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Saitoh K.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Suzuki N.,Natural History Museum and Institute | Ozaki M.,Chiba Prefectural Fisheries Research Center | Ishii K.,Ibaraki Prefectural Government | And 4 more authors.
Nature Conservation | Year: 2017

Overuse of natural resources by humans is a major threat to biodiversity. Overuse often involves species of economic or esthetic value, and fish are a typical example for a group that is exploited both for economic reasons (for human consumption) and for esthetic reasons (e.g. by aquarists). Pseudorhodeus tanago (Tanaka, 1909) (formerly known as Tanakia tanago) is a small colorful but legally protected (fishing, keeping and transfer are banned) bitterling fish distributed around Tokyo, Japan. Whereas it is critically endangered and more and more habitat loss has occurred, at least four stocks have been newly found during the last decade. To explore whether emergence of these newly found habitats is a consequence of incomplete survey, we genotyped mitochondrial cytochrome b sequence of P. tanago from 17 localities and an illegal home aquarium. Populations known by the past extensive survey (13 localities) showed geographically structured population genetic characteristics. Population-specific haplotypes were common indicating past divergence and bottleneck events. Four (north, {center + west}, south-1, south-2) or five (north, center, west, south-1, south-2) geographic groups were detectable as for these known localities. On the other hand, newly found stocks were polymorphic and showed identical haplotypes from distant known localities. If we assume historical basis of distribution and genetic characteristics of these newly found stocks, it must be a series of unlikely geological events and haplotype sorting. We discuss potential issues posed by these questionable stocks.


Fukui Y.,Japan National Research Institute of Fisheries Science | Abe M.,National Fisheries University | Kobayashi M.,Seikai National Fisheries Research Institute | Shimada Y.,Chiba Prefectural Fisheries Research Center | And 4 more authors.
International Journal of Systematic and Evolutionary Microbiology | Year: 2014

Gram-stain-negative, aerobic, halophilic bacteria, designated SCM-1T, LCM10-1 and CTBL-B-147, were isolated from modified half-strength SWM-III medium, PES medium and thalli after laboratory cultivation of a red alga, Porphyra yezoensis. Phylogenetic analysis of 16S rRNA gene sequences indicated that the new isolates were affiliated to the genus Sulfitobacter of the class Alphaproteobacteria, and the 16S rRNA gene sequence similarity of the new isolates with the closest related species, Sulfitobacter mediterraneus CH-B427T, was 98.8 %. The DNA G+C contents of the new isolates were in the range of 61.4-62.3 mol%. DNA-DNA relatedness values of strain SCM-1T with other type strains of the genus Sulfitobacter were less than 15.9 %. The new isolates contained Q-10 as the predominant ubiquinone, phosphatidylcholine, phosphatidylglycerol, an unidentified amino lipid and an unidentified lipid as the main polar lipids, and C18: 1ω7c, C19: 1ω7c and C16: 0 as the major fatty acids (>10 % of the total). Strain SCM-1T could be differentiated from Sulfitobacter mediterraneus JCM 21792T by 35 morphological and phenotypic characteristics. On the basis of the phylogenetic, genetic and phenotypic properties of the new isolates, the name Sulfitobacter porphyrae sp. nov. is proposed, with strain SCM-1T (= LMG 27110T = NBRC 109054T) as the type strain. © 2014 IUMS.


Tanaka N.,Tsukuba Botanical Garden | Demise T.,Chiba University | Ishii M.,Chiba Prefectural Fisheries Research Center | Shoji Y.,Chiba Prefectural Fisheries Research Center | Nakaoka M.,Hokkaido University
Marine Biology | Year: 2011

Massive losses of eelgrass Zostera marina beds in Japan have occurred over the past 100 years. Toward their restoration, transplantation of eelgrass has been attempted in some areas, including Tokyo Bay. This study examined population genetic structures and gene flow in eelgrass in Tokyo Bay to establish guidelines for conducting restoration. Genotypes of a total of 360 individuals from 12 beds were determined using five microsatellite markers. The eelgrass beds in inner bay had above-average genetic diversity. A neighbor-joining tree based on FST values among beds revealed that a strong gene flow had occurred among six beds in the inner bay. Genetic assignment testing of drifting shoots indicated that those with seeds migrate in both directions between the inner and outer bay. We suggested that the restoration of eelgrass in the innermost part of Tokyo Bay, where natural habitats have been lost, should be conducted using the inner bay beds. © 2011 Springer-Verlag.


