Houttuynia cordata Thunb (HCT) has been widely used as traditional Chinese medicine in human and livestock for its antiviral and antibacterial activities. In this study we are investigating the effect of HCT in aquaculture animals. In this study, 300 olive flounders (Paralichthys olivaceus) were stochastically divided into four experimental groups: basal diet feeding group, 0.5% HCT continuous feeding group, 1% HCT feeding group, and 1% HCT interval feeding group. Three replicates were set for each treatment, and 25 fish were stocked on each replicate. The results of continuous feeding experiments showed that the continuous addition of 0.5% and 1% HCT feed for 28 days could very markedly increase peripheral leukocytes count, serum lysozyme activity, phagocytic rate, phagocytic index, respiratory burst activity of head kidney cells, compared with the basal feed group (P<0.05 or P<0.01). The challenge test results also showed that the 0.5% and 1% HCT feeding had higher immune protection against Edwarsiella tarda infection; and the relative protection ratios were 60% and 50%, respectively. It was also obtained that interval feeding experiments also significantly boost non-specific immunological function of P. olivaceus compared with continues feeding experiments, HCT application in P. olivaceus farming potentially enhances P. olivaceus resistance against E. tarda infection.
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