| The pathogen that caused canker on large yellow croaker was mainly Vibrio alginolyticus,Vibrio harvey and Vibrio parahaemolyticus. Only when these pathogens bred and accumulated to acertain extent, they began to affect the normal life on fish and to damage the organization,ultimately lead the fish to illness. Therefore, to achieve the forecast warning of disease, it is criticalto detect the pathogenic organisms in early phase according to the epidemiology of disease, also toanalyze infection status and the trend of increase and decrease. In this research, we took the threekinds of pathogenic vibrio as the research object, carried out the molecular epidemiologicalinvestigation to prevent and control the diseases of cultured large yellow croaker and to play apositive role in early warning of disease.In this study, we selected the large yellow croaker breeding sea area for laboratory, which wasin Huangbi’ao, Xiangshan of Zhejiang province. We chosen three groups cages that fed with fishand shrimp or other fresh bait, respectively yearlings, two years, three years old fish; two years oldfish as one group that fed with formula feed. During2012-2013, we collected10fish in eachsentinel cage randomly. The liver, kidney, spleen, muscle were sheared from each fish to extracttotal DNA. Then, we detected and analyzed the infection status by multiplex PCR. Each timecollecting the fish, we also tracked and monitored the physicochemical and biological factors ofwater in the breeding cage and central waterway, including water temperature, salinity,transparency, dissolved oxygen, pH, phosphate, nitrate, total nitrogen, total phosphorus,COD, TOC, chlorophyll-a, the number of total vibrio, fecal coliforms and other indicators.The result showed that there were some differences between the three kinds of pathogenicvibrios that infected on the large yellow croaker. The infection rate of V. alginolyticus and V. harveyon fish was higher than V. parahaemolyticus.The three vibrios were more susceptible to muscle,spleen than to the liver and kidney. The infection rate on different age of fish was not identical.There existed infection rate in every sampling time. From July to September was the peak ofinfection and the infection rate increased after the typhoon certainly. The correlation between thedifferent diets and the infection of vibrio was not strong. The result of vibrio plate culturing and bymultiplex PCR technique in detecting the infection rate showed a similar trend, but the prevalenceof the former was lower than those of the latter.According to the correlation between the environmental factors and the infection rate of threepathogenic vibrios on large yellow croaker, it showed that the water temperature and the infection rate of V.harvey and V. parahaemolyticus had a highly significant correlation (P <0.01), while theinfection rate of V. alginolyticus was significantly associated (P <0.05). The total number of vibrioin water and the infection rate of V.harvey had extremely significant positive correlation, while theinfection rate of V. parahaemolyticus was significantly correlated. The correlation between otherenvironmental factor and the infection rate of three vibrios was not strong.In addition, according to the two years investigation on the relationship between occurrence ofcanker and the prevalence of pathogenic vibrio, it showed that the infection rate of vibrio on thelarge yellow croaker would reach a higher value a few days ago before the outbreak of canker in alarge area. So we could speculate the possibility of disease occurrence through investigating andanalyzing the infection rate of three pathogenic vibrios on large yellow croaker. Especially whenthe tissues were detected a higher prevalence of vibrio, we should remind farmers to take activemeasures to ensure the prevention and control of the disease. The result of this study would provideexperimental and theoretical basis to build prediction and early warning model of canker incultured large yellow croaker. |
