AN ECOLOGICAL STUDY ON EDWARDSIELLA-TARDA IN FLOUNDER FARMS

An ecological investigation on Edwardsiella tarda was carried out in t wo Japanese flounder (Paralichthys olivaceus) farms in Fukuyama City f rom April to December 1992. E. tarda was isolated from 86% of water, 4 4% of sediment and 14% of fish samples in one pond, and 22% of water, 0% of sediment and 2% of fish samples in the other pond, although epiz ootics caused by E. tarda were not observed in either pond. Serologica l studies proved that all the isolates off. tarda from flounder and it s environment shared a common heat stable O-antigen. Almost all the is olates tested exhibited pathogenicity to flounder by intramuscular inj ection. In survivability tests of selected isolates in sea water and f reshwater, they perished within 7 days in sea water but survived longe r period in freshwater. These results suggest that there is only one s erotype of E. tarda which has pathogenicity to flounder in the environ ment of flounder farms.