Effects of dietary arachidonic acid (20:4 n-6), on growth, body composition, and tissue fatty acid profile of gilthead bream fingerlings ( Sparus aurata L.)

Abstract

The effect of feeding gilthead sea bream fingerlings diets supplemented either with increasing amounts of arachidonic acid (ArA, 20:4 n-6) or high n-3 highly unsaturated fatty acid (HUFA) levels on gilthead bream performance and fatty acid composition was studied. Fish of an initial weight of 1.4 g were grown to a final average weight of 18.5 g at a temperature of 25 °C. The diets used contained fish meal LT and gelatinized corn starch as main ingredients. Additional oil to a final content of 15% of the diet was supplied either by olive oil (OO), ArA content about 0.2% of total fatty acids (FA) (diet A0), or mixtures of OO and an ArA-rich oil to formulate three diets, A1, A2 and A3 with increasing levels of ArA (3.9%, 7.6% and 11.2% of total FA), or a docosaexaenoic (DHA, 22:6 n-3)-rich oil to attain a dietary DHA+EPA (eicosapentaenoic, 20:5 n-3) content of about 4% of the diet (diet D ArA content, 1.1% of FA). The DHA+EPA content of all other diets was 2% of the diet. No differences were found among experimental groups on growth, nutrient utilization efficiencies or whole body and liver composition. A tendency for reduced lipid levels was however apparent in ArA-supplemented diets for muscle, gill and liver tissue. Tissues examined for their fatty acid profile were liver, muscle, gills, and intestine. ArA was more concentrated in polar (PL) than in neutral lipids (NL) of all tissues studied. A strong correlation appeared to exist ( P<0.01) between dietary and PL levels of ArA in all tissues studied. Ratios of deposition to dietary level were higher at low dietary ArA especially for gill tissue and decreased at higher ArA concentrations between 2% and 3% of the total FA. Ratios for muscle approached a value of 2, while a ratio of 1 was approached for all other tissues. An increase of ArA levels in tissue PL decreased levels of EPA. Comparison of fatty acid compositions of tissue PL of the tissues studied to those measured previously in respective tissues of wild bream indicated that dietary ArA concentrations between 3.9% and 7.6% of total FA approached more closely the composition of wild fish.