Effect of dietary energy content on gilthead sea bream (Sparus aurata) feeding behaviour and nutritional use of the diet

Abstract

We have studied how the diet energy level affects gilthead sea bream (Sparus aurata) daily pattern of demand-feeding activity and nutritional use of the diet under summer- and winter-like conditions. To that end, animals were kept in a closed circuit under controlled temperature and photoperiod, and fed one of two commercial diets with either high (H: 238 g kg[superscript [-]1] fat) or low (L: 172 g kg[superscript [-]1] fat) energy content. In summer conditions (26 °C; 12 : 12 L : D), both diets yielded similar growth rate (0.7 ± 0.0 and 0.7 ± 0.1) and thermal unit growth coefficient values (0.6 ± 0.0 and 0.6 ± 0.0), and although the daily rate of delivered feed was somewhat higher for fish under the high-energy diet (16 ± 2 g kg[superscript [-]1] of fish) the difference was not significant. In winter conditions (17 °C; 9 : 15 L : D), on the other hand, no differences were found for any of the parameters evaluated. Thus, the higher lipid content of the diet does not appear to have any protein sparing effect. The 'summer' demand-feeding pattern displayed three daily peaks, which were quite apparent for fish under the low-energy diet, but rather smoothed for those that ate the energy-rich diet. This profile was replaced in winter conditions by a single peak around noon, and the animals also displayed a lower overall number of demands.