Influence of conjugated linoleic acid on growth, lipid composition and hepatic lipogenesis in juvenile European sea bass (Dicentrarchus labrax)

Dietary conjugated linoleic acids (CLA) can be successfully incorporated in several fish species but have not been evaluated in marine fish. A 12-week growth trial was conducted with European sea bass juveniles, having an initial weight of 13.96 ± 0.16 g (S.D.). Fish were fed to satiation, twice a day, with diets containing graded amounts of CLA (0, 0.5, 0.75, 1.0 or 2%). At the end of the experiment, the daily growth index, feed intake, feed efficiency and whole body composition and tissue fatty acid profile were determined. The activity of some enzymes (glucose-6-phosphate dehydrogenase, G6PD, malic enzyme, ME, and fatty acid synthetase, FAS,) was also measured in the liver. Digestibility of the diets was determined, using chromic oxide as inert tracer, and the Guelph System for faecal collection. No significant differences were detected (P > 0.05) in growth parameters, feed conversion, body composition or nutrient retention among treatments. Dietary CLA did not affect significantly the activity of the lipogenic enzymes when expressed as mIU/mg protein, but when the HSI variations were taken into consideration (IU/100 g fish) the activities of both G6PD and ME seemed to be depressed in fish fed increasing CLA levels. Dietary inclusion of CLA had no effect on tissue lipid content, but significantly affected the total percentages of polyunsaturated (PUFA) and monounsaturated fatty acids (MUFA) in both muscle and liver tissues. Dietary CLA supplementation resulted in a significant increase of the biologically active trans-10, cis-12 and cis-9, trans-11 CLA isomers in both tissues. The total accumulation of CLA was clearly higher in muscle than in liver, reaching 5.61% and 3.00% of total lipids, respectively, in fish fed 2% CLA. The results obtained in this experiment clearly suggest European sea bass can successfully incorporate CLA in both liver and muscle up to 2%, contributing to the production of a functional food.