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

¹ LERMA, INTECHMER/CNAM, BP 324, 50103 Cherbourg Cedex, France
² IFREMER, place Gaby Coll, BP 7, 17137 L’Houmeau, France
³ Station expérimentale d’Aquaculture Ifremer, Laboratoire de Recherche piscicole de Méditerranée, chemin de Maguelone, 34250 Palavas-les-Flots, France

^a Corresponding author: david.benhaim@cnam.fr

Received: 30 March 2011
Accepted: 24 July 2011

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.