Biofloc technology with addition of different carbon sources altered the antibacterial and antioxidant response in Macrobrachium rosenbergii to acute stress

The objective of this study was to evaluate the immune response of Macrobrachium rosenbergii to acute stress, including the pathogen challenge, acute H2O2 and pH stress, to explore the application of biofloc systems in prawn farming. All 780 prawns (0.19 +/- 0.01 g) were randomly distributed into one control group with 1/3 water changed daily (no carbon source addition) and three biofloc groups with glucose, sucrose and molasses addition (limited-exchanged water), respectively. The biofloc volume dynamics in the water showed that carbon addition significantly promoted the biofloc formation in all biofloc groups (P <.05), meanwhile, during the 45day rearing period, biofloc improved water quality by consuming the element N accumulated in the water, then leading to the decrease in the concentration of TAN and NO2--N. However, no significant difference was found in the survival and the growth of prawns between the biofloc groups and the control group (P >.05). Furthermore, the relative gene expression levels of prophenoloxidase (ProPO), catalase (CAT) and superoxide dismutase (SOD) of prawns in the biofloc groups were significantly higher than that in the control group during the acute H2O2 and pH stress (P <.05), as well as the relative gene expression of crustin (CRU) in the biofloc groups was higher than that in the control group during the H2O2 stress (P <.05), which exhibited a stronger adaptive antioxidant and antibacterial response in prawns reared with biofloc, thereby a higher relative percent survival of prawns was recorded in the biofloc groups during pathogen challenge test. Taken together, biofloc system appeared to help prawns to better resist the environment stress.