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.

The occurrence of 2 helminths is reported in eel from 3 regions of the Federal Repubhc of Germany Both specles, Angudhcola crassus (Nematoda Dracunculoldea) and Paratenuisentis ambjguus (Acanthocephala, Tenuisentidae) were recently lntroduced Into Europe, probably from Japan and the USA, respecbvely The morphology of A crassus differs from the onglnal descript~on In a few features Syntype speclmens from Japan however, showed that speclmens from Japan and from Germany are conspecif~c The morphology of P ainbiguus (flrst report from Europe) corresponds xvell

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