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Kubota H.,Tochigi Prefectural Fisheries Experimental Station | Watanabe K.,Kyoto University | Suguro N.,Kanagawa Prefectural Fisheries Technology Center | Tabe M.,Baika High School | And 2 more authors.
Conservation Genetics | Year: 2010

The Tokyo bitterling Tanakia tanago (Cyprinidae) was once found throughout the Kanto Plain, central Japan, but most of their habitats have been lost due to human activities such as urbanization and improvement of paddy fields. Subsequently, conservation efforts, including captive breeding and reintroduction, have been ongoing. However, the genetic relationships among populations of this species including captive and remnant wild populations have been uncertain and thus management units for this species have been unidentified. We examined the population differentiation among 12 populations, including four wild and eight captive populations, and their relative genetic diversities to assist in conservation management decisions. Phylogeographic analyses based on partial mitochondrial cytochrome b gene sequences and microsatellite polymorphisms revealed four geographically associated genetic groups in the populations. Northern Tochigi populations have diverged from other populations (0.77% of dA), likely stemming from allopatric fragmentation following a change in the route of the Naka River, which occurred during the middle of the Pleistocene epoch. Microsatellite analysis has revealed that the genetic diversity of each population is generally low, and that most of the populations have experienced genetic bottlenecks. For future in- and ex-situ conservation programs to succeed, the population structure and genetic variability of remnant populations need to be taken into consideration. © 2010 Springer Science+Business Media B.V.


Nakagawa H.,Kyoto University | Nakagawa H.,Hiroshima University | Seki S.,Kochi University | Ishikawa T.,Tochigi Prefectural Fisheries Experimental Station | Watanabe K.,Kyoto University
Ichthyological Research | Year: 2015

The genetic population structure of the Japanese amblycipitid catfish Liobagrus reinii was investigated using partial sequences of the mitochondrial DNA cytochrome b gene, focusing on the pattern associated with the Central Highlands (the Fossa Magna region), the major geographic barrier for Japanese freshwater fish. Phylogenetic analyses revealed two highly divergent lineages within this species (clades 1 and 2), with each lineage further divided into three or four allopatric subclades (1-1, 2, 3, 4 and 2-1, 2, 3), suggesting that geographic isolation, such as mountain uplifting, was the major factor influencing population structure. One exception was the co-occurrence of two subclades (1-1 and 2-1) in several rivers of the Chugoku and Shikoku regions of western Japan, which would have resulted from a secondary contact between historically isolated populations via river capture. Subclade 1-2 haplotypes were widely distributed in the central area of Honshu Island (Pacific side) across the Central Highlands, where population and species differentiations are often evident in freshwater fishes. This pattern, along with circumstantial evidence, supports the theory that eastern populations from the Pacific side of Honshu originated from artificial introduction. Together with the western limit of the northeastern populations on the Sea of Japan side of Honshu, the role of the Fossa Magna region as a geographic barrier was emphasized also in this species. Based on the deep intraspecific divergence of the species and large differentiation from continental congeners, L. reinii was concluded to be an old member of the Japanese freshwater fish fauna, which extended its distribution over the Japanese Archipelago at an early time. © 2015 The Ichthyological Society of Japan


Tsunagawa T.,Tochigi Prefectural Fisheries Experimental Station | Sakai T.,1 20 Hanawada | Yoshida Y.,Tochigi Prefectural Fisheries Experimental Station | Kubota H.,Tochigi Prefectural Fisheries Experimental Station | Sagawa S.,University of Hyogo
Ecology and Civil Engineering | Year: 2012

The microhabitat characteristics of the Tokyo bitterling, Tanakia tanago, designated a natural monument of Japan, were investigated in its natural habitat. To elucidate the habitat requirements of juvenile bitterling, we analyzed the relationships between the occurrence (presence/absence) of juveniles and microhabitat variables using a generalized linear mixed model (GLMM). The model showed that the occurrence of juveniles was positively correlated with the presence of underwater cover and the number of bitterling eggs deposited in adjacent mussels, and negatively correlated with current velocity. When the habitat was evaluated using this model, it predicted that the occurrence probability of juveniles was low in the upper reach of the canal. Therefore, the upper reach habitat was restored (i.e., the bottom was excavated, stakes were installed, and mussels were introduced) after considering the habitat requirements of juveniles. To assess the effect of these restorations, we compared the occurrence of juveniles between restored and control (non-restored) stations. Over the duration of the observations, 99 and 41 juveniles were found at restored and control stations, respectively; 71 % of the total number of juveniles was observed in the restored sections. These results suggest that the restoration scheme could increase suitable habitat for juvenile bitterling. Assuming that the juveniles observed in the upper reach of the canal survive and breed, the size of this population should increase. The habitat-requirement model constructed in this study should be applicable for maintenance and reconstruction of habitats of this species.


