中文摘要：

采用中心复合试验设计（CCD）和响应曲面方法（response surface methodology,RSM）,探讨了氨氮（0.02～2.00 mg/L）和养殖密度（1～5尾/10 L）对吉富罗非鱼幼鱼生长和肝脏抗氧化指标的联合影响。结果表明,本试验条件下,氨氮和养殖密度的一次与二次效应对特定生长率有显著影响（P〈0.05）,随着氨氮或养殖密度的上升,特定生长率呈先上升后下降的变化。氨氮与养殖密度之间存在互作效应（P〈0.05）,氨氮浓度为0.02～0.20 mg/L,养殖密度在1～2尾/10 L时,幼鱼特定生长率较高;而氨氮浓度高于0.20 mg/L,养殖密度在3尾/10 L左右时,生长速度较快。肝脏丙二醛（MDA）含量随氨氮浓度和养殖密度的上升而上升,超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的活力呈先上升后下降的变化。氨氮与养殖密度的一次效应对MDA含量和两种酶活力均有显著影响（P〈0.05）,二次效应对两种酶活力的表达有极显著影响（P〈0.01）;氨氮与养殖密度对CAT活力有互作效应,高浓度氨氮与高养殖密度环境会抑制SOD和CAT活力的表达。因子与响应值间二次多项回归方程的决定系数分别达到0.972 4、0.913 2、0.938 9和0.969 2（P〈0.01）,可用于预测;氨氮效应对生长和抗氧化酶活力的影响较养殖密度明显。建议在罗非鱼的养殖过程中合理安排好养殖密度,保持溶氧充足,降低氨氮胁迫,提高罗非鱼的生长与抗病力。

英文摘要：

Response surface methodology（RSM）and Central Composite Rotatable Design（CCD）were used to study the combined effects of ammonia（0.02-2.00 mg/L）and density（1-5 ind/10 L）on the specific growth rate（SGR）and antioxidant activities in the liver of juvenile tilapia（Oreochromis niloticus）.The objectives were to find out the linear,quadratic or reciprocal effects of ammonia and density on the growth and antioxidant activities in the liver of juvenile tilapia by the regression equation.The results showed that the linear and quadratic effects of ammonia and density on the SGR were significant（P〈0.05）,SGR increased at the beginning and then decreased with the increased concentrations of the ammonia,and the density effects showed the same trend.There was a significant interactive effect between ammonia and density on growth（P〈0.05）.Higher SGR was observed when the density was 1-2 ind/10 L and ammonia was 0.02-0.20 mg/L.When concentrations of external ammonia were higher than 0.2 mg/L and density were around 3 indiv/10 L,SGR was also higher.With the increased concentrations of ammonia and density,the content of MDA in the liver increased gradually,while the activities of SOD and CAT increased at the beginning and then decreased.The linear effect of ammonia and density had significant effects on MDA,SOD and CAT（P〈0.05）,the quadratic effects of ammonia and density had very significant effects on the SOD and CAT（P〈0.01）.There was a significant interactive effect between ammonia and density on CAT activity.High concentrations of external ammonia and high density inhibited SOD and CAT activities.Model equations of the effects of ammonia and density on SGR,MDA,SOD and CAT were established,with the R2 being 0.972 4,0.913 2,0.938 9 and 0.969 2 respectively（P〈0.01）,which could be used for prediction.Growth and activities of antioxidant enzymes were more influenced by ammonia than by density.In the cultural practice,it is suggested that the density should be controlled reasonably and