Performance of WSSV-infected and WSSV-negative Penaeus monodon postlarvae in culture ponds

In a survey of 27 Penaeus monodon culture ponds stocked with postlarvae (si milar to PL10) at medium density (similar to 40 shrimp m(-2)), single-step nested white spot syndrome virus (WSSV) PCR was used to measure the WSSV in fection rates in the shrimp populations within 1 mo after stocking. Seven p onds were initially WSSV-free, and the shrimp in 5 of these were harvested successfully. In the ponds (n = 6) where detection rates were higher than 5 0 %, mass mortality occurred during the growth period, and none of these po nds was harvested successfully. In a subsequent study, P. monodon brooders were classified into 3 groups according to their WSSV infection status befo re and after spawning brooders that were WSSV-positive before spawning were assigned to group A; spawners that became WSSV-positive only after spawnin g were assigned to group B; and group C consisted of brooders that were sti ll WSSV-negative after spawning. WSSV screening showed that 75, 44 and 14 % , respectively, of group A, B and C brooders produced nauplii that were WSS V-positive. Most (57 %; 16/28) of the brooders in group A produced nauplii in which the WSSV prevalence was high (> 50 %). When a pond was stocked wit h high-prevalence nauplii from 1 of these group A brooders, an outbreak of white spot syndrome occurred within 3 wk and only similar to 20 % of the in itial population survived through to harvest (after 174 d). By contrast, 2 other ponds stocked with low-prevalence and WSSV-negative nauplii (derived respectively from 2 brooders in group B), both had much higher survival rat es (70 to 80 %) and yielded much larger (similar to3 x by weight) total har vests, We conclude that testing the nauplii is an effective and practical s creening strategy for commercially cultured P. monodon.