Myxobolus nagaraensis n. sp (Myxozoa: Myxosporea) causes abdominal distension of freshwater goby Rhinogobius sp OR type from the Nagara River

A new myxosporean parasite was found in the body cavity and caudal peduncle of the freshwater goby Rhinogobius sp. Orange type (OR) collected from the Nagara River, Gifu Prefecture, Japan. Infected fish exhibited substantial swelling of the abdomen caused by large parasitic cysts approximately 10 mm in size, formed in the visceral cavity. The cyst was a compacted aggregate of several smaller cysts, similar to a bunch of grapes in appearance. Histological examination showed that plasmodia developed within the renal capsule, and finally occupied the visceral cavity. Spores were ovoid with an attenuated anterior end. Sutural ridges were conspicuous with several folds on the edge. Average spore size was 11.9 (10.5-13.5) mu m long, 9.0 (8.0-10.0) mu m wide, and 6.5 (6.0-7.0) mu m thick. Two equal polar capsules were 5.5 (4.5-6 0) mu m long and 3.0 (2.5-4.0) mu m wide. Partial small subunit ribosomal DNA sequences of the myxosporean were distinct from those of other myxozoan species in GENBANK. A new species name, Myxobolus nagaraensis, is proposed for this parasite.