What causes the abdominal tumours in koi? What is the tumour? Is it caused by a virus?

For years, my clients and I have been coming across huge tumours that take over the coelomic cavity of these beautiful fish. Some may be small enough to surgically remove without too many troubles. However, some are so invasive that fish have to he euthanased when we see the extent on exploration.

Work done by Assoc. prof. Yasumoto and his team have characterised the tumour to be neoplastic (cancerous), malignant, of gonad (reproductive organ) origin. The name for it is, undifferentiated gonadal carcinoma.

More prevalent in females, but present also in males. To date, no viruses have been found. He suspect that it is hereditary (i.e. passes down from parents to offspring).

So, this confirms my suspicions. I see many with only ever single fish affected from geographically isolated populations. This supports a non-infectious cause.

But what about chemical exposure?
Formaldehyde and malachite green are known tumour-inducers in mammals. Repeated exposure is likely because they are frequently used for prophylactic antiparasitic and antifungal treatments. There are, however, no reports of tumour induction by these chemicals in fish.

Food for thought.


Yours sincerely,

Dr Richmond Loh 

DipProjMgt, BSc, BVMS, MPhil (Pathology), MANZCVS (Aquatics& Pathobiology), CertAqV, NATA Signatory.
THE FISH VET, Perth, Western Australia, AUSTRALIA. 

Mobile Aquatic Veterinary Medical & Diagnostic Services.
Ph: +61 (0)421 822 383

4 thoughts on “What causes the abdominal tumours in koi? What is the tumour? Is it caused by a virus?

  1. Really interested in the article on tumours in koi. I routinely examine fish for movement consent in the UK and these tumours also occur very frequently in female carp.


  2. hi Richmond,
    i have a male doitsu platinum and have owned him from .70mm, he is now 80cm!, he has had a weird body shape since about 20cm and has never lost appetite or lost interest in the rest of the group, now the bumps have evened out but looking like they have shifted towards the anal vent,some people reckon he is going to die but not sure obviously,if he does i would like to employ your services and find out what is the problem/cause.
    thanks for your dedication to helping us koi/fish keepers understand whats going on with the other side of our hobby learning.
    Constantino Pismiris.


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