A TaqMan real-time PCR assay for quantifying white spot syndrome virus (WSSV) infections in wild broodstock and hatchery-reared postlarvae of fleshy shrimp, Fenneropenaeus chinensis

In the present study, a highly sensitive and specific TaqMan real-time PCR was developed to quantify white spot syndrome virus (WSSV) infections in wild broodstock and hatchery-reared postlarvae of fleshy shrimp, Fenneropenaeus chinensis. A total of 159 individuals of wild F. chinensis brooders from 3 locations were captured and 210 postlarvae (PL1–8) were obtained from seven commercial hatcheries in 2007 in South Korea. The WSSV infections in 3 broodstocks showed a wide range, from 0 to 2.28 × 106 (with a mean of 1.50 × 104) copies ng− 1 of DNA. Out of 159 brooders assayed, 39 (24.5%) were negative and 120 (75.5%) were positive; 153 (96.2%) showed less than 100 copies (mean 10.2 copies), 111 (69.8%) showed less than 10 copies and only 6 individuals (3.8%) showed high infections with a range of 2.36 × 102 to 2.28 × 106 copies ng− 1 of DNA. In 210 postlarvae, a range of 2.6 to 713.6 (with a mean of 220) copies g− 1 of DNA was observed. The mean WSSV copy number in the postlarvae was 7.9 × 105, which was equivalent to 8.5 × 105 copies mg− 1 of postlarvae weight. A total of 87.1% of postlarvae were WSSV positive and except for two hatcheries (H4 and H7), the postlarvae of all the other five hatcheries were positive.Even postlarvae from the same hatchery, especially of hatcheries H4 and H5, showed a wide range of WSSV infection resulting in higher infections than other hatcheries. There were 34.3% of the postlarvae assayed in the present study that showed very low infection, with less than 10 copies ng− 1 of DNA. Based on our results, it is recommended to pre-screen broodstock or larvae for selective breeding, stocking in production systems or stock enhancement.