Defining the most suitable dietary lipid level in gilthead sea bream, Sparus aurata, reared at high temperature

Gilthead sea bream, Sparus aurata, reared in the Mediterranean Sea are submitted to high temperature during warm seasons and, being poikilotherms, their metabolism is greatly influenced. The aim of this work was to assess the most suitable dietary lipid level to cope sea bream energy request when reared at high temperature. Sixty fish (75 g initial body weight) per tank were randomly distributed in triplicate groups, in a recirculating system. Water temperature and oxygen level were kept constant at 27 1and 100% of saturation, respectively. Five experimental isoproteic diets with increasing lipid level (16%, 18%, 20%, 22% and 24% lipid level, corresponding to D16, D18, D20, D22 and D24, respectively) were administered to satiation twice a day, over 89 days. Data were analyzed using one-way ANOVA and Tukeys post test (P 0.05). The specific growth rate (SGR) didnt show any significant difference between treatments even though feed intake (FI) of fish fed D16 was significantly higher as compared to other treatments. At the same time, the feed conversion ratio (FCR) was higher in fish fed the diet with the lowest lipid level. Whole-body composition, viscerosomatic, hepatosomatic and visceral fat index were not influenced by dietary treatments. Protein efficiency ratio (PER) was significantly lower in D16 (1.44) than in the other treatments (1.55, 1.58, 1.57, 1.56). Gross protein efficiency (GPE) was significantly lower in D16 (24.9) as compared to fish fed D20, D22 and D24 (27.3, 27.3, 26.7). The two lowest dietary lipid levels gave a higher gross lipid efficiency (GLE) (69.9, 69.7) in comparison to the other groups (56.6, 56.0, 49.8). The energy levels studied seem not to influence growth at high temperatures despite the wide range of fat inclusion used. However, low energy diets show higher FCR and lower PER. These findings should be further evaluated.