Cryptocarioniasis, which is caused by , is difficult to control in cultured large yellow croaker, and dozens of other marine fish species and is seriously threatening development of the aquaculture industry. To investigate the effects of the Chinese herbal compound (HD-2)[Dryopteris crassirhizoma, (Burm. f.) Nees] for treating cryptocarioniasis, were collected and fed different doses of HD-2 to compare changes in non-specific immune indices, such as lysozyme (LZM), total superoxide dismutase(T-SOD), alkaline phosphatase (AKP), and acidic phosphatase (ACP) activities. The results showed that HD-2 promoted LZM, T-SOD, AKP, and ACP activities, and maximum activities were observed 14-21 d after feeding 2% HD-2. No . However, 20%, 54%, and 89% of the theronts were killed at concentrations of 80 mg/L, 100 mg/L, and 200 mg/L HD-2, respectively; all theronts were killed by 400 mg/L HD-2. The median lethal concentration for 50% (LC₅₀) of the theronts was 109 mg/L. A 15-d indoor therapeutic experiment was performed in which fish were assigned randomly into groups A-C and a control. Fish in group A had a survival rate of 50% after being fed 20 g/kg HD-2 in feed and dipped in a 100 mg/L HD-2 bath. Fish in group B had a survival rate of 50.67% after being fed 20 g/kg HD-2 in feed and dipped in a 50 mg/L HD-2 bath. Fish in group C achieved a survival rate of 42.67% after being fed 20 g/kg HD-2 in feed. The survival rates of the three treatment groups were significantly higher than that of the control group (2.67%). The number of trophontson the pectoral fins of was significantly lower than that in the control group. The number of trophonts on gill filaments declined during the three treatments. In contrast, the number of trophonts in the control group increased significantly, where as the number of tomonts in the treated groups decreased significantly. The numbers of tomonts in groups A, B, and C decreased by 100%, 91.1%, and 77.7%, respectively, on day 12 and were significantly different from those in the control group. In conclusion, simultaneous oral administration and a medicated bath in HD-2 was the most efficacious treatment for cryptocarioniasis. The 2% HD-2 oral treatment added to feed for 6-14 d is recommended to guarantee higher survival rates of based on availability and cost considerations. These results provide a theoretical reference and technical support for preventing and controlling cryptocarioniasis, and will be useful for fish culture in future.