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Sato T.,Mie University | Sato T.,Kyoto University | Demise T.,Nara Women's University | Kubota H.,Tochigi Prefectural Fisheries Experiment Station | And 3 more authors.
Transactions of the American Fisheries Society | Year: 2010

The Kirikuchi char Salvelinus leucomaenis japonicus, which is endemic to the Kii Peninsula, central Honshu, Japan, is a relict nonanadromous char adapted to the southernmost habitats of the genus Salvelinus. As a result of anthropogenic disturbance, the distribution of the Kirikuchi char is now limited to the two upper drainages of the Totsu River system in the Kii Peninsula and this subspecies is now threatened with extinction. The present study determined the genetic population structure of the Kirikuchi char by using partial sequences of the mitochondrial cytochrome b gene, seven microsatellites, and a major histocompatibility complex (MHC) gene (exon 2 of MHC class II beta). The results indicated that native Kirikuchi char populations in both drainages have hybridized extensively with stocked S. leucomaenis pluvius or S. leucomaenis leucomaenis that were originally distributed in eastern Honshu. Native populations were restricted to isolated headwaters above natural falls or sediment control dams and showed very low genetic diversity: one mitochondrial DNA haplotype and average heterozygosity of 0.00-0.12 in microsatellites and 0.00-0.50 in the MHC gene. The distinct genetic differences between the Kirikuchi char populations in the two drainages suggest that these populations should be managed as separate conservation units. A high risk of hybridization with stocked nonnative subspecies widely distributed throughout the drainages has prevented the recovery of natural connections that permit gene flow between local populations of Kirikuchi char. Given the extremely low genetic diversity of the remaining Kirikuchi char populations, it is necessary to take proactive management measures, such as the promotion of artificial gene flow across local populations within each drainage and genetic restoration using the data presented here. © by the American Fisheries Society 2010.

Watanabe T.,Tochigi Prefectural Fisheries Experiment Station | Sawada M.,Tochigi Prefectural Fisheries Experiment Station | Yanagida T.,Asahikawa University | Yanagida T.,Yamaguchi University | Ogawa K.,Meguro Parasitological Museum
Fish Pathology | Year: 2014

We investigated the existence of Diphyllobothrium nihonkaiense plerocercoids and trematode metacercariae of the genus Metagonimus in salmonid fishes (N = 2,187) cultured in freshwater areas of Japan. The infection of D. nihonkaiense plerocercoid larvae was not detected in cultured freshwater salmonids, whilst five out of 60 wild anadromous masu salmon Oncorhynchus masou masou captured during the spawning migration in the Miomote River was infected with D. nihonkaiense. No Metagonimus metacercariae were detected in any salmonids examined. The present study corroborates the previous report indicating that salmonids cultured in freshwater areas of Japan have no chance of infection with D. nihonkaiense. © 2014 The Japanese Society of Fish Pathology.

Yoshida Y.,Tochigi Prefectural Fisheries Experiment Station | Ishizima H.,Tochigi Prefectural Fisheries Experiment Station | Mizuani M.,Utsunomiya University | Goto A.,Utsunomiya University
Ecology and Civil Engineering | Year: 2013

Fish spawning habitat preference was examined in an irrigation ditch of the Houki River in the Naka River system. Habitat types in the ditch were classified into five categories based on the physical characteristics of the environment. Eggs and larvae of Lefua echigonia and Cobitis sp. BIWAE type C, and eggs of Silurus asotus were collected in the ditch. Eggs of Lefua echigonia and Cobitis sp. BIWAE type C were observed in narrow, slow flowing, shallow areas out of the main current near the edge of the ditch in plant litter or vegetation. However, larvae of L. echigonia were found in wider and more vegetated areas in the main current than eggs. Eggs of S. asotus were found in wide, deep, slow moving areas in which litter and vegetation had been deposited. The findings of this study illustrated that the importance of microhabitat in spawning site selection, as well as the need to consider these factors when designing conservation measures for these species.

Yamamoto S.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Yokoduka T.,Tochigi Prefectural Fisheries Experiment Station | Fujimoto K.,Japan National Research Institute of Fisheries Science | Takagi K.,Japan National Research Institute of Fisheries Science | Ono T.,Japan National Research Institute of Fisheries Science
Journal of Fish Biology | Year: 2014

Approximately 18 months (September to December 2012) after the Fukushima Dai-ichi Nuclear Power Plant accident, elevated radiocaesium concentrations were measured in samples of muscle and eggs from masu salmon Oncorhynchus masou, kokanee Oncorhynchus nerka, brown trout Salmo trutta and lake trout Salvelinus namaycush from the Lake Chuzenji system, central Honshu Island, Japan (160km from the station). Mean muscle concentrations were 142·9-249·2Bqkg-1 wet mass and mean concentrations in eggs were 38·7-79·0Bqkg-1 wet mass. There was no relationship between fork length and muscle radiocaesium concentration in any of the species, but there were significant relationships between individual muscle and egg radiocaesium concentrations from O. masou, S. trutta and S. namaycush. Journal of Fish Biology © 2014 The Fisheries Society of the British Isles 84 5 May 2014 10.1111/jfb.12368 BRIEF COMMUNICATION BRIEF COMMUNICATIONS © 2014 The Fisheries Society of the British Isles.

Nakamura T.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Doi T.,Tochigi Prefectural Fisheries Experiment Station
Journal of Fish Biology | Year: 2014

The dominancy of semi-wild and hatchery-reared white-spotted charr Salvelinus leucomaenis juveniles was evaluated using pair-wise enclosure tests and field stocking tests. The semi-wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed-eggs. In the pair-wise enclosure test, the semi-wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (LS). The semi-wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were>11% larger in LS. In the field stocking test, the abundance and growth of semi-wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger LS). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi-wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be<10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi-wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed-egg stage is likely to increase their lowered aggression. © 2014 The Fisheries Society of the British Isles.

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