中文摘要：

以初始体质量为（7.27±0.40）g的青鱼为研究对象,采用维生素C（VC）含量分别为0（对照组）、16.3、33.9、69.1、137.8和277.5 mg/kg 6种等氮等能实验饲料,饲养青鱼8周后,选取0、69.1和277.5 mg/kg VC组进行24 h氨氮胁迫（20 mg/L）,研究VC对青鱼幼鱼生长、免疫及抗氨氮胁迫能力的影响。结果显示：以特定生长率为指标,折线模型分析表明青鱼有效维生素C需要量为63.0 mg/kg。肌肉、肝脏和血清中VC积累量与饲料中VC含量呈正相关性,当VC添加量达到137.8 mg/kg时,肌肉和肝脏中VC积累量达到饱和。饲料中添加VC对血清总超氧化物歧化酶（T-SOD）活性及丙二醛（MDA）含量无显著影响,饲料中添加VC显著提高了血清谷胱甘肽过氧化物酶（GSH-px）和过氧化氢酶（CAT）活性（P〈0.05）;血清中谷胱甘肽（GSH）含量和鳃丝Na＋/K＋-ATP酶活力（NKA）随饲料中VC添加量的增加呈升高趋势,而血清皮质醇含量（COR）呈下降趋势。氨氮胁迫有使肝脏和肌肉VC含量、血清T-SOD、CAT、GSH-px活性、GSH含量和鳃丝NKA活性降低,血清VC含量、COR和MDA含量增加趋势。其中,对照组T-SOD、CAT、NKA活性、GSH、MDA和COR胁迫前后差异显著（P〈0.05）,氨氮胁迫使VC添加组青鱼肝脏VC含量显著降低（P〈0.05）,而CAT、NKA活力、GSH、COR胁迫前后均无显著变化。69.1 mg/kg VC组T-SOD活性胁迫前后无显著差异,但GSH-px活性和MDA含量胁迫前后差异显著（P〈0.05）,而277.5 mg/kg VC添加组GSH-px活力和MDA含量胁迫前后差异不显著,但T-SOD活性显著降低,血清VC含量显著升高（P〈0.05）。研究表明,青鱼获得最好生长的饲料有效VC添加量为63.0 mg/kg,氨氮胁迫使青鱼产生免疫应激反应,而补充VC可有效增强机体免疫,缓解机体免疫应激,改善青鱼抗氨氮胁迫能力。

英文摘要：

Studies were conducted to investigate the effects of dietary vitamin C（VC）on growth,immunity and anti-ammonia-nitrite stress ability in juvenile black carp,Mylopharyngodon piceus（initial average weight 7.27±0.40 g）.Six iso-nitrogenous and iso-energetic diets were formulated to supply at dosages of 0（control）,16.3,33.9,69.1,137.8 and 277.5 mg/kg vitamin C diet,respectively.After feeding 8 weeks,according to specific growth rate,three group of 0,69.1 and 277.5 mg/kg of black carp were subjected to an ammonia-nitrite stress（20 mg/L）for 24 h.Results indicated that the effective vitamin C content for maximum growth is about 63.0 mg/kg.The vitamin VC levels in liver,muscle and serum were in positive correlation with VC content in diet,and no significant differences were observed among fish fed the diets with equal to or higher than 137.8 mg/kg of vitamin VC.No significant differences in total superoxide dismutase（T-SOD）and malondialdehyde（MDA）were observed among dietary treatments.But VC could significantly increase the catalase（CAT）and glutathione peroxidase（GSH-px）activity（P0.05）.With the VC content increased,CAT increased at first and then decreased.Glutathione（GSH）and Na＋/K＋-ATPase（NKA）increased when VC concentration in diets were increased,cortisol（COR）were decreased at first and then increased.After ammonia-nitrite stress,each group of the VC concentration in liver,T-SOD,CAT,GSH-px activity and GSH content in serum and gill NKA activity decreased,serum VC level,COR and MDA content increased.The T-SOD,CAT and NKA activity,GSH,MDA and COR content significantly changed before and after ammonia-nitrite stress.Liver vitamin C concentration in fishes fed VC diets significantly decreased after stress,however,there are no significant changes in CAT,NKA activity and GSH,cortisol content compared with control group.T-SOD activity in 69.1 mg/kg vitamin C diet had no significant change before and after stress,but GSH-px activity and MDA content had significantly changed.In