Hari Babu, P (MAJOR)Neeraja, TMadhavan, NASHOK KUMAR, B2021-07-122021-07-122019-11https://krishikosh.egranth.ac.in/handle/1/5810170397THESESPacific white shrimp (Litopenaeus vannamei) is one of the most important cultivated shrimp species worldwide. However threat of various diseases is one of the biggest risk factors for healthy and sustainable development in shrimp aquaculture. Vibriosis mainly caused by Vibrio harveyi, Vibrio parahaemolyticus and Vibrio alginolyticus is the most prevalent bacterial disease in global shrimp farming. Healthy and infected/moribund shrimp samples were collected from three ponds in Nellore region of Andhra Pradesh from January, 2019 to March 2019. Vibrio spp. were isolated from the pond water and the hepatopancreas of healthy and infected/moribund shrimp using (TCBS) thiosulfate–citrate–bile salt–sucrose agar plate, and then identified by conventional biochemical tests. The dominant Vibrio type in healthy shrimp hepatopancreas were V. alginolyticus (41.6%), followed by V. damsela (25%), V. vulnificus (16.6%), V. mimicus (8.3%), V. anguillarium (4.1%) and V. ordali (5.5%). The concentration of Vibrios load in healthy shrimp hepatopancreas was ranged from 6.5×103-9.7×103 CFU/gm. Whereas seven types of Vibrio such as V. parahaemolyticus (45.8%), followed by V. harveyi (16.6%) and V. vulnificus (12.5%), V. anguillarium (8.3%), V. ordali (8.3%), V. mimicus (8.3%) and V. damsela (4.1%) were predominant in the hepatopancreas of infected/moribund shrimp samples. Vibrio load in infected shrimp hepatopancrease was ranged from 7.8×103 -10.5×103 CFU/gm. Total of six distinct Vibrio species such as V. parahaemolyticus (41.6%), V. alginolyticus (20.8%), V. harveyi (12.5%), V. mimicus (12.5%), V. ordali (8.3%) and V. anguillarium (4.16%) were identified from water samples. The number of Vibrio was ranged from 4.8×103_ 7.5×103 CFU/ml in water samples. Severe stress and injury to shrimp under poor environmental conditions lower their resistance, rendering them susceptible to opportunistic pathogens. Influence of turbidity, heavy organic matter plays a major role in the distribution of bacterial population in pond water. The present study showed that similar pond management and environmental parameters influenced Vibrio species composition in water both qualitatively and quantitatively. However healthy and infected (moribund) shrimp showing variation in occurrence of Vibrio at the time of sampling. This indicates, the healthy shrimp shows the selectively avoiding the pathogenic vibrios. At the same time the pond water is showing decrease in species diversity at 60 DOC. Similar observation was made by HH Sung et al (2001). In India there are nearly 80,000 shrimp farmers depended on shrimp farming and majority of these are small and marginal farmers. This study is aimed at educating these small and marginal farmers on Vibrio species dynamics at pond level so that the farmers can avoid misuse of antibiotics instead they depend on better management practices.EnglishThesis