However, disease outbreaks have caused seriouseconomic losses in several countries. According to a recentWorld Bank report, global losses due to shrim p diseases arearound US$ 3 billion (Lundin 1996). Vibrio species occur asthe dominant flora in various developmental stages of Penaeusmonodon and have been described as the causal pathogens(Lightner 1996; Sung et al. 2001).