Internal tumours in koi

Koi and other carp commonly develop internal tumours, often from 4years of age. These usually develop in the liver or gonad (ovary/testes), but in many the cells are hard to identify and are called a sarcoma. They often cause swelling of the belly with lethargy and progressive loss of appetite and other complications over the following weeks or months. A physical examination and palpation of the swelling may reveal areas of an irregular solid mass internally. This can be confirmed by X-ray or using an ultrasound scan, but most are inoperable, and the outlook is usually hopeless.

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Extensive swelling of the belly
Extensive swelling of the belly

This 12year old koi developed progressive swelling for over a year, before becoming seriously ill. Half of its final bodyweight was due to free fluid in the body cavity along with two large cystic tumours.

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Localised swelling of the belly
Localised swelling of the belly

This adult koi had a more localised swelling of the body cavity due to a discrete solid internal tumour. Although this was visible when the fish was examined under an anaesthetic, simple physical palpation of the belly confirmed its presence.

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Post mortem of a koi with an internal tumour
Post mortem of a koi with an internal tumour

This adult koi had progressive swelling of the belly for 6months. In addition to the large solid liver tumour (black asterisk), the twin-lobed sacks of the ovary (white asterisks) were filled with abnormal translucent yellow fluid.

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Extensive swelling of the belly
Extensive swelling of the belly

This 12year old koi developed progressive swelling for over a year, before becoming seriously ill. Half of its final bodyweight was due to free fluid in the body cavity along with two large cystic tumours.

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