Osteitis deformans in koi

This rare disease produces dramatic changes to the bones of the spine in koi. Other species may be affected but I have only seen this in four cases in my long career. Affected fish may show some degree of spinal stiffness with reduced flexing and more exaggerated swimming motion of the pectoral fins. The disease is usually found coincidentally on X-rays when looking for other health problems. The underlying cause is not known but it has similarities to Paget's Disease in humans and other animals. There is no known treatment. Click here for a report of cases in Australia.

X-ray of affected koi
X-ray of affected koi

This 10 year old koi had a slightly stunted body with reduced flexibility of its spine when anaesthetised. It had some stiffness when swimming and redness of its tail but was otherwise healthy. The bones of the entire spine are deformed, with compression along its length and upward deviation (lordosis) near the tail.

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Defleshed spine of a severely affected koi
Defleshed spine of a severely affected koi

The muscle and soft tissues have been removed to reveal the extent of the disease in this 6 year old koi. The fish had been unwell for 3 months with marked stiffness and difficulty swimming, and was unable to maintain its buoyancy. All the bones of the spine are severely affected by the disease, but it was other unrelated internal problems that caused a deterioration in its health.

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Close-up side view of affected vertebrae
Close-up side view of affected vertebrae

The irregular nodular edges of the vertebrae are clearly visible adjacent to the yellow remnants of the ligaments. These nodules are thought to be deposits of new bone, which is part of the disease process, although the underlying cause remains unknown.

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X-ray of affected koi
X-ray of affected koi

This 10 year old koi had a slightly stunted body with reduced flexibility of its spine when anaesthetised. It had some stiffness when swimming and redness of its tail but was otherwise healthy. The bones of the entire spine are deformed, with compression along its length and upward deviation (lordosis) near the tail.

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