Effect of dietary non-protein energy levels on condition and oxidative status of Senegalese sole (Solea senegalensis) juveniles

The effects of dietary non-protein energy levels on growth, oxidative status and condition were studied in juveniles of Senegalese sole (Solea senegalensis). Four isonitrogenous diets with four energy levels were used: A--low (11% lipid, raw carbohydrate); B--intermediate (11% lipid, digestible carbohydrate); C--intermediate (21% lipid, raw carbohydrate); and D--high (21% lipid, digestible carbohydrate). Survival, relative growth rate (RGR) and feed conversion rate were not significantly affected by the dietary treatments. The fatty acid composition of the fish muscle varied little among the treatments, but trans 18:2n-6, total n-6 and EPA/DHA ratio, tended to be higher in fish fed diets with low lipid level. Cellular energy allocation (CEA) results (indicative of metabolic status and net energy budgets) showed significant differences in liver, but not in muscle samples. Livers of fish fed diet C contained the lowest carbohydrate, protein and CEA values, but the highest cellular energy consumption. Fish fed diet A had the highest CEA for growth, followed by fish fed diets B and D and then diet C. The liver and muscle peroxidation and antioxidant activity were measured by thiobarbituric acid reactive substances (TBARS) test and the enzymatic activities levels of catalase (CAT) and superoxide dismutase (SOD). TBARS values were higher for fish fed diets with high lipid content. However, no clear relation was found between HUFA level and TBARS value. The activity levels of the antioxidant enzymes CAT and SOD were higher in livers of fish fed diets with a high lipid level. Furthermore, CAT and SOD activity and TBARS values were influenced by the type of dietary starch in the diet. Higher oxidation rates were observed in fish fed diets containing raw carbohydrate. These data suggest that lipid and carbohydrate energy sources affect the oxidative status of Senegalese sole. Diets containing low levels of lipid and digestible starch reduce the susceptibility of the fish to oxidation and may enhance growth rate.