INNATE IMMUNE-STIMULATING, IMMUNE GENES UP-REGULATING AND WHITE SPOT SYNDROME VIRUS RESISTANCE-ENHANCING ACTIVITIES OF ALGINATE FROM Sargassum siliquosum IN PACIFIC WHITE SHRIMP Litopenaeus vannamei
The Total Haemocyte Count (THC), Phenoloxidase (PO), Superoxide Dismutase (SOD) activity, Phagocytic Activity/Index were examined after feeding the white shrimp Litopenaeus vannamei with diets supplemented alginate at 0 (control), 2.0, and 4.0 g kg-1 for 14 days. Immune-related genes expression was evaluated by quantitative Real Time PCR (qRT-PCR). Results indicated that the immune parameters of three treatments directly increased when compared to the control. Before wssv infection, the three immune-related genes expression i.e. Toll, Lectin and proPO were up regulated. The wssv at 1 x 105 copies shrimp-1 was challenged at 14 day and the copy number of virus were examined quantitatively (qRT-PCR). The lectin gene were up-regulated post infection, and the Toll-gene in all treatments were down regulated. In a separate experiment, white shrimp L. vannamei, which had been fed diets supplementing the extract for 28 days, were challenged with white spot syndrome virus (WSSV) at 1 x 105 copies shrimp-1 and then placed in seawater. The survival rate of shrimp fed the alginate supplementd diets was significantly higher than that of shrimp fed the control diet at 24-120 h postchallenge, while the weight gain at the end of experiments were similar in all treatments. At 120 h postchallenge, the shrimp with diets supplemented sodium alginate at 4.0 g kg-1 treatment exhibit the best results on survival. It is therefore concluded that the supplementation of alginate of Sargassum siliquosum on the diet of L. vannamei enhanced the innate immunity and the expression of immune-related genes. The supplementation of sodium alginate were also able to improve the survival as well as the resistance against wssv infection. It is the first report on the simultaneous evaluation on the capability of alginate to enhance innate immune parameters, immune-related genes expression as well as the resistance against wssv infection in L. vannamei.