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.
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