DAO 53:167-171 (2003)  -  doi:10.3354/dao053167

Seasonal variation in white spot syndrome virus-positive samples in broodstock and post-larvae of Penaeus monodon in Thailand

Boonsirm Withyachumnarnkul1,*, Vichai Boonsaeng1, Ranida Chomsoong2, Timothy W. Flegel1, Sithisuk Muangsin3, Gary L. Nash1

1Centex Shrimp, Chalerm Prakiat Building, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
2Department of Anatomy, Faculty of Medicine, Chiengmai University, 239 Huay Kaew Road, Chiengmai 50200, Thailand
3Phuket Aquaculture R&D Co. Ltd., 35/5 Mo 1, Thepratan Road, Phuket 83000, Thailand

ABSTRACT: Records of PCR test results for white spot syndrome virus (WSSV) were reviewed in Thailand from 1998 to 2000 for wild Penaeus monodon broodstock purchased by hatcheries and for post-larvae (PL) brought by farmers to diagnostic laboratories for testing. Samples for PCR comprised DNA extracts from the last pleopod dissected from broodstock females after the first spawning and DNA extracts from whole, homogenized PL. There was a consistent pattern of fluctuation in percentage of WSSV-positive broodstock and PL. In broodstock, the fluctuation pattern was similar each year, with a low percentage (0 to 6%) from January to May and a higher percentage (6 to 18%) for the rest of the year, with a peak from September to November. The fluctuation pattern for PL was similar but offset with peaks and troughs occurring approximately 2 mo after those for the broodstock. The peak percentages of broodstock-positive samples were roughly constant from year to year, but those for PL decreased progressively in magnitude from 1998 to 2000. Examination of a small number of hatcheries in 2000 revealed that the percentage of WSSV-positive PL samples was significantly lower for hatcheries that routinely discarded WSSV-PCR-positive wild broodstock when compared to hatcheries that did not.


KEY WORDS: WSSV · White spot syndrome virus · Prevalence · Broodstock · Post-larvae


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