Histology and Prevalence of X-Cell Lesions in Atlantic Cod (Gadus morhua)

The prevalence of X-cell lesions in Atlantic cod (Gadus morhua) from the Canadian Atlantic was similar to that in German Bight and lower than their prevalence in G. macrocephalus off the west coast of Canada. The lesions, which are now believed to be xenomas composed of X-cell parasites and host cells were different from those described by other authors in that the pseudobranchs could always be seen on the exposed surface of the lesion, and were not infiltrated by X-cells. Sometimes the X-cell lesion was separate from the pseudobranch. Most of the X-cells in the lesion appeared to be degenerate, but areas of normal X-cells with distinctive features could always be found. No phagocytes were seen in the X-cell lesion, although a cellular host reaction to microsporidian and other parasites was often seen in and around the pseudobranch. It is suggested that the envelope cells, which are fibroblast-like, may represent a host response to the X-cells.Key words: pseudobranch tumor, X-cells, Atlantic cod, Gadus mo...