Effects of dietary n-3 HUFA on growth performance and lipid metabolism in juvenile black sea bream, Sparus macrocephalus.

Abstract

Six diets containing graded levels(0.79,0.83,0.85,0.88,0.92 and 0.94%) of n-3 highly unsaturated fatty acids(n-3 HUFA) with a constant DHA/EPA,were fed randomly to six groups(Diet 1-6) of fish with triplicate [average weight,(8.08±0.09) g;20 fish/replicate] to determine the effects of dietary n-3 HUFA on growth and lipid metabolism in juvenile black sea bream(Sparus macrocephalus).Results of the 8-week growth trial showed that:(1) Hepotasomatic index(HSI) and intraperitoneal fat(IPF) ratio of juvenile black sea bream decreased with the increase of dietary n-3 HUFA and the values in Diet 5 and 6 were significantly lower than those in other four groups(P0.05).Adipocyte diameter in IPF was decreased by dietary n-3 HUFA and the significance occurred between Diet 3 and 6.Lipid content in muscle was significantly affected by dietary n-3 HUFA and reached the bottom in Diet 4.No significance was found in whole body proximate composition of juvenile black sea bream.Concerning the fatty acid composition,∑SFA and the main constituent,C16:0 were negatively correlated with dietary n-3 HUFA,while ∑n-3 HUFA content was obviously increased among all the treatments.DHA to EPA ratios(DHA/EPA) in liver,dorsal muscle and IPF were unchanged with the supplementation of dietary n-3 HUFA.Quadratic analysis based on weight gain rate(WGR) indicated that dietary n-3 HUFA requirement for black sea bream was 0.87% DM.(2) Determination of fatty acid synthase(FAS) and hormone-sensitive lipase(HSL) activities showed that FAS activity kept constant in Diet 1 to 4,and then decreased significantly with further increment of dietary n-3 HUFA.HSL activity in IPF increased significantly with the elevation of dietary n-3 HUFA level and increased to almost two times in Diet 6(0.94% n-3HUFA).Gene expression of FAS changed following the similar trend with FAS activity in liver;while expression of HSL in IPF was positively correlated with dietary n-3 HUFA level.In summary,we can deduce that n-3 HUFA regulation in lipid metabolism was realized by affecting the lipogenesis and lipolysis at the same time.