PRELIMINARY STUDY ON THE ETIOLOGY OF CHANNEL CATFISH INTUSSU SCEPTION DISEASE

Nowadays,a named "intussusception" disease in channel catfishes occurred in many latitudes of China.Besides haemorrhage symptom,the disease exhibit intestine shrinking,intussusception,rectocele phenomenon and so on.The disease mostly happened in spring and summer,sometimes in October,and it have resulted in so many channel catfish dead in China for years that menace the healthy culturing strictly.However,this disease has been analysed and studied by some domestic and international scholars,the undoubted nosogenesis has not been found now.Some scholars considered that intussusception disease was developed by Stenotrophomonas maltophilia,others deemed that it maybe not an independent one,only a familiar symptom in channel catfish.So far,formal coverage about other pathogenic bacteria in channel catfish has not been turned up.So,the etiology of channel catfish intussusception disease was studied preliminarily in this study through two kinds of diseased channel catfish suffered intussusception in China.In this study,two kinds of pathogenic strains named YDCC-5-1,0704CCBr and 0704CCl were isolated from the blood respectively,liver and brain of moribund channel catfish which suffered intussusception with integrated intestine collected from two different regions in Hubei Province.The two diseased fishes showed the similar symptom of haemorrhage:eyes,operculum,pars cephalica,the base of pectoral fin and pelvic fin hyperaemia,anus hyperaemia,and some suffered typical intussusception.The concentration of dissolved oxygen,union-ammonia and nitrite in the water areas of two diseases were all in margin of safety.The isolate YDCC-5-1 was identified as Aeromonas hydrophila controlled by Aeromonas hydrophila(XS91-4-1),and the isolates 0704CCBr and 0704CCl were identified as Pseudomonas fluoresces controlled by Pseudomonas fluoresces(56-12-10),respectively,through morphological observation,physiological and biochemical tests and analysis of 16S rDNA sequence.The strains XS91-4-1 and 56-12-10 were isolated and preserved by this laboratory,used as control strains in physiological and biochemical tests.The isolate YDCC-5-1 was identical with A.hydrophila in morphological observation,physiological and biochemical tests and analysis of 16S rDNA sequence:round colony,single thalli or bigeminal,bacilliform and Gram reaction negative,positive for motility,oxidatase,catalase,M.R and V-P reaction,fermented glucose,arabinose,sucrose and so on;16S rDNA sequence of YDCC-5-1 was 99% similar to A.hydrophila ATCC7966 in GenBank.The isolates 0704CCBr and 0704CCl grow at 4℃,not at 41℃,give birth to fluorescence pigment,oxidatase and catalase,fermented glucose,utilize glucose,fucose,sucrose,L-proline only as carbon source,Gram reaction negative,which were all identical with Pseudomonas fluoresces combined with analysis of 16S rDNA sequence.In addition,they were all proved to be pathogenic to experimental fish in the challenge testes.The two cases of channel catfish intussusception diseases were controlled by using antibiotics based on the drug sensitivity of these isolates.Thereinto,florfenicol was recommended to breed aquatics in Yidu Qingjiang,Hubei Province,and norfloxacin was commended to breed aquatics in Niushan Lake,Wuhan,Hubei Province,according as the result of the drug sensitivity of these isolates.According to our study results,new viewpoint and speculation of channel catfish intussusception disease was discussed,however,the further study should be continued rapidly.