IMMUNOSTIMULATORY EFFECT OF ULVAN OF Ulva fasciata ON Litopenaeus vannameii CHALLENGED WITH A SHRIMP PATHOGEN Vibrio parahaemolyticus

The present investigation was carried out to study the immunostimulatory effect of ulvan of Ulva fasciata on Litopenaeus vannamei through oral administration against Vibrio parahaemolyticus. The polysaccharide Ulvan from green seaweed Ulva fasciata was extracted and it was supplemented with pellet diets at three different concentrations (0.1, 0.2 & 0.3%). The ulvan supplemented diets were fed to shrimp Litopenaeus vannamei for 90 days and the growth performance was assessed. The weight gain and SGR of various concentrations (0.1-0.3%) of ulvan supplemented diets fed groups of shrimp were significantly (P< 0.05) increased than control group. After 90 days of feeding experiment, the L. vannamei were challenged with Vibrio parahaemolyticus and the mortality percentage was recorded daily up to 21 days. During the challenge test, the control group showed 80% mortality, but in the experimental groups, the mortality percentage was decreased from 51 to 26% in V. parahaemolyticus considerably (P< 0.05) with respect to the concentrations of ulvan. During the challenge experiment, the immunological parameters such as THC, prophenoloxidase activity, respiratory burst activity, superoxide dismutase activity, phagocytic activity, bactericidal activity and bacterial clearance ability of experimental groups were significantly (P < 0.05) increased than control group during the challenge study. The expression of immune genes such as β, 1, 3-glucan binding protein (ΒGBP), Prophenoloxidase, Peroxinectin (PE), Cytosolic superoxide dismutase (Cyt-SOD), Penaeidin-5 (PA-5), Single WAP domain protein (SWDP) and β-actin were significantly (P< 0.05) increased than control group during the challenge experiment. The V. parahaemolyticus load was enumerated from the infected shrimp at every 10 days intervals during challenge experiment. In control group, the Vibrio load was increased in hepatopancreas and muscle tissues from 10^th to 21^st days of challenge test. But in the experimental groups, the Vibrio load in both the tissues decreased positively from 10^th to 21^st days of challenge duration. It is concluded that the U. fasciata ulvan had enhanced the innate immunity and increased the resistance to pathogenic infection in shrimp L. vannamei.