The Pathological Characteristics Of Intussusception Disease Of Ictalurus Punctatus And Its Prevention

Ictalurus Punctatus,a superior variety of freshwater aquaculture,was introduced to China in 1984.Currently,it has been widely cultured in more than 30 provinces and has formed a trend for industrial aquaculture.Since 2006, a communicable disease attacked Ictalurus punctatus in cage culture in Zhexi reservoir and Wuqiangxi reservoir,Hunan province.The disease has the characteristics of sudden morbidity,high mortality,and fast infection.The typical pathological characteristics were round,oval or irregular fade spots distributed on the body surface,ascites,and enteritis after intestinal intussusception.This disease caused a serious loss for the Ictalurus punctatus culture.According to the incomplete statistics,the economic loss caused by the above disease in Zhexi reservoir in 2006 reached up to 100 million,the corresponding loss in 2007 was more than 500 million.Because of bankrupt for many farmers,and it was serious to contuse the enthusiasm of Ictalurus punctatus culture for farmers.This thesis investigated the pathological characteristics,epidemiological manifestation and its prevention and control measures.The purposes were to obtain a clear understanding of the pathogenic features and epidemiological manifestation,to provide a scientific basis for effective diagnosis and prevention of the disease.In the present study,3 pathogenic strains(C0601, C0602,C0603) were isolated from the intestine,liver,kidney of Ictalurus punctatus that was infected by the communicable disease.It was verified that C0601 was pathogenic strain causing intestinal intussusception for Ictalurus punctatus.The results from observation of bacteria morphology and determination of physiological and biochemical characteristics showed that C0601 is non-fermented,facultatively aerobic,gram-negative straight bacillus with peritrichous flagella.Except for maltose and mannose,this strain can not use other sugars to produce acid.The oxidase,MR,VP and H₂S ware negative, DNA enzyme,protease,urease and lysine decarboxylase were positive.The strain,C0601,was identified as Stenotrophomonas maltophilia. The results from sensitivity test showed that Stenotrophomonas maltophilia,was highly sensitive to florfenicol,sulfamethoxazole,sulfisoxazol, azithromycin,lomefloxacin,sulfamethoxazole compound,doxycycline.It was moderately sensitive to sarafloxacin hydrochloric and tetracycline norfloxacin and low sensitive to gentamicin and amikacin.Meanwhile,the strain showed drug resistance to penicillin,streptomycin and midecamycin.The epidemiological results demonstrated that Ictalurus punctatus infected by Stenotrophomonas maltophilia has the characteristics of sudden morbidity, high mortality,and fast infection.The peak infection occurred from March to May.Thereafter,less infection occurred.The pathological results further revealed that the infected Ictalurus punctatus had surface hyperaemia,bleeding and faded spots,abdominal enlargement,yellow or bloody ascites filled in intra-abdominal,congestive gastrointestinal mucosa,bleeding,yellow or bloody mucus filled in intestine,intussusception and even intestinal exfoliation. The results of medical remedy verified that cotrimoxazole,florfenicol pathogens is a very sensitive drug.If used in the early infection stage,both cotrimoxazole and florfenicol medication for about 8 days can control the disease.In peak infection stage(from March to May),hot polygonum(fresh or hay grass) addition in the channel cage culture can maintain the remedy effectiveness.Otherwise,the recurrence infection will occur.However,in the later stage of infection,the mortality rate of Ictalurus Punctatus in channel cage culture can reach up to 90%because of difficult feeding.