Water samples from randomly selected shrimp hatcheries were enumerated for mean total Vibrio count (MTVC) while obtaining mean percentage of cumulative mortality (MPCM) for different larval stages. Pathogenecity of Vibrio isolates was studied on mysis larvae and post larvae by challenging with four concentrations (102 to 105 CFU mL-1). Significantly higher MTVC was recorded for broodstock maturation and spawning tanks. Artemia hatching tanks had the highest MTVC (1.67 × 104 CFU mL-1). Feeding mysis with Artemia nauplii, increased MTVC significantly in mysis tanks. Artemia nauplii and broodstocks are the major sources of contamination. MTVC in rearing water were positively related to MPCM of larvae. The most common species of Vibrio were V. parahaemolyticus, V. alginolyticus, V. harveyi, V. vulnificus and V. fluvialis; pathogenecity of former three species were greater on mysis II, the most pathogenic being V. parahaemolyticus (97.5% MPCM at 48 hours post challenge with 105 CFU mL-1). V. alginolyticus was the most pathogenic species to Pl12 (77.75% MPCM) followed by V. harveyi and V. parahaemolyticus. All five species showed varying degree of resistance to the tested antibiotics. In order to control pathogenic Vibrio and to reduce larval mortality, strict bio-security measures and best management practices are recommended.
2016 The Japanese Society of Fish Pathology