William H Wildgoose MRCVS
Pet fish vet
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.
This young koi had a bacterial septicaemia that caused severe skin ulcers and inflammation of the body in addition to the blood in the anterior chamber of both eyes. Usually, it is seen as a pool in the lower part of the chamber. If the bacterial disease is treated effectively, the blood will be reabsorbed. Physical trauma can result in similar bleeding.
It is not uncommon for koi have pigmentation in the upper half of the cornea, often similar in colour to the surrounding skin. Equally, haze may develop and reduces the transparency of the cornea. This may be due to physical injury or disease but is also thought to be a natural protection against solar light or glare. Early stages of some eye diseases and healing can also have a similar appearance.
The tumour tissue appeared to mushroom out of the enlarged eyeball but did not invade into the surrounding tissues. Much of the exposed surface showed signs of healing despite the erupting mass. The fish survived for several months with no real change in appearance but died following a pond pump failure.
This young koi had a bacterial septicaemia that caused severe skin ulcers and inflammation of the body in addition to the blood in the anterior chamber of both eyes. Usually, it is seen as a pool in the lower part of the chamber. If the bacterial disease is treated effectively, the blood will be reabsorbed. Physical trauma can result in similar bleeding.