Parasite	Loma sp. (Loma salmonae ?)
Taxonomy	Microspora, Microsporea
Host	Red spotted masu salmon (Oncorhyncus masou)
Disease name	Microsporidial gill disease
Infection site	Gill
Clinical signs	Many spherical xenomas (a complex formed by a host cell and a parasite) are observed in the gill (Figs. 1, 2).
Parasitology	A number of spores are produced inside the xenomas (Fig. 3). A spore (average length 4.5 mm; average width 2.3 mm) is pyriform.
Pathology	The gill filaments were swollen and clubbing.
Health hazard	Since this parasite is not infectious to human, it is harmless in food hygiene.
Diagnosis	Check the spores by the wet-mount of xenomas. The sample should be smeared and stained by Uvitex 2B followed by a fluorescent microscopic observation. The stained spores emit blue fluorescence under UV radiation.
Other information	Loma salmonae is well known species because it causes heavy damage to the culture of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch in North America. In Japan, Loma salmonae-like species was reported in masu salmon O. masou, but this microsporidium is not identified to the species level. (Awakura et al., 1982). Likewise, Loma sp. in red spotted masu salmon is not identified as Loma salmonae despite its morphological similarities.
References	Awakura, T., M. Tanaka and M. Yoshimizu (1982): Studies on parasites of masu salmon, Oncorhynchus masou- IV Loma sp. (Protozoa: Microsporea) found in the gills. Sci. Rep. Hokkaido Fish Hatchery, 37, 49-55.

Fig. 3. Fresh spores of Loma sp.

(Photos by H. Aoshima (1, 2))

Fig. 1. Numerous xenomas formed in the gill filament.

Fig. 2. Xenomas of Loma sp.