Ultrastructural studies on fish microsporidians

Abstract

During our studies of fish microsporidia, we have been lucky enough to encounter the three genera which occur most commonly in fish; Glugea, Loma and Pleistophora. All form whitish nodules containing vegetative and spore-forming stages of the parasite. In Glugea and Loma these stages are contained within a hypertrophied host cell. In Glugea most of the vegetative stages are at the periphery of the nodule, and groups of 16 spores form in sporophorous vesicles limited by thin membranes. In Loma vegetative and spore-forming stages are mixed in the nodules, and only 1-2 spores are found in each sporophorous vesicle. In Pleistophora the stages are again mixed, with large groups of spores forming in sporophorous vesicles each surrounded by a thick pansporoblast membrane which persists in squash preparations, so that the spores appear to be in “packets”. The nodules are often surrounded by host fibroblasts, and are sometimes invaded by macrophages.