Detection of major bacterial and viral pathogens in trash fish used to feed cultured flounder in Korea

The possibility of trash fish food-direct pathogen infection to cultured flounder is a very important concern of fish farmers in Korea. A total of 26 groups of trash fish and shrimp samples were collected from 11 hatcheries on Jeju Island. Four groups and two groups of homogenized frozen trash fish samples were directly isolated and confirmed by PCR assays with S. iniae and S. parauberis, respectively. One iridovirus PCR positive result was obtained from one group of mixed trash fish samples. Phylogenetic analysis based on the MCP gene from one iridovirus strain was genetically closely related to seabass, red sea bream, rock bream, turbot, and Korean flounder iridovirus. Betanodaviruses were not detected from the trash fish samples. Based on these results, trash fish can be one of the sources or carriers of bacterial and viral pathogens for feeding cultured flounder in Korea.