| Trionyx sinensis is one of the special aquaculture varieties in China and can be found in everywhere of China except Ningxia,Xizang province for the extreme conditions.Before 1970s,the needs of the market was not too much,the fishing quantity of Trionyx sinensis could meet the market demands.The culture of Trionyx sinensis got its best time in 1990s,and the yield reached the highest.The occurrence of disease in Trionyx sinensis has become more frequent since the scale of aquaculture enlarged.Whether bacterial disease,viral disease or parasitic disease,it can cause a devastating attack on the aquaculture of Trionyx sinensis.So it’s quite important to study the disease of Trionyx sinensis for prevention and control of epidemic disease.In this study,a kind of bacterial sarcoidosis of Trionyx sinensis was used as a subject.The basic situation of sarcoidosis was explored by epidemiological investigation.Traditional identification methods and modern molecular biological methods were used to analyze and identity the pathogens of disease.Drugs sensitivity test were carried out on the isolated pathogen.A practical prevention and control scheme for the prevention and control of sarcoidosis was provided in combination with the actual aquaculture situation.The main results of this study are as follows.1.Investigation of the incidence of sarcoidosis in Trionyx sinensisThe incidence of sarcoidosis was investigated by visiting consultation,field investigation,laboratory inspection,data inquiry and so on.The results of the survey showed that sarcoidosis of Trionyx sinensis was common in the culture area of Trionyx sinensis in Liaocheng,Shandong.The disease was frequently occurred in the aquaculture area of the pond,and that cultured in greenhouse rarely occurred.Though the greenhouse and pond environment were quite different in temperature and light,nothing was done when they transferred the site of Trionyx sinensis.The incidence would last to the winter since the Trionyx sinensis translated from the greenhouse to pond.The temperature was high dring July and October,when the incidence was always found.Morbidity of the sarcoidosis was about 11%,and the mortality was low.The trauma of the sicken Trionyx sinensis was high,which could be up to 90%.The water ndexes were in the normal rangequality except the ammonia and nitrogen indexes.Anorexia,swelling of the body,whiteplate and mental malaise.were the main symptoms of the sarcoidosis.The anatomical results show that the sarcoidosis were often found in the lung,liver and limbs,and the sarcoidosis could be generally visible from the body.The nodules of the heart,mesentery and head were seen occasionally.There is a bean dregs like substance and the outflow of pus with malodour if the nodules were pierced.The surrounding tissue of the nodules of the lung,liver,and heart is accompanied by tissue hardening.The mesentery was more normal,and the tissue around the muscles of the extremities was looser.2.Screening and identification of the pathogeny of sarcoidosis in Trionyx sinensisThe dissociated nodule content was screened for the pathogen in aseptic condition.The parasites and fungi were detected by microscopic examination,the virus was detected by the regression infection experiment and electron microscopy,and the bacteria were detected by separating and purifying and attacking the virus.The results showed that No parasites,fungi or viruses were detected.Two dominant strains DM1 and DM2 were obtained by multiple separation and purification.Regression infection test was based on Koch’s law.The experimental group was treated by two ways of daily intraperitoneal injection and immersion.There was no abnormality in the immersion group,and no deaths or nodules were found in the DM2 injection group.The experimental bacterial concentration was 2.877×10~1-2.877×10~5 CFU/mL.The mortality rates of DM1injection group from low concentration to high concentration were 0%,25%,40%,70%,100%respectively.The experiment lasted 18 days.No nodules were found except for the highest concentration,and nodules were found in the other experimental groups.By setting a regression infection test,the pathogen was identified as bacterial DM1.The results of the phylogenetic tree of 16S rRNA showed that DM1 bacteria were clustered with Salmonella typhimurium and Salmonella paratyphi B as one and the similarity was100%.The pathogeny of Salmonella was determined to be Salmonella typhimurium by the physiological and biochemical experiments.3.Histopathological observationPathological section showed that nodules in the Trionyx sinensis included the capsule and the inner eosinophilic coagulating necrosis.The outer tissues of lung and liver nodules showed severe proliferation of cells and connective tissue.The muscles of the extremities were interposed with normal muscle tissue and necrotic muscle.The nodular capsule was formed by fibrous connective tissue.The envelope of nodules in the lung,liver,limbs and myocardium were thicker than that were found in the mesentery,which could be caused for connective tissue in the mesentery.Eosinophilic coagulation necrosis could be found in the nodules that occurred in the lung,liver and the mesentery.Some connective tissue would be found in the mesenteric nodule.Villous tissue formed by the single layer of columnar epithelial cells was seen in the cardiac nodules.4.Source analysis and drug sensitivity test of Salmonella typhimuriumThe selective culture medium of Salmonella typhimurium was screened for feed,water quality and silt,and the three cases were screened by source of Salmonella typhimurium.It was found that the most pathogenic bacteria were found in the bottom silt.The results of 34 kinds of antibiotics susceptibility of Salmonella Typhimurium showed that the bacteria were sensetive to amikacin,gentamicin,ciprofloxacin,cefoperazone and other 14 kinds of drug sensitivity;moderately sensitive to furazolidone,cephalexin;of norfloxacin,rifampicin and ampicillin and other 18 kinds of drug resistance.We could infer that the following aspects of the sarcoidosis occur in the following aspects through the collection of local delivery of seedlings,aquaculture production,cleaning data and pathogenic source analysis.Deteriorate of Trionyx sinensis’offspring seed.The anti stress response in greenhouse turned to nature pond were not well done.Excessive density led to severe trauma.These factors caused the disease of Trionyx sinensis to be easily infected by the pathogen.Too much mud on the bottom of the pond led to more Salmonella typhimurium.It eventually led to the occurrence of sarcoidosis in Trionyx sinensis. |
