Immunostimulatory Effects of Polysaccharide Compound from Seaweed Kappaphycus alvarezii on Asian seabass (Lates calcarifer) and it’s Resistance against Vibrio parahaemolyticus

Immunostimulatory Effects of Polysaccharide Compound from Seaweed Kappaphycus alvarezii on Asian seabass (Lates calcarifer) and it’s Resistance against Vibrio parahaemolyticus

Kappaphycus alvarezii is a red seaweed rich in polysaccharides. In the present study an attempt was made to isolate polysaccharide from K. alvarezii and also tested for immunostimulatory effects on Asian seabass (Lates calcarifer) using Vibrio parahaemolyticus as a test pathogen. Two sets of experiments were designed as mixed with fed diets and intraperitoneal (IP) injection of the crude extracts. Every five days of interval, the non specific immune responses were analysed by the parameters like WBCs count, Lysozyme activity and NBT assay. After 15 days of treatment, the animals were challenged against V. parahaemolytcius and cumulative survival rates were recorded. The total white blood cells were decreased in intraperitoneal injection of polysaccharides extract after 5^th day. But in fed diet cells count were significantly increased from 1^st to 15^th day. Fish fed diet with polysaccharide extract improved the lysozyme level than IP injection, which reduced simultaneously over the period compared with control. In the present study, the respiratory burst activity significantly enhanced in the fed diet polysaccharide extract in Asian seabass (Lates calcarifer) by oral administration and the highest activity reached in 0.5% fed diet on 15^th day. After challenge with V. parahaemolyticus, all treated groups showed a reduced mortality compared to the control group. The best survival rate was observed in the group polysaccharide extract treated with 0.5% by oral administration. Among the other groups, fish treated by intraperitoneal injection had a lower survival rate than the fish treated by oral administration. However, the differences between the two sets of experiment (oral administration or intraperitoneal injection) were only 10%. UV, FT-IR, ¹H and ¹³C NMR spectra were carried out to characterize the polysaccharide extract. The UV spectrum of the crude extract compound was showed a major peak at 282 nm. In FT-IR spectrum, major peak was observed at 1000-1100 cm^-1 supports the presence of ring vibrations C-O, C-O-C (polysaccharides region) and minor peak of 1647.93 cm^-1, which supports amide group. And based on the ¹H and ¹³C NMR spectra, the presence of carbonyl carbons in the purified compound was confirmed. Findings of the present study evidenced the excellent immunostimulatory activity of polysaccharide from the seaweed Kappaphycus alvarezii. Further complete purification and characterization of the active polysaccharide and its field evaluation is needed to bring this seaweed polysaccharide as a promising candidate for the development of good immunostimulatory agent in the field of aquaculture.