Background: The giant freshwater prawn (Macrobrachium rosenbergii) is a commercially valuable freshwater crustacean species that is cultivated throughout the world. M. rosenbergii is frequently affected by a variety of diseases. Therefore, feed additive research is necessary to improve the immunity and survival rate of M. rosenbergii. Scutellaria polysaccharide (SPS) extracted from Scutellaria baicalensis (a Chinese medicinal herb) can enhance the antioxidant ability of organisms.
Methods: In this study, M. rosenbergii were fed with 50 mg/kg, 100 mg/kg, and 150 mg/kg of SPS. Following a four-week feeding trial, SPS had no positive effect on the growth of M. rosenbergii compared with the control group. Then, the immunity and antioxidant capacity of M. rosenbergii were tested by qRT-PCR and enzyme activities.
Results: The results showed that the expressions of prophenoloxidase (proPO) and toll receptor (Toll-R) mRNA showed no changes in hemocytes of M. rosenbergii. However, the expressions of heat shock protein 70 (HSP70) and nuclear factor κB (NF-κB) mRNA were up-regulated during the first two weeks of culture and were down-regulated in weeks 3 and 4. The mRNA expressions of HSP70, NF-κB, and Toll-R (participating in the immune response) in heart, muscle, and hepatopancreas were decreased after four weeks of SPS feeding. This indicated that long-term feeding of SPS could regulate the immune responses of M. rosenbergii. The activity levels of antioxidant biomarkers, alkaline phosphatase (ACP), acid phosphatase (AKP), polyphenol oxidase (PPO), catalase (CAT), and superoxide dismutase (SOD), in hemocytes, heart, muscle, and hepatopancreas increased during the feeding time, indicating that the antioxidant capacity of M. rosenbergii was improved by SPS supplementation in the feed.
Conclusions: In summary, SPS was conducive to enhancing the antioxidant capacity of M. rosenbergii. These results provide a theoretical basis in supporting of SPS addition to the feed of M. rosenbergii.