不同罗非鱼品系感染无乳链球菌后对血液和肝胰腺生化指标的影响

Effects of Streptococcus agalactiae Infection on Blood and Hepatopancreatic Tissue Biochemical Indices in Different Species of Tilapia

为探究无乳链球菌(Streptococcusagalactiae)感染后对罗非鱼的血液和肝胰腺生化指标的影响,本研究以吉富罗非鱼(Oreochromis niloticus)抗病选育系F5代、奥尼罗非鱼(Oreochromis aureus×O. niloticus)、吉富罗非鱼"百桂"品系为对象,通过人工腹腔注射感染无乳链球菌,检测感染后不同时期肝胰腺和血液中的酸性磷酸酶(ACP)、碱性磷酸酶(AKP)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、总抗氧化能力(T-AOC)和溶菌酶(LZM)活性的变化。结果显示,奥尼罗非鱼、吉富罗非鱼抗病选育系F5代和吉富罗非鱼"百桂"品系的平均死亡率分别为55.4%、60.5%和78.6%,表明奥尼罗非鱼抗感染能力最强;3个品系感染无乳链球菌后,肝胰腺组织中的ACP、AKP、SOD和T-AOC酶活力均呈先升高后下降的趋势,其中,在感染后24 h,奥尼罗非鱼的AKP和CAT酶活力显著高于吉富罗非鱼抗病选育系F5代和吉富罗非鱼"百桂"品系;而感染后24 h,血清中ACP、AKP、LZM、CAT和T-AOC酶均显著升高,而SOD酶则下降,其中,奥尼罗非鱼的ACP、AKP、CAT和T-AOC酶活性明显高于吉富罗非鱼抗病选育系F5代和吉富罗非鱼"百桂"品系。综合比较6种酶在感染后不同时期的活性变化及3个品系的感染存活率,筛选出AKP和CAT作为评估罗非鱼抗无乳链球菌感染能力强弱的指标。

Nonspecific immunity plays a vital role in pathogen infection in fish.The bacterium Streptococcus agalactiae is an important pathogen in tilapia cultivation,but its effects on tilapia blood and hepatopancreatic biochemical indices are unclear.We injected three strains of Nile tilapia(Oreochromis niloticus)-a disease-resistant genetically improved farmed tilapia(GIFT)strain,a GIFT Baigui strain,and hybrid tilapia(O.aureus×O.niloticus)-with S.agalactiae,then monitored superoxide dismutase(SOD),catalase(CAT),acid phosphatase(ACP),phosphatase(AKP),lysozyme(LZM),and total antioxidant capacity(T-AOC)enzyme activities in blood and hepatopancreatic tissues.Mortality rates in the hybrid tilapia,GIFT disease-resistant strain,and GIFT Baigui strain were 55.4%,60.5%,and 78.6%,respectively.Post-infection,enzyme activities of ACP,AKP,SOD,and T-AOC in hepatopancreatic tissues of all strains changed,first increasing then decreasing,and AKP and CAT activities after 24 h of infection were significantly higher in the hybrid tilapia than in the two GIFT strains.ACP,AKP,LZM,CAT and T-AOC enzyme activities in blood increased after infection,but SOD activity decreased;ACP,AKP,CAT and T-AOC activities in the hybrid strain were significantly higher than in the two GIFT strains.Using activity changes of the six enzymes and infection mortality rates,we identified AKP and CAT as potential indicators of streptococcal resistance in strains of tilapia.