Effect of size grading on sea bass (Dicentrarchus labrax) juvenile self-feeding behaviour, social structure and culture performance

Abstract

This study aims to test the influence of size grading on self-feeding behaviour, social structure (measured by the percentage of triggering acts per individual), growth performances, and blood physiological variables of individually passive integrated transponder (PIT)-tagged sea bass juveniles, using a computerized on-demand feeding system coupled with a PIT tag monitoring device. Three consecutive periods of 27 days each were compared: a first period (P1) before grading (6 tanks of 100 fish; 40.2 ± 8.9 g) followed by a second period (P2) after grading. The protocol applied aimed to create two groups of fish of similar mean weight but with either a low or a high coefficient of variation of weight (CV w) corresponding to an imposed difference in social disruption (T low: CV w ∼ 10%, 3 tanks of 60 fish each with social disruption; T high:CV w ∼20%, 3 tanks of 60 fish each, without social disruption). T low and T high groups were studied over P2, and an additional 27-day period under identical conditions (P3). The grading protocol used and/or time modified the social structure when comparing P1 and P2. Thereafter, during P2 and P3, no difference could be observed in growth performances, feed demand, or physiological variables between T low and T highgroups. Feeding rhythms and social structures were similar in both groups. In conclusion, such grading practice only transiently modifies feed demand behaviour and social structure built around the self-feeder, without further improvement in individual growth performances in sea bass. © 2011 EDP Sciences, IFREMER, IRD.