Peptidoglycan as a Bioactive Functional Dietary Supplement Enhances Growth, Improves Nutrient Digestion, Increases Cellular Energy Allocation, and Activates Viral Resistance of Juvenile Penaeus monodon.

Immunostimulants are widely used in aquaculture to prevent diseases and have also been observed to promote growth in aquatic animals. The current study investigated the growth-promoting mechanism of dietary peptidoglycan (PG) in black tiger shrimp (Penaeus monodon). PG was supplemented into the experimental diets at varying concentrations (0.00, 0.10, 0.20, and 0.40 g·kg-1 of feed) and administered to the shrimp over a 60-day feeding trial. Shrimp growth in terms of weight gain and specific growth rate, total feed intake, feed conversion efficiency, protein efficiency ratio, and survival was monitored during the feeding trial. Immune parameters and shrimp viral resistance against white spot syndrome virus (WSSV) were also assessed. Results showed that supplementation of 0.20 g PG kg-1 diet enhanced shrimp growth compared with the control. This is supported by the biochemical analyses (nutrient retention, feed digestibility, digestive enzyme activities, and cellular energy allocation) showing improved feed conversion efficiency and lipid retention resulting from improved apparent dry matter digestibility of the diet, enzyme activities, and energy allocation in shrimp provided with 0.20 g PG kg-1 diet compared with the control. Furthermore, the 0.20-g PG kg-1 diet also resulted in the highest survival rate in the WSSV challenge test compared with the control and other PG-treated diets. This enhanced resistance was associated with an elevated total hemocyte count, increased respiratory burst activity, and increased phenoloxidase activity compared with the control. Collectively, the present data suggest that immunostimulant supplementation at 0.20 g PG kg-1 diet has growth-promoting effects in juvenile P. monodon.