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Eye lesions in koi

The lesions shown here are not unique to koi but highlight the range and severity of eye diseases in fish. Careful examination is required, often with magnification and usually with the fish anaesthetised and removed from the water. Many lesions are subtle in the early stage of the disease but are generally advanced by the time they are presented for treatment. Their appearance can reflect some of the many different causes that can be due to poor water quality, physical injury, tumours or diseases due to parasites, bacteria or viruses. The underlying cause determines the course of action or treatment and severe cases often require enucleation.

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