Occurrence of four pathogenic Vibrios in Chinese freshwater fish farms in 2016

The purpose of this survey was to investigate the distribution of major pathogenic Vibrio spp. (Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio vulnificus and Vibiro cholerae) in Chinese freshwater fish farms. In total, 4064 samples of freshwater fish, water and sediment were collected from 12 provinces covering every quarter in 2016. The occurrence of Vibrios was as follows: V. cholerae (10.33%), V. parahaemolyticus (3.89%), V. alginolyticus (1.24%) and V. vulnificus (0.76%). Among 158 confirmed V. parahaemolyticus isolates, 44 isolates (27.85%) had virulence genes (trh/tdh). Among 420 confirmed V. cholerae isolates, 4 were the O1 stains and 4 were the O139 strains. Out of 112 freshwater farms, 58.93% had Vibrios-positive samples. The rates of Vibrios-positive samples from May to October (12.45%-35.20%) were higher than those in other months (0.00%-8.07%). Compared the environment factors of Vibrios positive and negative water samples, there was a significantly difference in temperature (P＜0.01), while no significant difference in salinity and pH value (P＞0.05). In summary, the study presents comprehensive contamination data on the occurrence of four major pathogenic Vibrios in freshwater aquaculture of China for the first time, and the results indicate that Vibrios are widely distributed in aquaculture environment and a further risk assessment is needed to conduct.