Abstract
The histological examination of the spleen of Japanese conger Conger myriaster revealed that there were many eosinophilic island-like structures in splenic hematopoietic tissues, which consisted of large square cells and fibrous structure, when stained with hematoxylin and eosin. Silver stain showed these fibrous structures were composed of abundant reticular fibers that occasionally formed lattice structures. Electron microscopically, these structures consisted of cuboidal endothelial cells, reticular cells, and reticular fibers. In neighboring tissues, there were abundant thrombocytes, lymphoid cells, and macrophages (or monocytes). Basement membranes were poorly developed. When carbon suspensions were injected into the aortic bulb, carbon particles were ingested by macrophages and/or reticular cells in the islands, and were also observed on the bundles of reticular fibers. These data indicate that the eosinophilic island-like structures observed in Japanese conger spleens are well developed splenic ellipsoids, and suggest that such tissues provide a good model for the investigation of trapping foreign antigenic and non-antigenic substances in fish.
