Growth heterogeneity in rearing sea bass ( Dicentrarchus labrax): test of hypothesis with an iterative energetic model.

This study aimed at modeling the relative importance of food intake on growth heterogeneity among cultured sea bass (Dicentrarchus labrax). First, we designed an individual growth model comprising five compartments (Energy intake, Losses, Net Energy, Recovered Energy and Maintenance). This model was calibrated with a first experiment carried out in eight tanks; A total of 130 juveniles (11 g) per tank were fed by a self-feeder (84 days, 20°C, 16L : 8D, 30 g NaCl/l). A second experiment was performed to better understand the relation between individual food intake, individual growth and growth heterogeneity, using the model as a tool for a hypothetico-deductive approach on growth heterogeneity (135 passive integrated transponder-tagged fish, same rearing conditions as above and individual food intake measured by X-ray every 14 days). The tested hypotheses were that food intake was (a) homogeneous, (b) proportional to the fish weight (i.e. to W1.00) X-ray (c) proportional to W0.66 and (d) reflected by the X-ray measurements of food intake. For each hypothesis, a simple linear regression between experimental and simulated results was produced. The Fitness indicators of these analyses, together with their confidence intervals (calculated by bootstrapping), allowed testing the relevance of these hypotheses. The analysis indicated that growth heterogeneity was largely accounted for by individual variations of food intake, as revealed by the X-ray analysis, and that food intake was proportional to W1.00, which suggests a dominance hierarchy where small fish are incapable of feeding maximally.