Cysts of unknown etiology in marine fishes of the Northwest Atlantic and Gulf of Mexico

Results of light and electron microscopic examinations of cysts of unknown etiology (CUEs) occurring in the gills of Atlantic mackerel, red hake, white hake, cod, haddock, and silver hake are presented. CUEs were found also in gills and viscera of winter flounder, Atlantic croaker, spot, windowpane flounder, and sand lance. CUEs measured 150–400 μm in diameter and consisted of an external fibrous cuticle, usually a thick median band, and a central core that frequently contained eosinophilic vesicles. Structures resembling mitochondria were found in the band and in vesicles of the core, but no other organelles were apparent. Cytochemical staining and ultramicroscopy revealed aggregates of glycogen in the core ground substance; no structural components were stained with Sudan black B or by the Feulgen technique. Extensive encapsulation of CUEs by fibroblasts was typical. Of 717 mackerel examined, 76.8% had CUEs in the gills; numbers ranged from 1 to 353 per fish. The prevalence and intensity of occurrence o...