Growth response of juvenile dentex (Dentex dentex, L.) to varying protein level and protein to lipid in practical diets

The dentex (Dentex dentex L.) is a fast-growing sparid which represents a possible candidate for Mediterranean mariculture. As the basic nutrient requirements of this species are unknown, two feeding trials were carried out to identify suitable protein and lipid (energy) levels to be used in formulating practical diets for dentex. The experiments used groups of 30 specimens (each fish weighing 17 or 20.7 g) which were kept in 12 flow-through 160 1 tanks supplied with seawater at 21 min(-1) (temperature 20 +/- 1 degrees C; salinity 33 ppt). An initial 4-week trial was conducted to obtain a preliminary estimate of the optimal protein level. Triplicate groups were fed four practical diets with increasing levels of protein (44.3, 49.3, 55.7 and 58.9% dry matter (DM), over 90% of which was supplied by white fish meal) and a constant lipid content (17.3% DM; mostly supplied by fish lipids) to satiation. An analysis of the nutrient-weight gain relationship indicated that the optimal dietary protein level was 49.3% DM. In a second 60 day experiment, duplicate groups of fish were fed six diets with three protein levels (44.4, 49.5 and 55.8% DM) and two lipid contents (12.0 and 17.3% DM) within each protein level, nearly to satiation. Growth performance was lowest in fish given diets containing 44.4 or 49.5% protein and 12% lipid and was improved (P < 0.05) either with diets supplying 55.8% protein (regardless of dietary lipid)or 49.3% protein and 17.4% lipid. The results observed in the second trial suggest that when protein efficiency or retention are considered even dietary levels of 44.3% protein and 17.2% lipid (i.e. 24.3 g protein kJ(-1) calculated available energy) could be assumed as suitable levels for formulating practical diets for this species, providing high quality fish meal and oil are used.