DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03672

ABSTRACT: Epitheliocystis, is an emerging and global aquaculture disease caused by a diverse range of bacteria of the order Chlamydiales. The present study reports a case of epitheliocystis caused by a novel Chlamydia bacterium, which related to 40% mortality in cultured Spinibarbus denticulatus. The affected fish exhibited lethargy, were observed swimming near the oxygen pump and subsequently died. Histopathology analysis revealed that lesions were concentrated mainly on the gills. The epithelial cells of the damaged gill lamellae hyperplasia, fusion and adhesion, and characterized by inflammation and necrosis. Inclusion bodies were observed in some proliferating epithelial cells at the tips of the gill lamellae. In addition, accompanied by different degrees of mucous cell proliferation. The TEM examination clearly showed the morphological characteristics of chlamydia-like bacteria in epithelial cells. In addition, 16S rRNA sequencing (752 bp) and molecular phylogenetic analyses revealed that epitheliocystis agents detected in S. denticulatus belonged to a novel Chlamydiaceae family. This is the first report of epitheliocystis in cultured fish in China, and the findings in this study increased the range of hosts affected by epitheliocystis.