The susceptibility of eight marine fish species cultured in South China were tested for infection by the parasitic ciliate, Cryptocaryon irritans, via a challenge examination and an immobilization assay.All species of fish (representing six different families) that we investigated were infected by C.irritans except the rabbitfish (Siganus oramin), which displayed resistance to C.irritans infection.The infection intensity of rabbitfish (0.92±0.969, p<0.05) was significantly lower while the immobilization titres of rabbitfish serum were significantly higher (44.51±22.982 p<0.05) than the other seven species of fish.