Efficacy of ＂Sargassum oligocystum＂ Extract on the Innate Immunity of White Shrimp ＂Litopenaeus vannamei＂ and Its Resistance Against ＂Vibrio alginolyticus＂

This study was to examine immune response of white shrimp ＂Litopenaeus vannamei＂ and its resistance against ＂Vibrio alginolyticus＂ when shrimp received ＂Sargassum oligocystum＂ extract (SOE). Shrimp which had been immersed in seawater containing SOE at 300 and 500 mg/l for 4 h, hemocyte count and other immune parameters including phenoloxidase (PO) activity, respiratory burst (RB), superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, and lysozyme activity significantly compared to the control shrimp. The expressions of LGBP and PX, and mitotic index of hematopoietic tissue (HPT) of shrimp immersed in SOE at 100, 300 and 500 mg/l after 4 h were significantly higher than those of control shrimp. Shrimp immersed in 100, 300, and 500 mg/L SOE showed increased phagocytic activity and clearance efficiency to ＂V. alginolyticus＂. Shrimp which had been immersed in seawater containing 100, 300 and 500 mg/l SOE after 4 h were challenged with ＂V. alginolyticus＂ at 4.5 x 10^(6) colony-forming unit (cfu)/ shrimp, and then placed in seawater. The survival rate of shrimp immersed in 300 and 500 mg/l SOE was significantly higher than that of control shrimp over 12~120 h. In conclusion, shrimp immersed in seawater containing SOE at 300 mg/l increase resistance, phagocytic activity and clearance efficiency against ＂V. alginolyticus＂ as an evidence of increases in hemocyte count, other immune parameters, expressions of LGBP and PX, and mitotic index of HPT.