我国淡水养殖动物主要致病性水霉菌病原的分析

应用ITS(internal transcribed spacer,ITS)区分子系统发育进化分析法和限制性片段长度多态性分析法(Restriction Fragment Length Polymorphism,RFLP)相结合,对近年来分别采集于中国上海、江苏、江西、四川、河北、浙江、湖北等7个主要淡水养殖区的60株疑似致病性水霉菌(Saprolegnia)进行鉴定分类,并系统分析了我国已报道的致病性水霉菌的分类情况,比较了分别分离自鱼体和卵的多子水霉的生物学特性。研究结果表明,60株疑似水霉菌分为10个基因型,其ITSLPCR-LRFLP谱型一致属于典型多子水霉(Saprolegniales ferax)、寄生水霉(Saprolegniales parasitia)和澳大利亚水霉(S.australis)分组类型;ITS系统发育进化分析结果显示,我国致病性水霉菌以多子水霉和寄生水霉为主,二者为我国淡水养殖主要的致病性水霉菌病原。此外,对鱼体和卵来源的多子水霉生物学特征进行比对后发现,二者没有明显差异,同一致病菌株既可感染鱼体也可感染卵。此研究的开展丰富了我国致病性水霉菌分类统计的生物学资料,为水霉病预警和药物防治技术的开发提供了重要的参考价值。

Identification of major pathogenic Saprolegnia species in freshwater aquaculture of China

This study used Restriction Fragment Length Polymorphism (RFLP) and Internal Transcribed Spacer (ITS) PCR sequencing technology to identify 60 isolates of suspected pathogenic Saprolegnia strains collected from 7 provinces including Shanghai, Jiangsu, Jiangxi, Sichuan, Hebei, Zhejiang and Hubei. Taxonomical analysis was also performed with strains of Saprolegnia reported in recent years. Comparative studies of physiological and molecular characteristics of pathogenic strains isolated from both infected fishes and eggs were carried out. The results showed that the 60 isolates could be classified into 10 special genetypes and all the isolates belonged to the clade of S. ferax, S. australis and S. parasitia by ITS-RFLP. Based on the phylogenetic tree, S. ferax and S. parasitia were the main Chinese pathogenic Saprolegnia strains. In addition, no significant difference existed in morphology of both asexual and sexual organs between the two S.ferax isolates from infected fishes and eggs. The same isolate could infect amphibian eggs and fishes. Thus, S.ferax and S.parasitia were identified as major pathogenic strains for both fish and eggs. The results could serve as a reference for the control of Saprolegniasis.