Browsing by Author "Kasai, Akihiro"

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Morphological and molecular genetic characterization of two Kudoa spp., k. musculoliquefaciens, and k. pleurogrammi n. sp. (myxosporea: multivalvulida), causing myoliquefaction Of commercial marine fish
(Springer, 2016-01) Li, Ying-Chun; Mafie, Eliakunda; Sato, Hiroshi; Kasai, Akihiro
Genetic characterization of myxosporean species, including members of the genus Kudoa, has advanced dramat- ically throughout the last decade. This is in stark contrast to those species described further back in time. Kudoa musculoliquefaciens described from the jellied muscle of swordfish, Xiphias gladius, in the western Pacific Ocean off the Sanriku Coast, northern Japan, is one such species. In the present study, multiple pseudocysts (0.66–1.35 mm average length and 0.06–0.10 mm average width) containing K. musculoliquefaciens spores were collected from three host groups: muscle blocks of swordfish caught in the western Pacific Ocean off the Sanriku Coast, or the northern Indian Ocean, and Indo-Pacific sailfish, Istiophorus platypterus, in the western Pacific Ocean off Kochi, western Japan. Subspherical K. musculoliquefaciens spores, 8.0–10.3 μm in width, 7.3–10.0 μm in thickness, 6.4–7.9 μm in sutural thick- ness, and 5.5–8.1 μm in length, had four subspherical polar capsules, 2.8–4.0 μm in length by 2.2–3.2 μm in width. The kudoid spores found in the different host groups showed mor- phometric variations to some extent but had essentially iden- tical nucleotide sequences of the ribosomal RNA gene (rDNA), closest to those of Kudoa hemiscylli or Kudoa carcharhini recorded from elasmobranchs in the Indo-Pacific Ocean. Another kudoid species, Kudoa pleurogrammi n. sp., was recorded from the jellied and normal muscles of Atka mackerel, Pleurogrammus monopterygius and Pleurogrammus azonus, fished in the northern Pacific Ocean or northern Sea of Japan. Subquadrate spores found in round-ended pseudocysts (1.15–3.85 mm in length and 0.11–0.26 mm in width) in myofibers were 8.2–9.1 μm in width, 7.1–8.2 μm in thickness, 5.4–7.7 μm in sutural thick- ness, and 5.6–6.8 μm in length, with four ovoid polar cap- sules, 2.7–2.9 μm in length by 1.4–2.0 μm in width. Kudoid spores from both jellied and normal muscles or different host fish species had identical 18S or 28S rDNA nucleotide se- quences. Thus, molecular genetic characterization of kudoid species with the potential to induce post-mortem myoliquefaction will facilitate the reliable and specific identi- fication of myxosporeans found in either jellied or normal muscles of important commercial fish
New host records of monacanthid fish for three kudoa spp. (k. septempunctata, k. thyrsites, and k. shiomitsui) prevalent In the olive flounder (paralichthys olivaceus), with the description Of k. parathyrsites n. sp. from a black scraper (thamnaconus modestus)
(Springer, 2016) Kasai, Akihiro; Li, Ying-Chun; Mafie, Eliakunda; Sato, Hiroshi
Kudoa septempunctata (Myxosporean: Multivalvulida) is known as a cause of foodborne disease associated with consumption of raw flesh of the olive flounder (Paralichthys olivaceus). Knowledge of its life cycle, particu- larly alternate annelid hosts and reservoirs or susceptible fish hosts in natural waters, may facilitate disease control in aqua- culture farms. Our recent survey of myxosporean infection in monacanthid fish in natural waters around Japan revealed in- fection with three kudoid species prevalent in the olive floun- der, i.e., K. septempunctata, Kudoa thyrsites, and Kudoa shiomitsui. Of the 51 black scrapers (Thamnaconus modestus) examined, five fish were infected: two fish with K. septempunctata and three with K. thyrsites. One of the fish infected with K. septempunctata was also infected with a K. thyrsites-like species. One of the 17 threadsail filefish (Stephanolepis cirrhifer) and two of four unicorn leatherjackets (Aluterus monoceros) were parasitized with K. shiomitsui. Three modest filefish (Thamnaconus modestoides) had no kudoid infection. K. septempunctata from a black scraper fished in the Inland Sea of Japan off Yamaguchi had 6–8 (predominantly 7) shell valves/polar cap- sules, whereas K. septempunctata found in another black scraper from the Sea of Japan off Tottori had 5 or 6 (predominantly 6). However, the two isolates displayed iden- tical 18S and 28S ribosomal RNA gene (rDNA) nucleotide sequences, which were also identical to the isolates from the olive flounder. K. thyrsites from the Inland Sea of Japan off Yamaguchi and Sea of Japan off Tottori and K. shiomitsui from the Sea of Japan off Shimane and western Pacific Ocean off Kochi were also morphologically and genetically characterized. They were found to be coincident with the pre- vious reports from olive flounders. Furthermore, the K. thyrsites-like species found in a black scraper from the Inland Sea of Japan off Yamaguchi was morphologically and genetically characterized; a new species, Kudoa parathyrsites n. sp., is erected for this species. The relation- ships of the new species with K. thyrsites and related species as well as those of K. shiomitsui with Kudoa pericardialis and related species parasitizing the pericardium are briefly discussed.