Isolation of the bacterium, vibrio harveyi from cultured shrimp, penaeus monodon and production of vaccines against the bacterium

Abstract

Disease outbreaks detected by the presence of a large number of luminescent post larvae in larval rearing tanks followed by heavy mortalities, have been recorded in most of the shrimp hatcheries in Sri Lanka. Broad spectrum antibiotics, probiotics, and occasionally, imported vaccines have been used indiscriminately to control the disease. In this study, a pathogenic bacterium causing luminescence and heavy mortalities in post larvae was isolated from seven shrimp hatcheries situated in the North Western Province. The bacterium was characterized and identified as a strain of Vibrio harveyi using standard microbiological tests and biochemical reactions of bacteria. Two vaccines (Formalin killed and heat killed bacteria) were prepared from the isolated strain of V. harveyi and two groups of eighteen day old healthy post larvae (Pl18) were vaccinated separately by immersion technique. Efficacy of both vaccines were then evaluated by challenging vaccinated post larvae after different week intervals from vaccination with the same bacteria. Mean percentage survival of post larvae vaccinated with formalin killed vaccine and heat killed vaccine after 3 weeks from vaccination were 81.62% and 80.22% respectively which were significantly higher (p < 0.05) than that of the post larvae which were not vaccinated and used as the control (35.21% and 37.89%) confirming that the vaccines were effective.