四个罗非鱼选育品种抗链球菌病能力差异研究

为筛选出抗病力优良的罗非鱼品种, 以奥利亚罗非鱼“夏奥1号”、尼罗罗非鱼“99”埃及品系、吉富罗非鱼“中威1号”和奥尼罗非鱼为研究对象, 33℃水温暂养7d后分别进行无乳链球菌人工感染实验, 连续7d统计累计死亡率, 并于人工感染后0、24h、48h和72h采集血液和组织样本, 研究这4个罗非鱼选育品种抗链球菌病能力的差异。结果显示: 感染7d后奥尼罗非鱼的累计死亡率最低; 奥尼罗非鱼的谷草转氨酶(AST)感染前后始终都低于其余3个品种罗非鱼(P<0.05); 埃及尼罗和奥尼在感染72h后球蛋白(GLO)分别显著升高1.13倍和1.41倍; 奥尼罗非鱼白蛋白/球蛋白(A/G)在感染前后没有显著性变化(P>0.05), 而其余3个品种罗非鱼A/G比值在感染后都显著性降低(P<0.05); 埃及尼罗的碱性磷酸酶(AKP)在感染72h后显著降低(P<0.05), 奥利亚和吉富的AKP表现为先上升后下降, 奥尼的AKP感染前后没有显著性变化(P>0.05); 各品种罗非鱼血清中的乳酸脱氢酶(LDH)感染后都显著升高(P<0.05); 奥利亚、吉富和奥尼罗非鱼的超氧化歧化酶(SOD)感染48h时都显著升高(P<0.05); 奥尼罗非鱼在感染前后溶菌酶(LZM)活性都显著高于其余3个品种罗非鱼(P<0.05)。组织病理学结果显示:吉富和奥尼肝细胞水肿变性, 而奥利亚和埃及尼罗出现大面积肝细胞脂肪变性; 每个品种罗非鱼均呈现严重的脾炎, 奥利亚、埃及尼罗和吉富的脾脏中大量铁血黄素沉积; 每种罗非鱼呈现不同程度的肾小球萎缩, 肾小管上皮细胞变性、坏死。研究表明奥尼罗非鱼抗链球菌病能力最强, 感染后血清中AST水平与肝受损程度呈一定的正相关, LZM水平和罗非鱼抗链球菌病能力呈一定的正相关。

STUDY ON RESISTANT DIFFERENCE AMONG FOUR BLEEDING SPECIES OF TILAPIA OREOCHROMIS SPP. FOLLOWING STREPTOCOCCUS AGALACTIAE CHALLENGE

The aim of this paper was to identify a tilapia strain that is the most resistant to the infection of Streptococcus agalactiae. The serum biochemical parameters and histopathology of Blue tilapia (Oreochromis aureus) " Xia’ao No.1”, Nile tilapia (Oreochromis niloticus) " 99 strain”, GIFT tilapia (Oreochromis niloticus♀×Oreochromis niloticus♂) " Zhongwei No.1”, Hybrid tilapia (Oreochromis niloticus♀×Oreochromis aureus♂) infected by S. agalactiae were investigated. They were cultured on (33±1) ℃. All fish were acclimated to the laboratory conditions for one week then artificially inducedS. agalactiae to the fish. The cumulative mortality was recorded at different time points. Blood and tissue samples were collected at 0, 12h, 24h, 48h and 72h after infection. The result showed that the cumulative mortality of Hybrid tilapia was significantly lower than that of other species; Glutamic-oxaloacetic transamnase (AST) activity of Hybrid tilapia was consistently lower than that of other three strains (P<0.05); compared with initial measurement, globulin of Nile tilapia and Hybrid tilapia increased by 1.13 times and 1.41 times respectively at 72h after infection. Albumin/globulin (A/G) index of Hybrid tilapia showed no significantly difference (P>0.05), while that of other three species was significantly lower after infection (P<0.05); Alkaline phosphatase (AKP) activity of Nile tilapia decreased significantly at 72h after infection (P<0.05) while AKP levels of Blue tilapia and GIFT tilapia increased first followed by decrease, and AKP of Hybrid tilapia showed no significantly difference (P＞0.05). Lactic dehydrogenase (LDH) of all four strains increased significantly on the progress of disease after infection (P<0.05). Superoxide dismutase (SOD) activities of Blue tilapia, GIFT tilapia and Hybrid tilapia increased significantly at 48h after infection (P<0.05). Lysozyme (LZM) activities of Hybrid tilapia were consistently higher than that of other three strains (P<0.05). Hepatocytes of GIFT and Hybrid tilapia showed hydropic degeneration, while hepatocytes of Blue tilapia, Nile tilapia showed highly vacuolation and macrovesicular steatosis. The spleen of all challenged strains showed had serious splenitis while the spleen of Blue tilapia, Nile tilapia and GIFT tilapia contained a large number of hemosiderin deposition. Renal glomerular atrophy, degeneration and necrosis in renal tubule epithelial cell were apparent after infection. The results indicated that Hybrid tilapia was the most resistant toS. agalactiae; AST in serum was correlated positively with liver damage; LZM level was correlated positively with the anti-Streptococcus ability.