Vibriosis is a common bacterial disease in marine organisms. The first signs of vibriosis are usually anorexia and darkening of the whole fish. Vibriosis usually occurs in the warm summer months when the salinities and organic loads are high. Ortigosa, Esteve and Pujalte (1989) reported that the abundance of Vibrio harveyi andV. mediterranei were positively correlated with temperature, whereasV. pelagius counts showed negative correlation. Vibrio vulni¢ cus was isolated from seawater in Korea during the month of August only when the water temperature and chemical oxygen demand (COD) were high, but the pH and salinity low (Kim, Lee, Lee & Lee 1990). Isolation rate of V. cholerae increases with increased temperature and organic pollution (Redacliff, Hornitzky, Carson, Petersen & Zelski 1993). Vibrio alginolyticus was found in the water and attached to the copepodTigriopus fulvus during the warmest month (Carli, Pane, Casareto, Bertone & Pruzzo 1993).

Sea horses are used in Asian countries in traditional Chinese medicines. They are also popular in the global aquarium trade. Approximately, 20000000 sea horses are collected from the wild annually (Vincent 1996). In some areas, a 50% decline in the population over the last 5 years has been reported (Hilomen-Garcia 1999). Due to increasing demand and the potential extinction of sea horses, the Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC) in Iloilo, Philippines undertook breeding and seed production of the sea horse, Hippocampus kuda Bleekers1852. In 1999, sea horses 3^ 4 months old and 3^ 5 g in weight that were cultured in 1-tonne fibreglass tanks