ROLE OF VIRUSES IN THE INDUCTION OF SKIN TUMORS AND TUMOR-LIKE PROLIFERATIONS OF FISH

Skin tumours of fish are easily recognizable lesions, some of which have been known for centuries. Causes of fish tumour formation are varied and are often proposed to be multifactorial. In more than half of all cases examined by electron microscopy and virological methods, virus or virus-like particles were found in tumour tissues. So far, oncogenicity has been clearly demonstrated only for herpesviruses isolated from benign tumours. Classification of fish skin tumours, tumour-associated and tumour-inducing viruses, and the possible reasons for seasonal variation in skin tumour prevalence, are reviewed. It is postulated that fundamental principles determine the role of viruses in the induction of skin tumours of fish within a framework of different biological and environmental parameters.