中华绒螯蟹肝胰腺白化症的病因研究

2002年10月以来,通过逐户访问及调查问卷的形式对2001～2002年东太湖中华绒螯蟹(Eriocheir sinensis)养殖区"白膏症"发病症状、扣蟹的来源、投饵模式、水草覆盖率、螺蛳投入量、底泥状况、回捕率、产量等进行较为系统的调查。同时对病蟹进行寄生虫检查、病原微生物分离、回接攻毒及病变组织的电镜观察等病原学研究,结果未发现致病性生物。调查结果表明,中华绒螯蟹"白膏症"的发病率雄蟹显著高于雌蟹,其症状为甲壳发黄,头胸甲腹面下肝区发白色或青黑色,肝胰腺由正常的橘黄色变成淡黄或白色;症状严重的病蟹胸腔积水,肌肉松驰萎缩,肝胰腺呈糜烂状,鳃丝发黑。调查结果显示,"白膏症"的发生与饵料的投喂量、动植物饵料之比及水环境有着密切的联系。根据该病的主要症状及发病原因,认为该病应命名为中华绒螯蟹肝胰腺白化症。

Pathogenic factors of albinism in hepatopancreas of Chinese mitten crab Eriocheir sinensis (Decapoda:Grapsidae)

The Chinese mitten crab(Eriocheir sinensis) is an omnivorous species,and has great commercial significance in China.With the rapid development of intensive rearing,serious ecological and pathological problems are increasing in the crab producing regions.In recent years,a kind of disease in E.sinensis,called "BAIGAOZHENG Symptom" by local culturists occurred frequently in the intensive farming areas of east Taihu Lake and other regions.Main symptoms of diseased crabs were observed in hepatopancreas,gills and muscles,causing tremendous loss in crab farms,and the cause of diseases remained unclear.Therefore,since October 2002,by visiting individual culturist and collecting questionnaires,a systematic survey has been conducted to investigate the occurrence of the disease.The items surveyed included the sources of 2-year-old mitten crab larvae,feed casting patterns,coverage of aquatic plants,the amount of feed input,bed mud status,recapture rates,and commercial crab production.The results revealed that there was a marked gender difference in the incidence rate of albinism in hepatopancreas,and male crabs were significantly more prone to develop hepatopancreas albinism than the females.By examining the diseased male crabs for any abnormalities,the diagnostic symptoms or signs included that the smooth and intact body surface,yellowish carapace,dark purple hepatic region inside the breastplate,pale yellow or white hepatopancreas.Moreover,as the disease furthor developed,the hydrothorax in the thoracic cavity,loosen and shrunk muscles,rotten hepatopancreas,and blackened branchial filaments were commonly observed.In order to know the possible pathogens for albinism in hepatopancreas,isolation procedures were performed,and three bacterial strains from Aeromonas,Pseudomonas and Vibrion,were isolated from the hepatopancreas and gills.The challenge experiments with these bacterial strains reliably excluded possibility of the involvement of bacteria in the hepatopancreas albinism.Electronic microscope observation on diseased tissues also did not find any virus associated with it.These results,together with the absence of parasites in the diseased crabs,implied that "BAIGAOZHENG Symptom" disease was not caused by pathogenic microorganisms.Investigation results indicated that improper feed-casting brought malnutrition to the Chinese mitten crab,and made ambiance water degenerate.Therefore,the occurrence of "BAIGAOZHENG Symptom" disease,regarded as a nutritional disease,has close relation with feeding amount of feeds,ratio of animal to plant based feeds,and quality of ambiance water.Based on the main symptoms and pathogenic factors,it is suggested that this disease be nominated scientifically as hepatopancreas albinism.