Changes in mortality and immunological variables of Litopenaeus vannamei parents and their filial families infected with white spot syndrome under different experimental conditions

In order to find changes in mortality and immunological variables of Litopenaeus vannamei parents and the filial WSSV-resistant and -susceptible families after infection with WSSV under different experimental conditions, the haemolymph total haemocyte count (THC), phenoloxidase (PO), and superoxide dismutase (SOD) activities were measured at days 0, 1, 3, 6, 9, 12 and 15 after challenge and shrimp mortality was also recorded. When shrimps were challenged with 10−3 (1.29 × 106 copies mL−1), 10−4 (1.29 × 105 copies mL−1) or 10−5 (1.29 × 104 copies mL−1) WSSV stock solution (0.1 mL shrimp−1), the cumulative mortalities (mean ± S.E.) on day 15 were 100 ± 0%, 79.3 ± 1.1%, and 21.7 ± 2.3%, respectively. Among shrimps challenged with 10−4 (1.29 × 105 copies mL−1) WSSV dilution (0.1 mL shrimp−1), the cumulative mortalities (mean ± S.E.) on day 15 in high-density (100 shrimps m−3), middle-density (50 shrimps m−3), and low-density (25 shrimp m−3) groups were 95.5 ± 0%, 84.7 ± 0%, and 72.3 ± 0%, respectively. The immunological variables including THC, PO, and SOD were decreased significantly at the beginning of infection stage, while these immunological variables for survivors reached almost the similar levels to the non-infection control group on day 15 after challenge with 10−4 (1.29 × 105 copies mL−1) WSSV dilution (0.1 mL shrimp−1). Cumulative mortality (mean ± S.E.) on day 15 in 17 filial families (G2) ranged from 13.3 ± 1.9% to 100 ± 0% when shrimps were challenged with 10−4 (1.29 × 105 copies mL−1) WSSV dilution (0.1 mL shrimp−1). Although, the PO and SOD activities for shrimps in the WSSV-resistant family were slightly higher than those in the WSSV-susceptible family at the same sampling time after infection, these differences were not significant (p < 0.05).