南方鲇稚鱼爆发性死亡的病原鉴定

Identification of pathogens in an outbreak deaths of southern catfish( Silurus meridionalis) juveniles

2012年7月,四川简阳市某养殖户水泥培育池的南方鲇(Silurus meridionalis)稚鱼发生了爆发性死亡,针对患病南方鲇稚鱼进行了寄生虫学、细菌学及病毒学鉴定。结果显示,病鱼鳃丝压片及体表粘液涂片在光学显微镜下未发现寄生虫。无菌操作分离得到2株优势菌,对其进行了形态学观察、生理生化鉴定、16S rDNA序列分析及系统进化树构建,结果表明,这两株细菌均为维氏气单胞菌(Aeromonas veronii)。动物回归感染试验表明其患病症状同自然发病症状,证明该菌为致病菌。14种常用药物敏感性试验结果显示,病菌对庆大霉素、多粘菌素B和美福仙敏感,对强力霉素、四环素、氟哌酸等10种药物不敏感。对病鱼组织匀浆攻毒试验和疑似病毒PCR检测,结果Ⅱ型疱疹病毒和蛙虹彩病毒特异性引物未能扩增出条带,仅斑点叉尾病毒orf 8引物扩增出157 bp大小的片段,且攻毒试验组鱼全部死亡,对照组鱼未死。因此确定该批爆发性死亡的南方鲇稚鱼感染斑点叉尾病毒。综上所述,此次爆发性死亡的南方鲇稚鱼病原经鉴定为斑点叉尾病毒和维氏气单胞菌。

There was an outbreak deaths of southern catfish（ Silurus meridionalis） juveniles in Jianyang city of Sichuan province on July,2012. The diseased southern catfish juveniles were collected for analysis of the pathogen in parasitology, bacteriology and virology to make the pathologic agent clear. Parasite was not observed under optical microscope in gill and mucus,however,two strains were isolated using routine bacteria separation method. After bacteriological examination, 16S rDNA sequence analysis and the construction of phylogenetic tree,the both two isolates were identified as Aeromonas veronii. The animal regression test results of using the two isolates to infect southern catfish displayed that the prevalence of symptoms and spontaneous onset symptoms were the same. It proved that the isolates were pathogenic to southern catfish. Susceptibility test showed that Aeromonas veronii was sensitive to gentamycin,polymyxin B sulfate,mefoxin. It showed resistance to doxycycline,tetracyclines,norfloxacin and other 10 kinds of drugs. And at the same time,the deaths of southern catfish were confirmed to be channel catfish virus infection by tissue homogenate challenge test and suspected virus PCR detecting technology. The specific primers design for rana grylio virus,herpesvirus type Ⅱ,and channel catfish virus,were applied to the amplification for detecting the possible virus in the diseased fish. The specific ladder product about 157 bp was only amplified with primers designed by channel catfish virus orf 8 gene. All the fish used for tissue homogenate challenge test were dead,the control group fish did not die. As a conclusion,the pathogen of the outbreak deaths of southern catfish juveniles were identified as channel catfish virus and Aeromonas veronii,the research played a significant role indisease prevention and control of southern catfish juveniles.