Physiological and metabolic protein-sparing effects of dietary lipids on common snook Centropomus undecimalis (Bloch, 1792) juveniles

Carnivorous common snook (Centropomus undecimalis) has potential for aquaculture, but its protein requirement in diet is 500 g kg(-1) and the energetic role of lipids in this species has not been explored. Thus, this study investigated the ability of juvenile common snook (8.7 +/- 1.2 g) to use dietary lipids as an energy source. The fish were fed four practical diets with two protein levels (400 and 500 g kg(-1)) associated with two lipid levels (60 and 120 g kg(-1)) for 12 weeks. Growth performance significantly improved with increasing dietary lipid levels, but no significant difference was observed at the protein level. Fish fed the 400:60 (protein: lipid level) diet exhibited significantly higher feed conversion ratios than those fed 400:120, 500:60 and 500:120 diets, but fish fed the 400:120 diet had significantly higher protein efficiency ratios. Juvenile common snook showed the ability to modulate digestive protease and lipase secretion when dietary protein or lipid levels were modified. The activity of alanine aminotransferase decreased as the dietary lipid level increased (p < .05), while fructose-1 and 6-bisphosphatase activities were not significantly affected by dietary protein or lipid levels. Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and pyruvate kinase activities increased as dietary protein and lipid levels increased (p < .05). The results of this study indicate that an increase in dietary lipid level has a protein-sparing effect and that the diet containing 400 g kg(-1) protein with 120 g kg(-1) lipid is suitable for growth and effective protein utilization in common snook.