White shrimp Litopenaeus vannamei immersed in seawater containing Sargassum hemiphyllum var. chinense powder and its extract showed increased immunity and resistance against Vibrio alginolyticus and white spot syndrome virus

This study was to examine the immune response of white shrimp Litopenaeus vannamei and its resistance against Vibrio alginolyticus and WSSV when shrimp received the Sargassum hemiphyllum var. chinense powder and its hot-water extract. Both powder and extract showed activation of prophenoloxidase and generation of superoxide anion in the shrimp in vitro. The haemocyte count, phenoloxidase (PO) activity, respiratory burst, and lysozyme activity were examined after the shrimp were immersed in seawater containing S. hemiphyllum var. chinense powder or its extract at 0, 100, 300, and 500 mg L−1 for 1, 3, and 5 h. These immune parameters of shrimp immersed in 300 and 500 mg L−1 powder, and 100 and 300 mg L−1 extract were significantly higher than those of control shrimp after 3 h, but slightly decreased after 5 h. In another experiment, shrimp immersed in seawater containing the powder or the extract at 0, 100, 300, and 500 mg L−1 after 3 h were challenged with V. alginolyticus at 8 × 105 colony-forming unit (cfu) shrimp−1, or challenged with WSSV at 1 × 105 copies shrimp−1, and then placed in seawater. Survival rate of shrimp immersed in 500 mg L−1 powder was significantly higher than that of control shrimp after 24–120 h in the V. alginolyticus-challenge test, and after 72 h in the WSSV-challenge test, respectively. Survival rate of shrimp immersed in 300 mg L−1 extract was significantly higher than that of control shrimp after 72–120 h in both V. alginolyticus-challenge and WSSV-challenge tests. It was concluded that the shrimp immersed in seawater containing the powder at 500 mg L−1, and the extract at 300 mg L−1 had increased immunity and resistance against V. alginolyticus infection, and the shrimp that received extract at 300 mg L−1 showed resistance against WSSV infection.