Enhancing the immune response in the sea cucumber Apostichopus japonicus by addition of Chinese herbs Houttuynia cordata Thunb as a food supplement

The Chinese herb Houttuynia cordata Thunb (abbreviated as HCT hereafter) has been widely used in human and livestock medical research. However, few studies have tested the effects of HCT in aquaculture systems, particularly in echinoderms. In this study, the impact of HCT was evaluated when used as a feed additive to enhance the immune response of the sea cucumber, Apostichopus japonicus. Two concentrations, 1.5% and 3%, of HCT powder were tested by adding them to the feed. Feeding experiments had a four week duration and each week, the humoral and cellular immunity index of the intestine, tentacles, peristome, and coelomic fluid were analyzed. The results indicated that the percentage of A. japonicus coelomocytes significantly increased after supplementing feed with HCT, and reached a peak after one week of feeding with the 3% HCT supplementation. Analysis of reactive oxygen species (ROS) indicated that HCT in feed caused a notable increase in the coelomocyte ROS concentrations over the experimental period. In both the 1.5% and 3% HCT addition groups, the ROS peaked in the third week and then remained stable. In addition, alkaline phosphatase, acid phosphatase, superoxide dismutase, lysozyme activity of the intestine, tentacles, peristome and coelomic fluid were significantly improved during the four-week test period. In conclusion, 1.5% and 3% HCT added to feed boosts the immune responses of A. japonicus. HCT has potential as an immune enhancer for mariculture of sea cucumbers.