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

Abstract

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 (PL 1–8) 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 × 10 6 (with a mean of 1.50 × 10 4) 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 × 10 2 to 2.28 × 10 6 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 × 10 5, which was equivalent to 8.5 × 10 5 copies mg − 1 of postlarvae weight. A total of 87.1% of postlarvae were WSSV positive and except for two hatcheries (H 4 and H 7), the postlarvae of all the other five hatcheries were positive. Even postlarvae from the same hatchery, especially of hatcheries H 4 and H 5, 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.