EXPERIMENTAL INFECTIONS OF CRUSTACEANS WITH LUMINOUS BACTERIA RELATEDTO PHOTOBACTERIUM AND VIBRIO - EFFECT OF SALINITY AND PH ON INFECTIOSITY

Luminous bacterial shrimp diseases have recently become a major proble m in shrimp hatcheries in Indonesia and other Asian countries. Luminou s bacteria were isolated from moribund shrimp larvae from hatcheries i n Jepara in December 1990. These isolates consisted of two groups whic h were closely related to Vibrio harveyi and Photobacterium phosphoreu m. Pathogenicity tests demonstrated that several strains were pathogen ic to Artemia nauplii and Penaeus monodon larvae at concentrations of 10(4) and 10(3) cfu/ml respectively, The virulence of the bacteria was related to the age of the larvae, such that 25.28% of zoea, 47.08% of mysis and 51.50% of postlarvae survived 48 h exposure to the pathogen . The bacteria were unable to cause significant mortalities to barnacl e and Macrobrachium larvae but were pathogenic to P. indicus larvae in dicating that they exhibit a degree of host specificity and that barna cles may be a potential reservoir for these disease-causing bacteria. Most outbreaks of luminous bacterial disease in Indonesia occur during the rainy season. Exposure of luminous bacterial pathogens to low sal inities ( 10, 15 ppt) for 12 h before use in immersion challenge exper iments with Penaeus monodon larvae resulted in significantly enhanced mortalities (P < 0.05). This may account in part for the seasonality o f luminous bacterial disease outbreaks. Exposure of luminous bacteria to acid pH (5.5) significantly reduced their pathogenicity toward pena eid prawn larvae (P < 0.05). These results imply that environmental fa ctors may play a key role in disease outbreaks.