This study was designed to investigate the effects of dietary lysozyme supplementation on serum biochemical indices,antibacterial properties and liver antioxidant capacity of GIFT tilapia (Oreochromis niloticus) under ammonia-nitrogen stress.Juvenile tilapia with the initial weight of (11.35±0.08) g were fed with six experimental diets (labeled as L0,L18,L36,L54,L72 and L90) which were supplemented with graded lysozyme levels (0,18,36,54,72 and 90 mg/kg) in basal diet for 60 days.After that,a 24 h ammonia-nitrogen stress test with ammonia chloride was conducted to the experimental fish above.The results showed that:① After stress,fish serum biochemical indices presented a significant difference and the fish showed different feedback responses among groups (P＜0.05).The fish in L54 group could reduce damage from ammonia-nitrogen stress through stimulating the immune system and regulating protein metabolism;while mainly through regulating the dynamic variation between high/low density lipoprotein cholesterol,cholesterol and triglyceride in L72 and L90 groups.② Serum antibacterial test showed that there was the maximum resistance ability to Escherichia coli,Staphylococcus aureus,Aeromonas hydrophila in L54 and L72 groups and higher inhibiting ability to Vibrio alginolyticus in L36～L90 groups (P＜0.05),while lysozyme supplementation was helpful for the proliferation of Bacillus subtilis (P＜0.05).③ Liver superoxide dismutase,catalase and glutathione peroxidase activity after ammonia-nitrogen stress were generally enhanced with increased dietary lysozyme level and the highest value was presented in L54 group (P＜0.05);Malonaldehyde content in each lysozyme supplemented group was significantly lower than the control group (P＜0.05).In summary,our results indicate that ingestion of a basal diet supplemented with 54 and 72 mg/kg lysozyme could produce a most positive and effective regulatory response on serum biochemical indices,antibacterial properties and liver antioxidant indices under ammonia-nitrogen stress,so as to improve fish anti-stress ability.%为研究氨氮应激下溶菌酶对吉富罗非鱼血清生化指标、抗菌性能及肝脏抗氧化能力的影响,用6种不同溶菌酶添加水平(0、18、36、54、72和90 mg/kg)的饲料(分别记为L0、L18、L36、L54、L72和L90)饲喂初始均重为(11.35±0.08)g的罗非鱼60 d,之后应用氯化铵进行24 h氨氮应激实验.结果显示:①应激后,各组鱼的血清生化指标在组间存在较大差异(P＜0.05),不同溶菌酶添加水平下的鱼体对氨氮应激产生了不同的响应机制.L54组鱼主要通过激发免疫系统并调节蛋白质代谢来抵抗氨氮浓度突变;L72和L90组鱼主要通过调节高密度脂蛋白和低密度脂蛋白、胆固醇和甘油三酯之间的动态变化来缓解氨氮对机体的应激.②血清抗菌实验表明,L54和L72组鱼对大肠杆菌、金黄色葡萄球菌和嗜水气单胞菌的抑制能力最大,且显著高于对照组(P＜0.05);L36～L90组对溶藻弧菌的抑制作用显著高于对照组和L18组(P＜0.05);各溶菌酶添加组的鱼对枯草芽孢杆菌具有不同程度的保护作用.③应激后肝脏的超氧化物歧化酶、谷胱甘肽过氧化物酶和过氧化氢酶活性随溶菌酶添加水平的增加总体呈现先升后降的变化趋势,L54组显著高于对照组(P＜0.05);各添加组丙二醛含量均显著低于对照组(P＜0.05).研究表明,54和72mg/kg溶菌酶添加水平对氨氮应激下吉富罗非鱼的血清生化指标、抗菌活性和肝脏抗氧化指标产生了最积极有效的调控,能够增强鱼体的抗应激能力.
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