X-cell disease of cod Gadus morhua from the North Sea and Icelandic waters

Abstract

Tumour-like swellings in the pseudobranchial region have been described to occur in gadidae of many marine areas. They are associated with the presence of X-cells of unknown origin. Their occurrence in cod Gadus morhua L. in the North Sea has regularly been studied since 1982, and additionally from 1991 to 1993 in Icelandic nearshore waters. Histologically, the lesions found in Icelandic cod were identical to those previously described for North Sea cod. In Icelandic cod, lytic or disintegrating stages were more frequent than previously described For the North Sea, a considerable long-term variability of the prevalence of X-cell disease in cod was recorded ranging from O to 4.6%, with a maximum in January 1989. The variability was different in different areas of the North Sea, and was compared with the fluctuations of numbers of cod caught per hour. Lengths of cod afflicted with the disease in the North Sea do not normally exceed 40 to 50 cm (predominantly age classes II and III are affected). No such restriction was found in Icelandic waters where cod up to 100 cm length were found to be affected. In Icelandic waters, affected fishes were significantly smaller than their healthy compatriots at a given age. There was no density dependence for the infestation of cod in the material tested for the North Sea. There is a need for further studies on the impact of the disease on the growth of cod, and the etiology of X-cell diseases needs to be elucidated.