中文摘要：

以吉富罗非鱼、新吉富罗非鱼、埃及尼罗罗非鱼和红罗非鱼为研究对象,饲养100d后,进行海豚链球菌（2.95×108CFU/mL）感染试验,分析攻毒前后各品系罗非鱼的血液生化指标和肝脏HSP70 mRNA表达量的变化规律。另从各桶中取20尾鱼进行同样的攻毒试验,统计攻毒后各时间点的累积死亡率。结果表明,感染海豚链球菌96h后,吉富罗非鱼和新吉富罗非鱼对病原较为敏感,累积死亡率分别达到36.67%和38.33%;埃及尼罗罗非鱼对病原敏感性较差,试验期间未见死亡。吉富罗非鱼、新吉富罗非鱼和红罗非鱼血清皮质醇和葡萄糖水平以及肝脏HSP70 mRNA的表达量在攻毒后明显提高,血清谷丙转氨酶、谷草转氨酶与溶菌酶活力也呈上升趋势,碱性磷酸酶活力与甘油三酯和胆固醇水平低于攻毒前。埃及尼罗罗非鱼可以利用糖原和脂类产生的能量,提高了HSPS与一些特定免疫蛋白（溶菌酶、球蛋白等）的合成,增强了鱼体的非特异性免疫力。罗非鱼选育过程中,需要将抗病力与生长性能进行有效的结合,在注重生长速度的同时也要增强其抗应激能力,从而为罗非鱼产业的可持续发展提供保证。

英文摘要：

In order to establish the superiority, four different tilapia strains （GIFT tilapia, New GIFT tilapia, Egypt Nile tilapia and Red tilapia） were compared in the study. At day 100 tilapias in the treatment group were intraperitoneally injected with Streptococcus iniae suspension （2.95×108 /mL） to evaluate disease resistance of four different tilapia strains against S. iniae in terms of the serum biochemical parameters and hepatic HSP70 mRNA expression before and after infection. Another set of twenty fish taken from each tank was challenged with S. iniae using the same method as above, and the cumulative mortality of 4 strains was recorded at different times post infection. The results showed that GIFT tilapia and New GIFT tilapia were more sensitive to S. iniae at 96 h after infection, cumulative mortalities were 36.67% and 38.33% respectively. Egypt Nile tilapia was less sensitive to pathogen and no death occurred during the experiment. The levels of serum cortisol （COR） and glucose （GLU） and expression levels of HSP70 mRNA in GIFT tilapia, New GIFT tilapia and Red tilapia strains were highly significant（P0.05）, and the activities of glutamic-pyruvic transaminase （ALT）, glutamic-oxaloacetic transaminase （AST）and lysozyme （LSZ） also increased, while serum alkaline phosphatase （AKP）, triglyceride and cholesterol levels were significantly lower than those prior to infection （P0.05）. By utilizing the energy from resolved hepatin and lipid, the synthesis of hepatic HSP70 mRNA and levels of LSZ and globulin in Egypt Nile tilapia were improved, and thus the non-specific immunity strengthened. It is suggested that in the course of tilapia breeding, effective combination of the disease resistance with growth be conducted so as to guarantee sustainable development of the tilapia industry.