Based on four surveys at Nha Phu lagoon, Khanh Hoa province in 2003 showed that densities of pathogenic bacteria (Vibrio, Fecal coliform and Shigella- Salmonella) were not high. Almost data of density of pathogenic bacteria collected at stations had not exceeded the limits of water quality in coastal environmental yet (28TCN193-2004). However, some pathogenic species including Vibrio anguilarum, Vibrio vulnificus and Vibrio alginolyticus were found in some stations where there are relationship between quality of oyster aquaculture products and pathogenic bacteria. The result indicated that densities of epiphytic pathogenic bacteria in oysters were rather high with the densities of Fecal coliform, Shigella- Salmonella and Vibrio were 9-46
5-58
and 21-571 cfu/gr. respectively. The research also found that oyster products were not infected by paihogenic bacteria if they were collected in August and September when it was not rainy. Hence, the choices of breading and harvesting were necessary and suitable to reduce negative effects of pathogenic bac[eria on oyster farms.