Studies on Glugea Infection of the Ayu, Plecoglossus altivelis—I

Abstract

A new species of microsporidian parasite of the ayu, Plecoglossus altivelis T. & S., is described and the name Glugea plecoglossi n. sp. is suggested.In a heavy infection of the parasite xenomas develop in large number in various organs, viz., peritoneum, visceral cavity, ovaries, testis, fat body, pyloric caeca, spleen, muscle, liver, heart, gills, iris, etc., and cause serious damage to fish. The xenomas are variable in size, being 0.5-3 mm, rarely as large as 5 mm.Fresh spores of the parasite are elongate or ellipsoidal and are 5.1-6.2×2.0-2.5μ, the average of 200 spores being 5.8×2.1μ Spores fixed in Bouin's solution and stained with Heidenhein's iron hematoxylin are 3.8-4.8×1.5-2.0μ, the average of 50 spores being 4.0×1.8μ. Everted filaments are 180μ at maximum, being 100-150μ in the majority.The processes of schizogony and sporogony of the parasite studied with artificially infected ayu are in substance the same as those reported by WEISSENBERG (1968) on Glugea anomala and by SPRAGUE and VERNICK (1968) on G. weissenbergi. A very small xenoma of 4×8μ with a single schizont and a single host cell nucleus was found in the lamina propria of the villi of the gut of an ayu killed 5 days after infection. Sporonts in smear preparations of parasite are 3×4μ and each sporont produce two spores. Therefore the parasite is classified into the genus Glugea.Inoculation experiments have shown that Salmo gairdneri is susceptible to the parasite, but Gasterosteus acelatus microcephalus is unsusceptible.Of about 15 species of Glugea in fish, G. hertwigi has spores similar in size to those of the present Glugea. But the former differs from the latter in the following points. The hosts of G. hertwigi are Osmerus mordax and O. eperlanus and it has been reported by WEISSENBERG (1968) that Gasterosteus aceleatus is susceptible to G. hertwigi. G. anomala and G. weissenbergi are distinguishable in having smaller spores, 3-6×1.5-2μ, and larger spores, 6.0-7.0×2.5-3.6μ, respectively, and in having different hosts, the sticklebacks. G. takedai which was found in the rainbow trout in Japan is distinguishable in having smaller spores, 2.8-4.9×1.7-2.3μ, and in not causing hypertrophy of the infected host cells.