EFFECTS OF DIETARY DHA LEVELS ON GROWTH, LIPID COMPOSITION AND HYPOXIA STRESS OF JUVENILE CHINESE MITTEN CRAB ERIOCHEIR SINENSIS

Docosahexaenoic acid (C22: 6n-3, DHA) is one of the important highly unsaturated fatty acids (HUFAs) for the regulation of growth, molting, gonadal development, immunity and environmental stress resistance of crustacean. We investigated the effects of dietary DHA levels on survival, growth, molting period, lipid composition and hypoxia stress of juvenile Eriocheir sinensis. Five experimental diets were formulated containing 0.06%, 0.18%, 0.28%, 0.55% and 0.81% of DHA. Each diet was randomly assigned to triplicate groups of juvenile crabs with initial body weight around 0.6g, and each group contained 20 individually cultured crabs. The results showed that, (1) Dietary DHA had no significant effect on survival, growth, molting period and hepatosomatic index for juvenile E. sinensis; (2) excessive diet DHA (Diet 5, DHA=0.81% dry weight) led to significantly higher lipid contents in the hepatopancrea. Despite hepatopancrea or muscle, the tissue DHA percentage was significantly increased with the increase of dietary DHA levels. However, the relative retention ratio (tissue particular fatty acid percentage/dietary respective fatty aid percentage) of tissue DHA deceased dramatically from Diet 1 to Diet 5 treatment; (3) despite of dietary DHA/EPA ratio, the DHA/EPA ratio of muscle remained less than one, which indicated crab muscle required less DHA than EPA; (4) among eight physiological indices of juvenile E. sinensis under hypoxia stress, malondialdehyde (MDA), lactic acid (LA) and superoxide dismutase (SOD) were good indicators for the evaluation of crab hypoxia stress resistance. The optimal dietary DHA content (Diet 2 and Diet 3) led to lower MDA and LA levels and higher SOD activity than the Diet 1 without DHA supplementation did. In conclusion, our results indicated the optimal dietary DHA level was around 0.2% of dry diet or 3% of total fatty acids.