DAO 83:77-84 (2009)  -  DOI: https://doi.org/10.3354/dao01985

ABSTRACT: Allogynogenetic crucian carp Carassius auratus gibelio (♀) × Cyprinus carpio var. singuonensis (♂) is one of the main freshwater aquaculture species in China. In recent years, epidermal papillomas have been observed on the scales, fins and opercula of adult fish in many fish farms in the Chongming county of Shanghai, China. The disease appears in the late autumn of the first year and becomes more severe in winter. It gradually regresses in the late spring or summer of the second year, as water temperature increases. Our study revealed that the disease pathogen was likely to be a herpes-like virus, as indicated by enveloped viral particles in the cytoplasm, empty capsids in the nucleus and a virus-like morphology of the pathogen. The size of the enveloped herpes-like virus was 118.18 ± 10.53 (SD) nm (n = 22) and its nucleocapsid was 78.64 ± 7.74 nm (n = 22) in diameter. Histopathological examination of tumours revealed that both epithelial and stromal cells proliferated to form papillomas. The nuclei of epithelial tumour cells were irregular in shape and in size. Most of the mucous cells were located in clusters near the middle of each papilloma. Cytoplasmic organelles were sparse in tumour cells. Numerous granulocytes and lymphocytes infiltrated into the tumour tissue. There were no inclusion bodies in the cytoplasm and nuclei of tumour cells. The lesions only occurred in adult allogynogenetic crucian carp, even though they were cultured together with other fish species. There was marked variation in incidence: in some ponds, only a few fish were affected, while the incidence was up to 90% in other ponds.

KEY WORDS: Epidermal papilloma · Histopathology · Etiology · Herpes-like virus · Carassius auratus gibelio (♀) × Cyprinus carpio var. singuonensis (♂)