The maintenance of genetic diversity is one of the chief concerns in the captive breeding of endangered species. Using microsatellite and mtDNA markers, we examined the effects of two key variables (parental number and duration of breeding period) on effective population size (Ne) and genetic diversity of offspring in an experimental breeding program for the endangered Tokyo bitterling, Tanakia tanago. Average heterozygosity and number of alleles of offspring estimated from microsatellite data increased with parental number in a breeding aquarium, and exhibited higher values for a long breeding period treatment (9 weeks) compared with a short breeding period (3 weeks). Haplotype diversity in mtDNA of offspring decreased with the reduction in parental number, and this tendency was greater for the short breeding period treatment. Genetic estimates of Ne obtained with two single-sample estimation methods were consistently higher for the long breeding period treatment with the same number of parental fish. Average Ne/N ratios were ranged from 0.5 to 1.4, and were high especially in the long breeding period with small and medium parental number treatments. Our results suggest that the spawning intervals of females and alternative mating behaviors of males influence the effective size and genetic diversity of offspring in bitterling. To maintain the genetic diversity of captive T. tanago, we recommend that captive breeding programs should be conducted for a sufficiently long period with an optimal level of parental density, as well as using an adequate number of parents. © 2011 Wiley Periodicals, Inc.


Ishikawa T.,Tochigi Prefectural Fisheries Experimental Station | Ubukata H.,Nihon University | Mano N.,Nihon University | Hirose H.,Nihon University | Nakanishi T.,Nihon University
Fish Pathology | Year: 2012

Mortality associated with edema occurred in juvenile Japanese char Salvelinus leucomaenis. Scanning electron microscopy of gill surfaces and histological observations of the gills and kidneys of diseased juveniles indicated that the present pathological changes of the edema disease in juvenile Japanese char (EJJC) were similar to those of the previous study. We conducted three experiments to investigate curative and preventive measures for EJJC: a bath treatment with 1.0% salt water for a curative effect in the early stage of the disease, supplementation of ascorbic acid to the commercial diet (10,000 mg/kg diet) for prevention of the disease, and the supplementation of ascorbic acid along with increased water flow to improve the water quality also for the disease prevention. Results confirmed the curative effect of a 1.0% salt water bath treatment on the early stage of an EJJC outbreak, and the preventive effect on the dietary supplement of ascorbic acid with increasing water quantity before an outbreak. © 2012 The Japanese Society of Fish Pathology.


Tsuboi J.-I.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Takagi Y.,Tochigi Prefectural Fisheries Experimental Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2016

We investigated essential factors of the establishment of stocked ayu, Plecoglossus altivelis by going underwater with a snorkel to count the number of ayu individuals and measure the microhabitat in 25 rivers in Hokkaido, Honshu, and Kyushu. In our analysis, three factors were selected as explanatory variables for the number of ayu observed: 1) smaller river width, 2) higher frequency of boulders (over 25 cm in major axis) on the river bed, and 3) higher frequency of exposed boulders. These factors should be taken into account when making management decisions on stocking sites. The number of ayu individuals observed by snorkeling also positively correlated with catch per unit effort of "Tomozuri" angling in the Naka River. Therefore, the number of individuals counted by underwater observation may be an appropriate index of the abundance of ayu as a target for angling. © 2016 The Japanese Society of Fisheries Science.


