Turnbull J, Corsin F, Mohan CV, Padiyar PA, Thakur PC, Madhusudan M, Hao NV & Morgan KL (2005) Optimising Emergency Harvest Strategy for White Spot Disease in a Semi-Intensive Penaeus monodon Culture System in Karnataka, India. In: Walker P, Lester R & Bondad-Reantaso M (eds.) Diseases in Asian Aquaculture V. Diseases in Asian Aquaculture, 5. Fifth Symposium on Symposium on Diseases in Asian Aquaculture, Brisbane, Australia, 24.11.2002-28.11.2002. Manila, Phillipines: Asian Fisheries Society, pp. 405-414. http://www.fhs-afs.net/daa_v_proceedings.htm
Abstract A longitudinal study of 70 semi-intensive shrimp farms was undertaken in Karnataka, southwest India. For the purpose of this study white spot disease (WSD) was defined as the observation of 5 or more moribund or dead shrimp at the side of the pond on a single day and detection of white spot syndrome virus (WSSV) by 1-step PCR or histopathology in harvested shrimp. Samples were collected from 62 ponds at harvest and 31 fulfilled the case definition. In this system WSD had a significant effect on the average length of production cycle, yield and weight of the shrimp at harvest. Farmers have tried to reduce losses from WSD through avoiding risks and harvesting in the face of an outbreak. However, the information available on which to base such strategies can be misleading. Neither stocking WSSV positive (2-step PCR) post-larvae nor the presence of WSSV (2-step PCR) in shrimp from cast net samples 6 weeks after stocking were significantly associated with the length of the production cycle, yield, average weight at harvest, the risk of either WSSV presence at harvest or WSD. The findings indicate that WSSV and shrimp with WSSV inclusions by histopathology can be present in the pond without progressing to a full pond level outbreak of WSD. A decision-making tool based on the incidence and clinical signs of dead or moribund shrimp at the side of the pond allowed WSD to be predicted with an estimated sensitivity of 93.8% and a specificity of 94.3%. The implication of these findings for informing decisions on harvest strategy is discussed.