Ulvan extract acts as immunostimulant against white spot syndrome virus (WSSV) in juvenile black tiger shrimp Penaeus monodon

Sixty Peneaus monodon shrimps (2.39±0.38 g) were divided into fifteen 250-L fibreglass tanks, fed with diets containing 0.0 (control diet), 500, 1,000 or 1,500 mg purified ulvan kg-1 diet for 14 days and were subjected to a white spot syndrome virus (WSSV) challenge test, total hemocyte count (THC), respiratory burst activity (RBA) and phenoloxidase assay (PO). In the challenge test, viral strain displayed strong virulence which induced 100% mortality after 3 days. Prolonged survival was observed in shrimps fed with diet containing 1,000 mg purified ulvan kg-1 diet. Shrimp fed diets containing purified ulvan exhibited 77% higher THC than in those fed the control diet. Highest THC was obtained in shrimps fed the diet containing 1,500 mg ulvan kg-1 diet and lowest in those fed the control diet. This suggested that ulvan promoted the activation of cellular immunity in shrimps. Respiratory burst activity of shrimps in all diets containing the purified ulvan was significantly higher than of those fed the control diet. Phenoloxidase activity only became significantly high when shrimps were fed a diet containing purified ulvan at levels of 1000 mg purified ulvan kg-1 diet or more (i.e. 1500 mg kg-1 diet). No significant difference was observed in shrimp fed diet containing 500 mg purified ulvan kg-1 diet and those fed with the control diet. It suggested that adding ulvan at 1000 to 1500 mg kg-1 diet could stimulate hemocytic degranulation and activate prophenoloxidase to become phenoloxidase.