Effect of dietary carbohydrate-to-lipid ratios on growth, lipid deposition and metabolic hepatic enzymes in juvenile Senegalese sole (Solea senegalensis, Kaup)

A study was undertaken to determine the effect of various dietary carbohydrate-to-lipid ratios on growth performance, whole-body composition and tissue lipid content in Senegalese sole (Solea senegalensis) juveniles. Data on the dietary regulation of key hepatic enzymes of the lipogenic and glycolytic pathways glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME; fatty acid synthetase, FAS; pyruvate kinase, PK and glucokinase, GK) were also generated. Four isonitrogenous (crude protein: 52% dry matter (DM)) diets were formulated to contain one of two lipid levels (11% and 21% DM). Within each dietary lipid level, the nature of the carbohydrate fraction (raw or extruded peas) was varied. Triplicate groups of 54 sole (initial body weight: 23.6+/-1.2 g) were grown in recirculated seawater over 67 days. Fish were fed using automated feeders. At the end of the study, whole-body, liver, viscera and muscle samples were withdrawn for analyses. During the experimental period, the mean fish weight about doubled in all treatments. No significant differences were found in growth performance (ranging from 1.1% to 1.4% body weight day-1) among dietary treatments. High-fat diets increased whole-body fat content. Similarly, daily fat gain ranged from 0.54 to 0.78 g kg-1 day-1 and highest values were found in fish fed high-lipid diets. Dietary treatments also affected tissue lipid content (liver, viscera and muscle), with highest values in fish fed high-fat diets. The nature of dietary carbohydrates had little influence on performance criteria, but affected tissue lipid deposition. The activities of G6PD, ME and FAS were depressed by elevated levels of dietary lipid, confirming the inhibitory effect of dietary fats on lipid biosynthesis. At both dietary lipid levels, ME and FAS activities were little affected by dietary carbohydrate. Activities of PK and GK were not affected by the starch level of the diets. In Senegalese sole juveniles, the lipogenic pathway is more susceptible to modulation by dietary means (particularly through lipid intake) than the glycolytic pathway.