Protein hydrolysate vs. fish meal in compound diets for 10-day old sea bass Dicentrarchus labrax larvae

Abstract

Four groups of Dicentrarchus labrax larvae were fed from day 10 post-hatching to day 41 with four isoenergetic and isonitrogenous (60%) compound diets differing only by the incorporation level of a commercial fish protein hydrolysate, CPSP G. In diet H0, the protein fraction was fish meal. In diets H19, H38 and H58, 25, 50 and 75% of the fish meal was replaced by CPSP, respectively. The four compound diets sustained larval growth throughout the experiment. The highest survival was obtained in the group fed H19 (47±5.0%). Final weights of larvae fed H0 and H19 diets (5.5±2.61 and 5.7±2.77 mg, respectively) were significantly higher than those of larvae fed diets H38 and H58 (3.3±1.03 and 2.6±0.70 mg, respectively). At day 41, the highest trypsin secretion levels were obtained in groups fed diets H0 and H19, suggesting a proper maturation of pancreatic digestive function. The incorporation of 19 and 38% hydrolysate in diets induced a high level of two membranous enzymes of intestine, alkaline phosphatase (AP) and aminopeptidase N (lap) as early as day 20. The cytosolic enzyme leucine–alanine peptidase (leu–ala) was also assayed. The ratios of AP/leu–ala and lap/leu–ala revealed that the development of the intestine was more advanced in the H19 fed group than in the others. The proper onset of intestinal digestive function was associated with good larvae survival. The experiment showed that the incorporation of a moderate dietary level of fish protein hydrolysate facilitates the onset of the adult mode of digestion in developing fish.