Black tiger shrimp, Penaeus monodon, is among the economically important species in ASEAN and the world. As the tiger shrimp
industry in Malaysia is gearing towards the expansion and intensification, the increase of
luminous vibriosis cause by luminous bacteria seem become parallel to these aquaculture industry. Significant larval mortalities in Asean shrimp hatcheries are often associated with luminescent vibriosis which caused by Vibrio harveyi. The main source of luminous vibriosis is midgut contents of broadstock shed into the water with the eggs during spawning. The gut contents of broadstock and adult shrimp contained the highest number of luminous bacteria. Beside that, the near shore seawater may also be a major sources of infection. A total of 30 luminous bacteria were collected from commercial tiger shrimp farms in Terengganu, Kedah and Johor. 30 physiological and biochemical tests were carried out by using conventional methods to identify the 30 luminous bacteria. The biochemical and physiological results showed that all isolates belonged to Vibrio harveyi, forming rounded
colonies with smooth periphery and undulated colonies with rough periphery. Both types of colonies showed hemolysis of red blood cells and appeared green and yellow on thiosulfate-citrate-bile-salt-sucrose agar plate selective media. Most of the isolates have similar phenotypic characteristics; however there were differentiation in morphological appearance on tripticase soy agar plate, colony color on thiosulfate-citrate-bile-salt-sucrose agar plate, tolerance level to sodium chloride and ability to ferment sucrose. The distinct phenotypic characteristic possessed of the all isolates in this study were enable to grow well on the media without supplemented with sodium chloride.