Prevalence of vibrios with special reference to Vibrio parahaemolyticus in farmed penaeid shrimp, Penaeus vannamei (Boone, 1931) from selected districts of Tamil Nadu, India

Prevalence of Vibrio spp. with special reference to Vibrio parahaemolyticus (Vp) infection was assessed in Penaeus vannamei farms in Kancheepuram and Thiruvallur districts of Tamil Nadu during the period August 2014 to February 2015. Isolation and identification of bacteria from haemolymph, stomach and hepatopancreas of P. vannamei was done from all the farms for the prevalence of Vp infection. Based on the morphological, physiological and biochemical characterisation, 74 isolates were identified as Vp (35.14%), V. harveyi (21.62%), V. anguillarum (16.22%), V. campbellii (10.81%), V. mimicus (8.11%), V. alginolyticus (5.41%) and Pseudomonas aeruginosa (2.7%). The PCR results showed that there were 26 (35.14%) isolates positive for Vp specific toxR and tlh genes and negative for human pathogenic tdh and trh genes. All isolates were also negative for acute hepatopancreatic necrosis disease (AHPND) specific AP1, AP2, AP3 (pirAvp) and AP4 (pirAvp and pirBvp) genes. The study revealed that there was no AHPND causing Vp strain in farmed P. vannamei from two important coastal districts of Tamil Nadu, India.