Role of viruses in the induction of skin tumours and tumourlike 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 rnicroscopy and virological methods, virus or virus-hke 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 turnour-inducing viruses, and the possible reasons for seasonal variation in slun tumour prevalence, are revlewed. It is postulated that fundamental principles determne the role of viruses in the induction of skin tumours of fish within a framework of different biological and environmental parameters. KEY WORDS: Fish viruses