Kodama K.,Japan National Institute of Environmental Studies | Tajima Y.,Kanagawa Prefectural Fisheries Technology Center | Shimizu T.,Kanagawa Prefectural Fisheries Technology Center | Ohata S.,Chiba Prefectural Fisheries Research Center | And 2 more authors.
Marine Pollution Bulletin | Year: 2014

We investigated effects of severe hypoxia (dissolved oxygen <1 mll-1) on recruitment of mantis shrimp Oratosquilla oratoria in Tokyo Bay. Ten-year field surveys were conducted to examine quantitative relationships in annual mean densities of larvae and juveniles, and spatial distribution of juveniles and severe hypoxia. There was no significant correlation between annual mean densities of larvae and juveniles, suggesting that mortality during larval or juvenile stages varies among years, which might have regulated abundance of young-of-the-year juveniles. Juvenile density was low in the severely hypoxic area, implying that hypoxia could affect survivals and spatial distribution of juveniles. Meanwhile, there are yearly fluctuations in juvenile density in normoxic areas of both northern and southern part of the bay. This evidence suggests that abundance of post-settled juveniles might have been determined by not only effects of hypoxia, but also other factors influencing mortality during the early life stages. © 2014 Elsevier Ltd.


Kitade Y.,Tokyo University of Marine Science and Technology | Igeta Y.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Fujii R.,Canon Inc. | Ishii M.,Chiba Prefectural Fisheries Research Center
Journal of Oceanography | Year: 2011

Monitoring using a thermistor array and an acoustic Doppler current profiler was carried out in the outer part of Tokyo Bay from May 20 to November 30, 2006. Current fluctuations with tidal periods were amplified during the maximum temperature period in early September. The strong current interfered with fishing operations using set nets. Although the current fluctuation was speculated to be baroclinic motion from a phase relationship among fluctuations of temperature, current and sea level, empirical orthogonal function analysis showed the dominance of a barotropic structure. Such a discrepancy in the current structure was explained by an internal tide propagating along a deep canyon in the outer part of Tokyo Bay. Furthermore, amplification of the semidiurnal internal tide and the warming of the temperature field were found to be induced by the intrusion of Kuroshio warm water. The amplification mechanism was examined using a two-dimensional model with idealized topography. It was concluded that the large amplitude of the semidiurnal internal tide is resonantly generated in the deep canyon in the outer Tokyo Bay when stratification becomes strong and the period of the internal seiche approaches the semidiurnal period. © 2011 The Oceanographic Society of Japan and Springer.


Isojima T.,Kyoto University | Makino N.,Chiba Prefectural Fisheries Research Center | Takakusagi M.,Chiba Prefectural Fisheries Research Center | Tagawa M.,Kyoto University
Fisheries Science | Year: 2013

Abnormal flounder coloration frequently occurs in flounder hatcheries and diminishes the commercial value of the fish. To understand hypermelanosis, the progression of staining-type hypermelanosis in normally metamorphosed juveniles and ocular-side pigmentation in pseudoalbino juveniles were examined in the Japanese flounder Paralichthys olivaceus. Sixty-five days post hatching, juveniles (total length, 6 cm) were individually identified by color-marker implantation, and the darkened area of the body surface was examined for 10 weeks by image analysis of digital photographs of the fish taken from above or below the transparent tank. Staining was observed to mainly begin at the upper and lower bases of the tail fin, expanded anteriorly along the peripheral part of the trunk, and ceased after 2 months. The individuals in which staining occurred earlier expressed severe staining and small body size by the end of the experiment. Further, pigmentation of the ocular side in pseudoalbino juveniles ceased after 2 months, but the order of pigmentation was different from that on the blind side. In this case, darkening began from the posterior, but expanded from the center to the periphery of the trunk. Even at the end of the experiment, ctenoid scales were exclusively found within the darkened area, together with cycloid scales. © 2013 The Japanese Society of Fisheries Science.


Ohata S.,Chiba Prefectural Fisheries Research Center | Ishii M.,Chiba Prefectural Fisheries Research Center | Kajiyama M.,Chiba Prefectural Fisheries Research Center
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2013

To examine the settlement period of juvenile Fulvia mutica and their growth, monthly dredge sampling was conducted at 24 sampling sites in Tokyo Bay from 2006 to 2010. According to shell length frequency analysis, the sampling sites were divided into two areas: northern and southern sea areas. In the northern sea area, many of the juveniles that had settled in autumn appeared from early winter, and disappeared the next summer probably due to the hypoxic water. On the other hand, in the southern sea area, while many of the juveniles that had settled in spring were caught even in summer, their growth was not observed until early autumn. A possible cause of the growth stagnation is hypoxic water, which develops during the summer. The growth of juveniles started in early winter in both sea areas, and the time taken to grow from 20 mm to 60 mm in shell length was shorter in the northern sea area than in the southern sea area.


