Received: Jul 18, 2025 / Accepted: Oct 01, 2025 / Published: Dec 31, 2025
Cryptocaryon irritans is an ectoparasitic protozoan responsible for white spot disease, posing a significant threat to mariculture systems in Vietnam. This study aimed to isolate and propagate C. irritans, and to establish an experimental infection model in Trachinotus spp. (5-7cm in length) under laboratory conditions. Between February and June 2025, a total of 106 fish samples were sourced from aquaculture operations in Quang Ninh and Khanh Hoa, revealing an average C. irritans infection rate of 59.43%, with the highest prevalence observed during March and April. Infected fish exhibited clinical signs including skin darkening, mucus loss, white spots on the skin and gills, fin erosion, ulcerations, and tissue damage. The parasite was successfully cultured at the trophont stage and was propagated to the tomont and theront stages at 28-30°C, achieving a conversion efficiency of 61.7% after 48 hours and yielding an average of 150-300 theronts per tomont. These theronts were introduced to Trachinotus spp. at a density of 5,000 theronts per 250L tank (50 fish) at a temperature of 28°C. The infection progressed rapidly, with trophonts observed within 2-3 days and cumulative mortality reaching 100% by day seven. The established infection model offers a robust platform for further research in epidemiology, immunology, and therapeutic interventions against C. irritans.
