Effects of Water Temperature, Stocking Density, and Exposure Period on the Susceptibility of Whiteleg Shrimp (Penaeus vannamei) to Waterborne White Spot Syndrome Virus

In pond-based shrimp culture, seawater exchange may introduce white spot syndrome virus (WSSV) from coastal waters, but infection risk at a given seawater viral concentration may vary with temperature, stocking density, and exposure duration. This study evaluated waterborne WSSV susceptibility in whiteleg shrimp (Penaeus vannamei) under these conditions. Shrimp were reared at 25 or 30 °C and at low (70), medium (140), or high (210 shrimp/m2) stocking densities; physiological responses were assessed, followed by short-term and continuous immersion challenges and a cohabitation challenge. Higher stocking-density conditions were associated with stress-related physiological changes and greater WSSV susceptibility. Under short-term exposure, 107 WSSV genome copies/L caused infection only in the high-density group at 25 °C. Under continuous exposure, the minimum infective dose (MID) values were 105 and 104 WSSV genome copies/L at low and high stocking densities at 25 °C, and 106 and 105 WSSV genome copies/L, respectively, at 30 °C. Cohabitation transmission occurred at seawater viral loads below those associated with short-term immersion infection. By linking seawater viral concentrations with experimentally defined MID values and cohabitation-transmission outcomes, these results indicate that waterborne WSSV transmission risk should be assessed in relation to viral concentration, exposure duration, water temperature, and stocking-density conditions.