF PREVIOUS EXPERIENCE ON THE FEEDING-HABITS OF LARVAL WEAKFISH CYNOSCION-REGALIS

Larval weakfish Cynoscion regalis (Bloch & Schneider) were examined to determine the influence of dietary conditioning on prey selection. Experiments were conducted with larvae in each of 4 age classes (8, 11, 14 and 17 d posthatching). Larvae were given a monospecific diet of either large rotifers, small rotifers, or brine shrimp nauplii for 5 d prior to an experiment. Larvae were then given a choice between the familiar prey and one of the other prey types. In separate experimental trials, the conditioned prey was administered in 3 different proportions (10, 25 or 40 %) of the total ration. Larvae consumed both prey types in all trials, but analysis of gut contents often showed a significant deviation from expected ratios of the 2 prey. In experiments with the 2 size classes of rotifer, all ages of larvae chose the familiar prey. In the large rotifer/brine shrimp experiments, larvae 11 and 14 d posthatching could be conditioned to large rotifers; however, larvae 17 d posthatching always chose brine shrimp, even when initially conditioned to rotifers. In comparisons of small rotifers and brine shrimp, larvae never showed a preference for rotifers. These results indicate that effects of dietary conditioning on prey selection vary with larval age and relative prey size.