High dietary lipid levels enhance digestive tract maturation and improve Dicentrarchus labrax larval development

This study was designed to determine the nutritional lipid requirement of seabass larvae and to understand the effects of dietary fat concentration on their digestive tract maturation. Seabass (Dicentrarchus labrax) larvae were fed, from d 15 to 38 of life, one of five isonitrogenous compound diets with different lipid levels, ranging from 10 to 30 g/100 g, The higher the lipid level, the greater the growth and survival of the larvae (P < 0.05). The lipolytic enzymes assayed, lipase and phospholipase A(2), were stimulated by the increase in their respective dietary substrates, triglycerides and phospholipids, in 38-d-old larvae (P < 0.05). Nevertheless, a plateau in the activity of these two lipolytic enzymes was observed from 20% dietary lipids onwards, The similar mRNA revels of phospholipase A(2) in the three groups fed the highest lipid levers suggested that the maximal synthesis level of lipolytic enzyme was reached at 20% dietary fat, Pancreatic secretion of trypsin and amylase were positively affected by the dietary lipid level; a possible involvement of a cholecystokinin-releasing factor is discussed. Diets containing >20% lipids led to the increase in activities of brush border membrane enzymes to the detriment of a cytosolic enzyme in enterocytes, leucine-alanine (Leu-Ala) peptidase, This enzymatic change reveals the earlier maturation of enterocytes in larva groups fed high lipid levels.