舟山地区大棚凡纳滨对虾生长缓慢病因的调查分析

2013年以来,浙江省舟山地区大棚养殖的凡纳滨对虾(Penaeus vannamei)普遍出现生长缓慢、养殖成功率低的现象。为了查明该原因,本研究采用分子生物学和组织病理学等方法对引起对虾生长缓慢的病因开展了调查分析。结果显示,采集的270份病虾样本中,对虾肝肠胞虫(Enterocytozoon hepatopenaei,EHP)PCR阳性检出率高达85.19%,传染性皮下及造血器官坏死病毒(infectious hypodermal and hematopoietic necrosis virus,IHHNV)检出率为0;所有采集的病虾样本中也未分离到常见的致病菌;54份正常的对虾样本中EHP和IHHNV均未检出。将病虾PCR扩增产物进行序列测定和比对分析,结果获得的序列片段与Gen Bank中已有EHP相关序列相似性高达99.55%;病虾的肝胰腺组织病理切片观察显示,在虾肝胰腺组织中可观察到处于各个生长发育阶段的EHP。通过上述研究,初步认为EHP是引起舟山地区大棚养殖对虾生长缓慢的一个重要病原。

Pathogenicity of Penaeus vannamei slow growth syndrome in intensively cultured penaeid shrimp in Zhoushan

Slow growth of farmed Penaeus vannameihas been reported throughout shrimp growing areas of Zhoushan since 2013, resulting in severe economic losses for high density P. vannamei farmers. Bacterial culture, histopathology, and polymerase chain reaction analyses were conducted to identify the pathogenicity of these slow growing, multiple infections. Infectious hypodermal and hematopoietic necrosis virus (IHHNV) and the micro-sporidian Enterocytozoon hepatopenaei (EHP), which are typical slow-growing pathogens, were analyzed by po-lymerase chain reaction in 270P. vannamei samples collected from high-density, slow-growing Zhoushan shrimp in farm ponds. The results showed a high incidence of EHP (230/270, 85.19%), but no evidence of IHHNV infec-tion. Bacteria were not consistently isolated from the diseased shrimp, and EHP and IHHNV were not detected in any normal appearing shrimp. A BLAST analysis of the sequenced product revealed 99.55% similarity with the matching region of small subunit rRNA from EHP (KF362130). Histopathological sections showed microsporidial spores only in the cytoplasm of hepatopancreatic tubule epithelial cells from diseased shrimp. Based on the ultra-structural features of the family Enterocytozoonidae and the cytoplasmic location of the plasmodia, the pathogen causing slow growth syndrome in Zhoushan was EHP. EHP is a microsporidian parasite that was first isolated and characterized from the giant or black tiger shrimp Penaeus monodon. Although EHP does not appear to cause mortality, shrimp farmers have reported that it is associated with severely retarded growth in P. vannameicom-pared with their unaffected counterparts. No specific signs were observed in shrimp at the early stage of patho-genicity, which differs from the most common microsporidian reported previously from cotton shrimp. Further studies are required to understand the interaction between this host and pathogen.