Lentivirus-like particles in connective tissue tumours of fish from German coastal waters

Abstract

A conspicuous yellow tumour was found for the first time in January 1989 among hooknose Agonus cataphractus collected from different parts of the German Wadden Sea. Prevalence of the tumour was 0.7 %. The tumours arose from connective tissue and were classified as fibromas or possibly fibrosarcomas Electron microscopy revealed the presence of lentiwus-like particles within cytoplasmic vacuoles of tumour cells. This is the first report of a lentivirus in a lower vertebrate or from an animal residing in the aquatic environment. Since the first large-scale surveys of marine fish for diseases in 1968 in Californian waters (Cooper & Keller 1969) and 1970 in the Irish Sea (Perkins et al. 1972), concern has been expressed that the health of wild fish might be affected by anthropogenic wastes disposed into coastal waters. As a result, many additional surveys have been conducted, mainly covering coastal waters of North America and western Europe (Mix 1986, Moller & Anders 1986). Those studies conducted in the North Sea area, where intergovernmental approaches to monitor pollution effects include disease surveys, have focussed particularly on flatfish. One of the more recent surveys in 1988-89 covered the German Wadden Sea, the shallow, sandy-muddy coastal zone between the borders to Denmark in the north and The Netherlands in the west (Moller & Anders in press). That survey, and a pilot study in the neighbouring Elbe estuary from 1981 to 1986, revealed a number of 'new' fish diseases, such as the food-induced buccal granulomatosis of smelt Osmerus eperlanus (Anders & Moller 1987), spawning papillomatosis of smelt which is linked with a herpesvirus infection (Anders 1989b), and 'yellow pest' of cod iInter-Research/Printed In Germany Gadus morhua, probably induced by a CytophagaFlexibacter-like bacterium (Hilger et al. 1991). During the Wadden Sea survey, tumours were reported from hooknose Agonus cataphractus for the first t ~ m e . This bottom-fish specles is distributed from the White Sea to northern France, and from Iceland to the western Baltic. In the Wadden Sea, it is one of the most abundant by-catch species in the local trawl fishery for brown shrimp Crangon crangon. The population biology of the hooknose is largely unknown, but young stages of about 2 cm total body length occur in catches from May onward. Adults rarely grow larger than 17 cm in the Wadden Sea, where they mainly feed on brown shrimp. Among 1653 fish examined, 11 tumour-carrying individuals were found. In 6 fish, tumours of a distinct yellow colour were found. In other fish, the tumours were skin-coloured (black to reddish). Two specimens each had 1 tumour of both types (Fig. 1). The first tumour of this kind was found in January 1989 and was not observed the previous year. Independently, local fishermen reported seeing the yellow tumour type for the first time in April 1990, after having caught several conspicuously affected fish with tumours on their heads in the Wadden Sea near the isle of Amrum. The 7 tumours histologically studied ranged from 3 to 9 mm in diameter and represented both globular and flat forms. Based on histological evaluation, 6 of the tumours were preliminarily classified a s benign and arising from connective tissue, thus representing fibromas. In one case, a tendency of tumour cells to invade muscular tissue was observed. Based on histological characteristics, the tumours could be grouped 152 Dis. aquat. Org. 11. 151-154, 1991 Fig. 1. Agonus cataphractus. A hooknose from the German Wadden Sea, bearing 2 conspicuous tumours (arrows) on the body surface. Scale shown is in cm into 2 types corresponding to their colour. Skin-coloured tumours displayed slightly proliferated epidermal layers, an intact basal lamina, strong proliferation of connective tissue cells which were well interlaced with bundles of collagen, and a more or less strong vascularization of the tumour tissue. The 2 yellow tumours examined differed from the others in that they had additionally a high abundance of immune cells (e.g. lymphocytes and granulocytes), as well as several multi-nucleated giant cells, within the proliferative