William H Wildgoose MRCVS
Pet fish vet
Papillomas in koi
Papillomas are non-malignant tumours of the skin and vary in appearance from flat, smooth lumps to large masses with a rough lumpy surface. They can be solitary lesions or there may be several, which coalesce over a large area. Carp pox is also a papilloma, which typically affects koi and carp, but may also affect several tropical fish species. It is caused by a virus, cyprinid herpesvirus 1, and produces a harmless smooth growth on the skin that looks like a drop of white, molten candle wax.
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There are often multiple lesions on the same fish. It was often thought to affect carp more in cold weather but now appears at any time of the year, regardless of the water temperature, and the lesions often disappear and regrow with equal irregularity.
This disease commonly appears as solitary lesions on the body or fins of affected fish. It rarely causes any harm to the fish and often disappears on its own over several months without the need for any treatment.
This koi had papillomas and skin thickening, but also had a large, ulcerated mass in the gill space. It was identified as a squamous cell carcinoma, a malignant tumour, which was thought to have developed from a papilloma.
There are often multiple lesions on the same fish. It was often thought to affect carp more in cold weather but now appears at any time of the year, regardless of the water temperature, and the lesions often disappear and regrow with equal irregularity.