Ishikawa T.,Tochigi Prefectural Fisheries Experimental Station | Mano N.,Nihon University | Nakanishi T.,Nihon University | Hirose H.,Nihon University
Fisheries Science | Year: 2011

The present study examined the effects of high-concentration ascorbic acid (AsA) supplementation over a long period on growth, plasma components, nonspecific immune responses, and thermal tolerance in rainbow trout Oncorhynchus mykiss. Four commercial diets supplemented with 0, 100, 1000, and 5000 mg AsA per kg of diet (designated AsA0, AsA100, AsA1000, and AsA5000, respectively) were fed to rainbow trout (initial weight 1.85 g) for 100 days. AsA contents in liver increased with increasing dietary AsA levels. Feeding period, growth performance, and plasma components did not differ significantly between the AsA groups. On the other hand, the phagocytic assay [nitro-blue tetrazolium (NBT) assay] was significantly higher in fish fed AsA1000 and AsA5000 than those fed a diet without AsA (AsA0) at the end of feeding trial. Superoxide dismutase (SOD) activity in the intestines of fish fed AsA5000 was also significantly higher than that of fish fed AsA0. In the thermal tolerance test, fish fed AsA5000 only showed significantly lower cumulative mortality compared with the AsA0 group. In conclusion, high-concentration AsA supplementation such as AsA5000 over a long period does not induce any adverse effects and can enhance disease and stress resistance in rainbow trout. © 2011 The Japanese Society of Fisheries Science.


Kubota H.,Tochigi Prefectural Fisheries Experimental Station | Sakai T.,Tochigi Prefectural Fisheries Experimental Station | Doi T.,Tochigi Prefectural Fisheries Experimental Station
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2010

Rotational fishing in mountain streams is a potential inland fisheries management practice for the sustainable exploitation of natural stocks. To evaluate the effects of rotational fishing on enhancement of white-spotted charr and masu salmon stocks, we investigated changes in the abundances of these fishes in two streams where this management practice was applied. Generalized linear mixed models showed that the density of catchable-size (> 150 mm) of both species increased during two closed years and three closed years in one stream. In another stream, the density of catchable-size charr did not increase during two closed years. The density of new recruits (≤ 150 mm) of either species did not increase in either stream, probably because of the effects of environmental fluctuations and time lags for population increase. Our data indicate that the effects of rotational fishing in mountain streams on enhancement of fish stocks differ among streams and fish sizes. Because the short-term closures investigated here resulted in only small increases in population (1-2 individuals/100 m 2), stocks may decline rapidly under high fishing pressure during open periods. Accordingly, additional harvest regulations may need to be implemented during open years to sustain the increased abundance resulting from rotational fishing.


Yoshimura M.,Japan Forestry and Forest Products Research Institute | Yokoduka T.,Tochigi Prefectural Fisheries Experimental Station
Science of the Total Environment | Year: 2014

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011 emitted radioactive substances into the environment, contaminating a wide array of organisms including fishes. We found higher concentrations of radioactive cesium (137Cs) in brown trout (Salmo trutta) than in rainbow trout (Oncorhynchus nerka), and 137Cs concentrations in brown trout were higher in a lake than in a stream. Our analyses indicated that these differences were primarily due to differences in diet, but that habitat also had an effect. Radiocesium concentrations (137Cs) in stream charr (Salvelinus leucomaenis) were higher in regions with more concentrated aerial activity and in older fish. These results were also attributed to dietary and habitat differences. Preserving uncontaminated areas by remediating soils and releasing uncontaminated fish would help restore this popular fishing area but would require a significant effort, followed by a waiting period to allow activity concentrations to fall below the threshold limits for consumption. © 2014 Elsevier B.V.


The maintenance of genetic diversity is one of the chief concerns in the captive breeding of endangered species. Using microsatellite and mtDNA markers, we examined the effects of two key variables (parental number and duration of breeding period) on effective population size (N(e) ) and genetic diversity of offspring in an experimental breeding program for the endangered Tokyo bitterling, Tanakia tanago. Average heterozygosity and number of alleles of offspring estimated from microsatellite data increased with parental number in a breeding aquarium, and exhibited higher values for a long breeding period treatment (9 weeks) compared with a short breeding period (3 weeks). Haplotype diversity in mtDNA of offspring decreased with the reduction in parental number, and this tendency was greater for the short breeding period treatment. Genetic estimates of N(e) obtained with two single-sample estimation methods were consistently higher for the long breeding period treatment with the same number of parental fish. Average N(e) /N ratios were ranged from 0.5 to 1.4, and were high especially in the long breeding period with small and medium parental number treatments. Our results suggest that the spawning intervals of females and alternative mating behaviors of males influence the effective size and genetic diversity of offspring in bitterling. To maintain the genetic diversity of captive T. tanago, we recommend that captive breeding programs should be conducted for a sufficiently long period with an optimal level of parental density, as well as using an adequate number of parents.

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