Virus‐associated spawning papillomatosis in smelt, Osmerus eperlanus L., in the River Thames

Smelt were collected from the R. Thames, at Lots Road Power Station, Fulham between October 1989 to June 1990. Smooth, white, ovoid tumours were observed on the fins of smelt during their anadromous spring migration and recognized as a form of spawning papillomatosis. Papillomatous fish constituted about 21% of the population in March and about 19% in April but were not present in any other samples. Up to 13 tumours were found on a single fish. Papilloma prevalence and intensity were both raised in larger fish. Ultrastructural examination revealed that a high proportion of tumour cells contained virus particles with herpesvirus group characteristics. Epithelial cells of fins without tumours revealed no such virus particles. Evidence of the herpesvirus as a likely aetiological agent of spawning papillomatosis is discussed.