Experimental Vibrio harveyi infections in Penaeus vannamei larvae

A culture of Vibrio harveyi, isolated from diseased Penaeus vannamei, was pathogenic in penaeid shrimp larvae when used in a bath at 10⁵ cells ml^-1 for 2 h. The resultant disease had characteristics of Bolitas negricans, as observed in Ecuadorian hatcheries, namely the development of bioluminescence, reduced feeding and retarded development, sluggish swimming, reduced escape mechanisms, degeneration of hepatopancreatic tissue with resultant formation of necrotic bundles, and increased mortality. Koch's Postulates were confirmed by reisolation and identification of the organism. Histopathology showed the presence of distinctive melanotic tissue aggregates within the hepatopancreas, with immunohistochemistry confirming the presence of large numbers of V. harveyi in the intestine and hepatopancreas. These results indicate a suitable infection protocol, which can be used to test the pathogenicity of putative pathogens of penaeid shrimp larvae.