Epitheliocystis in rohu Labeo rohita (Hamilton, 1822) is caused by novel Chlamydiales.
Epitheliocystis, an emerging aquaculture disease, has been reported in >90 fish species from 14 countries. In the present study, we report epitheliocystis from cultured rohu Labeo rohita, an Indian major carp, which is the major cultured species in the Indian subcontinent. The affected fish exhibited lethargy, swimming near the water surface followed by mortality. In wet mounts of gills, infestation with dactylogyrids, trichodinids and myxosporeans was observed. Subsequently, following euthanasia, the affected fish were dissected and subjected to routine bacteriological, virological and histopathological investigations. The bacteria could not be isolated from internal organs, namely kidney and liver. In addition, cytopathic effects were not observed in the Cyprinus carpio koi fin (CCKF) cell line following inoculation of filtered tissue homogenate from pooled kidney samples. In histology of gill sections, amorphous intracytoplasmic inclusions typical of epitheliocystis were observed in epithelial cells, and the presence of chlamydial DNA in gills was confirmed by amplification of 16S rRNA gene sequence of Chlamydiales. The sequencing of amplicons (774 bp) revealed that the epitheliocystis agents from rohu belong to family Candidatus Parilichlamydiaceae in the order Chlamydiales. Since the sequences of epitheliocystis agent from rohu showed <95% similarity with any member of the genera in above family, therefore, these agents appear to be novel, and it is proposed that these may be known as Candidatus Panilichalamydia rohitae. Using in-situ hybridisation, the 16S rRNA gene amplicons labelled with digoxigenin, linked to the epitheliocysts. The present study adds to the growing range of host species affected by epitheliocystis.