The Establishment And Analysis Of High Disease Resistance To Edwardsiella Tarda And Thermotolerant Japanese Flounder (Paralichthys Olivaceus) Families

Japanese flounder (Paralichthys olivaceus)is a widely cultured economic marinefish species in China its fast growth, high valued and good taste. As a consequence,more and more fish farmers participate in Japanese flounder aquaculture in recentyears.However, high density of breeding make it easy to water quality deterioration anda variety of diseases,diseases of the cultured fish have occurred frequently and loses duoto infectious disease and brought huge economic losses in Japanese flounderaquaculture industry,What is more serious is that limit profitability and development ofJapanese flounder aquaculture.Therefore, to breed new flounder strain with enhanceddisease and growth rate is an important task in marine fish aquaculture.Temperature has a direct influence to fish growth, development, ingestion,metabolism, survival and distribution process life..Long-term evolution makes the fishhas its optimum temperature range, in this temperature range, the growth of fish reachthe best state. Many studies have shown that the growth of fish has significantcorrelation with temperature. Research has shown that if water temperature is above23℃，the Japanese flounder reduced ingestion, when the water temperature up to33℃,they live only briefly. In the southern province of northern coastal temperature is high,even in the north, summer water temperature will reach over25℃, need to use deepwell water to reduce, of course,it increases the production cost. Therefore, it isimportant to research the high temperature tolerance of Japanese flounder and its molecular mechanism for cultivating high temperature resistant strains and varieties, notonly can reduce the production cost, but also explore the relay breeding new model.Inthis paper, we focused on the detection of different disease， during the course ofEdwardsiella tarda infection,56families were established. Among them32familieswere used to the experiment of infecting Edwardsiella tarda.The purpose of thisexperiment was to screen high disease resistance families to Edwardsiella tarda so thatwe could solve the problems caused by the traditional methods treat the disease,such asdrug residues， environmentalpollution and drug resistance.Disease resistance wasevaluated in32families through intraperitoneal injection challenge with Edwardsiellatarda. Before formal experiment, we did a preliminary experiment to measure the halflethal concentration of Edwardsiella tarda to Japanese flounder. According to the resultsof preliminary experiments, we concluded that the artificial infection Edwardsiella tardahalf lethal concentration(LD50) which the study based on was3.69x105cfu/ml.Thenrandom sample75fishes from each family and take artificial injection the bacteria tothem according to the half lethal concentration of solution,0.2ml/10g body weightand set a repeated1time. The infection water temperature controled in19±1℃. As aresult that4800fishes was evaluated from32families through intraperitoneal injectionchallenge with Edwardsiella tarda. Through the analysis their survival rate was between8.2%～66.1%,while their average was31.2%. Results demonstrated that there wassignificantly difference in disease resistance among different families （P<0.05）.The results analyses of the sample for the test have shown that6families showed highdisease resistance to Edwardsiella tarda. what’s more we found that the families whichas the progeny of family F0768have more disease resistance than susceptive, showedhigh disease resistance to Edwardsiella tarda. Furthermore, we have proved that thefamily F0768also showed high disease resistance to Vibrio anguillarum. So wespeculate that the family F0768has a good disease resistance performance to two kindsof bacteria. The study of two kinds of bacteria by family selection in terms of fishdisease resistance breeding has not been reported so far, of course, including multiple bacteria. It is very important to breed new varieties of Japanese flounder that isresistant to Edwardsiella tarda and Vibrio anguillarum because of its great significancein research about new varieties of Japanese flounder with the ability of resistant multi-disease. This laid a foundation for our work of breeding new multi-disease resistancevarieties; At the high temperature stress of32℃under,21family’s survival rates wasbetween0~47.1%, the average survival rate was19.3%, among them, the five familyF1244, F1247, F1210, F1242, F1244and F1259’s survival rate is more than35%,significantly higher than the other groups, it was be defined as thermotolerant family,while these three family F1255, F1225and F1230, all individuals died, mortality ratewas100%,we named family whose survival rate is less than10%of the defined heatsensitive family. Resistance to high temperature, the average survival rate was43.2%and heat sensitive family only0.041%, both extremely significant difference (P <0.01).This experiment obtained five thermotolerant family, found that the offspring ofF0719family’s high temperature resistant performance is good.