Abstract
We investigated mass mortalities of koi, C yprinus carpio L innaeus, 1758, experienced in South Indian fish farms by virus isolation, electron microscopy, PCR detection, sequencing of capsid protein gene and transmission studies. Samples of moribund koi brought to the laboratory suffered continuous mortality exhibiting swimming abnormalities, intermittent surfacing and skin darkening. Irido‐like virus was isolated from the infected fish in the indigenous snakehead kidney cell line ( SNKD 2a). Icosahedral virus particles of 100 to 120 nm were observed in the infected cell cultures, budding from the cell membrane. Virus transmission and pathogenicity studies revealed that horizontal transmission occurred associated with mortality. PCR analysis of infected fish and cell cultures confirmed the presence of R anavirus capsid protein sequences. Sequence analysis of the major capsid protein gene showed an identity of 99.9% to that of largemouth bass virus isolated from N orth A merica. Detection and successful isolation of this viral agent becomes the first record of isolation of a virus resembling S antee– C ooper R anavirus from a koi and from India. We propose the name koi ranavirus to this agent.