Japanese flounder(Paralichthys olivaceus)is a widely cultured economic marine fish species in China because of its fast growth,high value and good taste.As a consequence,more and more fish farmers participate in Japanese flounder aquaculture in recent years.However,high density of breeding makes it easy to cause water quality deterioration and a variety of diseases,and diseases of the cultured fish have occurred frequently and infectious disease brought huge economic losses.What is more serious is that this limits the profitability and development of Japanese flounder aquaculture.Therefore,to breed new flounder strain with enhanced disease resistance and growth rate is an important task in marine fish aquaculture.In this paper,we focused on the detection of different disease resistance ability,during the course of Edwardsiella tarda infection,56 families were established.Among them,32 families were used in the experiment of infecting E.tarda.The purpose of this experiment was to screen families with high disease resistance to E.tarda so that we could solve the problems caused by the traditional methods of treating disease,such as drug residues,environmental pollution and drug resistance.Disease resistance was evaluated in 32 families through intraperitoneal injection of bacterial E.tarda.Before formal challenge experiment,we did a preliminary infection experiment to measure the half lethal concentration of E.tarda to Japanese flounder.According to the results of preliminary experiments,we determined the half lethal concentration(LD₅₀)to be(3.69×10)⁵ CFU/mL.Then 75 fishes were randomly taken from each family and injected with the bacteria according to the half lethal concentration of solution,0.2 mL/10 g body weight.Water temperature should be controlled at(19±1)℃.4 800 fishes from 32 families were challenged with E.tarda through intraperitoneal injection.Through the analysis we know that their survival rate was between 8.2%-66.1% with an average rate of 31.2%.Results demonstrated that there was significant difference in disease resistance among different families(P<0.05).Six families showed high disease resistance to E.tarda.Moreover,we found that the families from family F0768 which had been considered to be highly resistant to Vibrio anguillarum in 2007 showed high disease resistance to E.tarda.So we speculate that the family F0768 has a good disease resistance to both of the bacteria.This study laid the foundation for the selection of E.tarda and V.anguillarum resistant Japanese flounder strains,which is of importance and has application value for the study of molecular mechanism of bacteria resistance and the selective breeding of disease-resistant new species.