DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03728

ABSTRACT: Silver pomfret Pampus argenteus is a major cultivated marine fish species with a high market value. In the summer of 2021, Cryptocaryon irritans, a ciliate parasite, infected the cultured silver pomfret in the aquaculture ponds of Ningbo, Zhejiang, China. The symptoms of infected fish include white spots on the skin and fins, increased body surface mucus, loss of appetite, irritability, and shedding of scales. After collecting white spots from moribund fish, the 18S ribosomal RNA sequence of the pathogen on the fish skin was amplifed by PCR: phylogenetic analysis showed that it was closely related to C. irritans strains from Ningde, Fujian, China. In the present study, 4 groups were tested in an artificial infection experiment over the course of 72 h, consisting of 3 infected groups (1600, 4000, and 8000 theronts fish^–1) and one healthy group. White spots were observed on the skin and fins of the infected fish, but not on their gills. Samples were taken from the gills, liver, kidney, and spleen of both infected and healthy fish and were compared to find significant histopathological differences from the healthy fish. As the dose of infection increased, the symptoms became more pronounced. At 72 h, the mortality rates were 8.3, 50, and 66.7% for the 3 different concentrations, respectively. The LC₅₀ was calculated to be 366 theronts g^–1 at 72 h, 298 theronts g^–1 at 84 h and 219 theronts g^–1 at 96 h. This study emphasizes the importance of developing early diagnosis methods and appropriate prevention strategies to decrease the impact of C. irritans infection in silver pomfret aquaculture industry.