Abstract: Cryptocaryoniosis is the most serious disease of marine fishes. Cryptocaryoniosis was the most serious disease of marine fishes in Ningde, Fujian. Through continuous monitoring at various stations, extensive investigations and consulting relevant experiments’ data, we mastered the biological features of Cryptocaryon irritans and the prevalence features of Cryptocaryoniosis.The results showed that the occurrence and development of Cryptocaryoniosis were closely related to the environmental conditions, the antecedent factors of which were water stream, depth and cultivation density, and the annual disease trends presented a bimodal shape. The study also confirmed the division method of disease degree. When the water temperature reacheed 22.2℃ in spring, the Cryptocaryon irritans could be seen; when the water temperature reacheeds 23.2℃ to 28.0℃, the disease broke out; when the water temperature dropped to around 27.5℃ in autumn, the disease might also break out. A large number of deaths were due to secondary bacterial infection and hypoxia.