饲料中DHA含量对中华绒螯蟹幼蟹生长、脂类组成和低氧胁迫的影响

二十二碳六烯酸（C22:6n-3，DHA）对甲壳动物生长、蜕壳、性腺发育、免疫保护和抗环境胁迫具有重要的调节作用，探讨饲料中脂肪酸营养与中华绒螯蟹幼蟹生长和耐低氧胁迫的调控关系具有重要的理论意义和现实意义。通过单个体养殖试验、生化分析、低氧胁迫及生理指标测定等方法，研究了饲料中DHA含量对中华绒螯蟹幼蟹（初始均重为0.6g左右）成活、生长、脂类组成和低氧胁迫下生理指标的影响，探讨幼蟹饲料中适宜的DHA含量。结果表明:（1）饲料中DHA含量对中华绒螯蟹幼蟹的成活、生长、蜕壳和肝胰腺指数无显著影响；（2）饲料中DHA含量对幼蟹肝胰腺水分、肌肉水分及总脂含量均无显著影响，但饲料中过量DHA（0.81%）导致幼蟹肝胰腺总脂含量显著升高；（3）幼蟹肝胰腺和肌肉中的DHA均随着饲料中DHA含量升高而显著上升，但DHA相对保留率（组织中DHA与饲料中DHA的比值）随着饲料中DHA含量上升而显著下降，整体上肌肉中各PUFA的相对保留率远高于肝胰腺。无论饲料中DHA/EPA比值如何变化，肌肉中DHA/EPA均小于1，这说明幼蟹肌肉需要更多的EPA；（4）饲料中添加适量的DHA（0.18%0.28%）可以提高低氧胁迫下幼蟹血淋巴中超氧化物歧化酶的活性，降低其乳酸和丙二醛含量，从而提高幼蟹的抗低氧胁迫能力。综上，中华绒螯蟹幼蟹饲料中适宜DHA含量为0.2%左右。  

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.