Toba M.,Chiba Prefectural Fisheries Research Center | Ito M.,Tokyo University of Marine Science and Technology | Kobayashi Y.,Chiba Prefectural Fisheries Research Center
Journal of Shellfish Research | Year: 2011

There have been numerous attempts to create and/or develop harvestable tidal areas where juveniles of the natural Manila clam Ruditapes philippinarum may be abundantly stocked. To prevent erosion and/or promote the colonization of natural juveniles through improving the physical stability of bottom sediment, it is important to understand the mechanisms that regulate dispersal and recolonization of benthic juveniles. The physical transport of bottom sediment is known to have a substantial effect on the spatial distribution patterns of infaunal bivalves in intertidal soft-bottom habitats. During the summers of 2004 and 2005, we conducted field experiments to identify the physical transport mechanisms for newly-settled postlarval Manila clams until growth to a size of 1 mm shell length at the Banzu tidal flat of Tokyo Bay in Japan. We used sediment traps to collect natural and released hatchery-reared juveniles, in parallel to acquiring measurements of seawater flow and observations of the spatial distribution of newly-settled natural juveniles. There was a sharp increase in the number of clams that were collected in the traps placed on the soft-bottom surface when τ w (wave shear stress) exceeded 0.3 N m -2. Because the τ c (advection shear stress) was far lower than τ w (τ c/τ w =1/601/130), the initiation of juvenile transport appeared to depend primarily on wave-generated oscillatory flow. The number of trapped juveniles regressed linearly to the weight of the sediment that was simultaneously collected in the trap (R 2 = 0.99, 0.81), which indicated that clams were transported in a similar way to that of sediment grains, despite juveniles and sand particles exhibiting different physical properties (size and specific gravity). Hence bedload transport may have resulted from the biologically induced adhesion of juvenile clams to sediment grains and/or their burrowing behavior. In the release-recovery experiment of marked juveniles, a larger number of clams were recovered from traps that had been placed downstream of the water current from the release point. A denser distribution of the natural Manila clam population settled in mid-July 2004, and subsequently moved several hundreds of meters inshore within a one month period. The concurrent monitoring of bottom flow during a total 4 wk period in the summer of 2004 indicated that τ w frequently exceeded the incipient threshold of bedload transport (assumed to be 0.3 N m -2). Consequently, the bedload movement of Manila clam juveniles in the study area was expected to be initiated at a wave shear stress that was greater than the incipient threshold, and in a downstream direction of the advection current. Because juvenile clams in the summer population appeared to be frequently subjected to hydrodynamic stress, which forces juveniles to move and halt incidentally in the early benthic stages, physical transport is likely to contribute to the changing pattern of juvenile distribution at the Banzu tidal flat of Tokyo Bay in Japan.


Gomi Y.,Mie University | Gomi Y.,Chiba Prefectural Fisheries Research Center | Miyazaki T.,Mie University
Fisheries Science | Year: 2015

In teleosts, the area of peak ganglion cell density in the retina (area centralis, AC) is thought to reflect the primary visual axis for feeding. The bluegill Lepomis macrochirus are known to undergo ontogenetic shifts in diet preference, but because their diet is affected by population density, interspecific competition, and seasonal changes in prey availability, they are considered generalist predators. We investigated whether the diet shifts of the bluegill were associated with a change in the location of the AC (total length of fish specimens, range 44–243 mm). The AC was located temporally in the retina of smaller fish (40–100 mm), and the area of increased density included the ventral and central regions of the retina. Conversely, the AC was located in the dorso-temporal region of the retina in larger (100–200 mm) fish. Lastly, in the largest bluegill (> 200 mm), the AC was located in the temporal region of the retina. In all cases, the orientation of the visual axis was consistent with the known diet preferences of the different size classes. © 2015, Japanese Society of Fisheries Science.


Isojima T.,Kyoto University | Makino N.,Chiba Prefectural Fisheries Research Center | Miyama Y.,Chiba Prefectural Fisheries Research Center | Tagawa M.,Kyoto University
Fisheries Science | Year: 2014

We previously reported that the progression of staining-type hypermelanosis spontaneously ceased at a specific time and area in Japanese flounder Paralichthys olivaceus. To examine whether time is a limiting factor in the spontaneous cessation of staining, we experimentally controlled the initiation and duration of staining by manipulating the bottom substrate condition in the fish tanks. At 151 days post hatching (DPH; 11 weeks), spontaneous cessation of staining was observed in fish reared in tanks without a sandy substrate. However, staining resumed (or was initiated) in tanks where sand was removed from 11 weeks, indicating a strong but temporary effect of bottom sand and the absence of time limitation in the staining progression by 151 DPH. Extended duration of the inhibitory period of hypermelanosis expansion (9 weeks or more) aided in only a 20 % reduction of the final staining area because of the increased rate of staining expansion. The bottom sandy substrate decreased the visibility of the staining area in individuals, but this was observed only before the completion of the staining expansion. These findings are discussed in relation to possible presence of area limitation of future staining, as well as the fundamental nature of staining. © 2014 The Japanese Society of Fisheries Science.

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