Evaluation of dietary yeast derived mannan oligosaccharide for pacific whiteleg shrimp Penaeus vannamei: Effects on growth performance, immune response, hepatopancreas morphology and resilience to infection against Vibrio parahaemolyticus

With trends towards low fishmeal and higher plant ingredient-based diets for shrimp, there is consequently greater demand on feed additives to bolster the protein and nutrient profile quality for achieving more efficiency. Also, there is a need to enhance innate immunity and resilience to infection under intensive shrimp production scenarios. This investigation tested incremental levels 0, 0.2; 0.4; 0.6 and 0.8 % of a commercial yeast cell wall extract mainly comprising β-glucan and mannan oligosaccharides (MOS) (YM, YeaMOS, Angel Yeast, Yichang, Hubei, China) for post-larval shrimp Penaeus vannamei in isonitrogenous and iso-lipidic diets with proteinaceous plant ingredients amounting to 50 % contribution of the diet formulation. After 60 d, growth and feed utilization performance were not significantly affected in shrimp in terms of weight gain or FCR, but due to much higher survival, total biomass in groups of shrimps fed with dietary YM was higher compared to the control treatment. A sequential specific pathogen challenge test with Vibrio parahaemolyticus at final dose of 104 CFU mL−1 resulted in a marked improvement in survival against the control group with much enhancement at the inclusion level of 0.4 % YM (p<0.05). Before challenged, the total haemocyte count (THC) and the relative gene expression of Prophenoloxidase (ProPO) were higher in the group of shrimps fed with YM. Likewise, after infection, the amount of THC and ProPO remained better in the group of shrimps fed with YM. However, the 0.8 % YM treatment did not significantly differ from the control for phagocytic activity and index. The histomorphology condition of the hepatopancreas of shrimp before the infection for all treatments appears normal without significant numbers of hepatopancreatic tubules (T) and epithelial cell vacuoles (V). After pathogen challenge, all shrimp exhibited severe necrotic cell damage and massive sloughing of hepatopancreatic tubule epithelial cells into the lumen. Overall, giving YM as feed additives can improve the shrimp biomass and health, with the use of 0.4 % inclusion levels in practical diets for shrimp P. vannamei become the optimum dose to develop more efficient aquafeed production.