Approximately three dozen Myxobolus spp. (Myxozoa: Myxosporea: Bivalvulida) have been described to parasitize the gills of carp of the genera Cyprinus and Carassius. Hitherto, these fish were often introduced to temperate waters worldwide as food and ornamental fish from Asia, their place of origin. The present study examined the myxosporean infection of seven common carp (Cyprinus carpio) and seven Japanese silver crucian carp (Carassius langsdorfii) collected from the Fushinogawa River around the university in Yamaguchi City, Japan, during the period April 2015 to October 2016. In total, four Myxobolus spp. were detected in the gill lamellae of Cy. carpio and Ca. langsdorfii, i.e., two species in each species of fish. The four species were characterized morphologically and genetically based on the 18S ribosomal RNA gene (rDNA). A new species, Myxobolus tanakai n. sp., from four individuals of Cy. carpio had an elongated pyriform spore (15.4-18.6 μm by 6.3-8.4 μm), resembling the spore shape of Myxobolus koi from Cy. carpio or Carassius auratus in Japan, China, and the USA, but bigger than it (13.2-15.6 μm by 6.6-7.8 μm). The new species formed a clade with M. koi but was distinct from any of the isolates of this species (nucleotide identities less than 98.6%). The second new species, Myxobolus paratoyamai n. sp., from a single Cy. carpio with its one prominent and one rudimentary polar capsule closely resembled the spore morphology of Myxobolus toyamai from Cy. carpio or Carassius gibelio in Japan, China, and the USA. However, the isolate formed a clade with Myxobolus longisporus from Cy. rubrofuscus in China rather than with M. toyamai isolates (nucleotide identities less than 97.9% with known species). Another new species, Myxobolus ginbuna n. sp., from two individuals of Ca. langsdorfii had similar-shaped spores to Myxobolus wulii, but the dimensions were smaller (11.7-13.9 μm by 8.5-9.8 μm vs. 17.6-18.5 μm by 8.9-10.0 μm). This new species formed a clade with M. wulii but was distinct from any of the M. wulii isolates from Ca. gibelio in China (nucleotide identities less than 99.1%). An additional species, Myxobolus pyramidis, from six individuals of Ca. langsdorfii was morphologically and genetically similar to the previous record from Ca. gibelio in China (99.6% nucleotide identity of the 18S rDNA). Two of these six individuals were mix-infected with M. ginbuna n. sp. This is a new host and geographical distribution record for M. pyramidis.
The Japanese Spanish mackerel (Scomberomorus niphonius; Perciformes: Scombridae) is widely distributed in the continental shelves of the northwestern Pacific Ocean around Japan, Sea of Japan, and East China Sea. In the present study, small, spindle-shaped myxosporean plasmodia (0.15-0.53 mm by 0.04-0.13 mm) were frequently encountered in the myofiber of trunk muscles of two Japanese Spanish mackerels; one fished in the Sea of Japan off western Japan and the other in the northwestern Pacific Ocean off southern Japan in the autumn of 2016. Isolated myxospores of Kudoa konishiae n. sp. (Myxosporea: Multivalvulida) from these two fish were stellate with six equal shell valves and polar capsules, 8.1-9.7 μm in width, 7.1-8.8 μm in thickness, and 7.1-8.8 μm in length. The polar capsules were teardrop-shaped, 2.7-4.7 μm by 1.2-2.5 μm. The lateral view of spores revealed a drawstring-pouch shape. The nucleotide sequences of the 18S and 28S ribosomal RNA gene (rDNA) were distinct from any recorded species. Phylogenetic trees demonstrated a close relationship of the present new species with Kudoa spp. with stellate spores with five or more shell valves/polar capsules, recorded in scombrid fishes. To clarify the phylogenetic relationships between three closely related species, i.e., Kudoa konishiae n. sp., Kudoa hexapunctata, and Kudoa neothunni, three mitochondrial DNA genes (cytochrome c oxidase subunit 1 gene (cox-1) and the small and large subunits of the ribosomal RNA gene (rns-rnl)) of two isolates of the new species, six isolates of K. hexapunctata, and 13 isolates of K. neothunni were sequenced. The interspecific and intraspecific variations of the newly obtained cox-1 and rns-rnl nucleotide sequences of K. hexapunctata, K. neothunni, and K. konishiae n. sp. were clarified for the first time.
The naturalization of alien Reeves's muntjacs (Muntiacus reevesi) on Izu-Oshima Island, Tokyo, Japan, has proceeded intensively over the last five decades. To clarify whether the gastrointestinal helminths of these animals were brought from their original endemic area or were newly acquired in Japan, 32 Reeves's muntjacs trapped on the island were parasitologically examined. In addition to Gongylonema pulchrum in the oesophagus (34.4% prevalence), Chabaudstrongylus ninhae (Dróżdż, 1967) (Trichostrongylidae: Cooperiinae) and Oesophagostomum muntiacum Jian, 1989 (Chabertiidae: Oesophagostominae) were prevalent in the small (28.1%) and large (46.9%) intestines, respectively. For the first time, these trichostrongylid or chabertiid worms were genetically characterized based on partial nucleotide sequences of the nuclear ribosomal RNA gene (rDNA) and mitochondrial DNA cytochrome c oxidase subunit 1 gene (cox-1), and the phylogenetic relationships with other members of their family were explored. Since these two intestinal nematode species are inherent in muntjacs, this study demonstrates a new distribution of exotic helminth species in Japan in accordance with the naturalization of alien mammalian hosts. The molecular genetic data collected here could assist the taxonomic assessment of morphological variants in different Muntiacus spp. and/or of different geographical origins. Furthermore, our data may help to define the phylogenetic relationships among such isolates.
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