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Yamaguchi T.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kitano T.,Kumamoto University
Biochemical and Biophysical Research Communications | Year: 2012

The Japanese flounder (Paralichthys olivaceus) is a teleost fish with an XX/XY sex determination system. XX flounder can be induced to develop into phenotypic females or males, by rearing them at 18. °C or 27. °C, respectively, during the sex differentiation period. Therefore, the flounder provides an excellent model to study the molecular mechanisms underlying temperature-dependent sex determination. We previously showed that cortisol, the major glucocorticoid produced by the interrenal cells in teleosts, causes female-to-male sex reversal by directly suppressing mRNA expression of ovary-type aromatase (cyp19a1), a steroidogenic enzyme responsible for the conversion of androgens to estrogens in the gonads. Furthermore, an inhibitor of cortisol synthesis prevented masculinization of XX flounder at 27. °C, suggesting that masculinization by high temperature is due to the suppression of . cyp19a1 mRNA expression by elevated cortisol levels during gonadal sex differentiation in the flounder. In the present study, we found that exposure to high temperature during gonadal sex differentiation upregulates the mRNA expression of retinoid-degrading enzyme (cyp26b1) concomitantly with masculinization of XX gonads and delays meiotic initiation of germ cells. We also found that cortisol induces . cyp26b1 mRNA expression and suppresses specific meiotic marker . synaptonemal complex protein 3 (sycp3) mRNA expression in gonads during the sexual differentiation. In conclusion, these results suggest that exposure to high temperature induces . cyp26b1 mRNA expression and delays meiotic initiation of germ cells by elevating cortisol levels during gonadal sex differentiation in Japanese flounder. © 2012 Elsevier Inc.. Source


Satoh K.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Marine Ecology Progress Series | Year: 2010

Nine high density larval populations (patches) of Pacific bluefin tuna Thunnus orientalis were detected and 7 patches were tracked with reference buoys for 28 to 171 h in the northwestern Pacific Ocean in May-June 2004 to 2008. Buoy trajectories and surface current velocities and directions measured by acoustic Doppler current profiler data showed close agreement. Growth rates for the sampled larvae (3.0 to 9.9 mm standard length [SL], 4 to 17 d after hatch), estimated by the daily modes of SL, correspond to growth rates estimated from otolith daily ring analysis. These results indicate that the same populations were sampled by tracking the buoy on almost all the sampling days. At fine- (100s of m to km) and mid-scale observations (∼15 to 30 km range), patches consisted of a number of cohorts which had different distributions within the patch. The larval spatial structure was studied using variograms. At the fine scale, age-specific sills, ranges and spatial dependence of patches were similar; at the mid scale, these indexes showed stability during the trackings. Horizontally, larvae formed patches within an approximate 10 km range and advected together during the larval stage. Larvae were only distributed in the mixed layer and diel vertical movement was not clearly observed. Patches were entrained in mesoscale eddies (∼100 to 500 km diameter) which propagated westward. Such mesoscale eddies are known to coalesce with the Kuroshio current. The spawning area and the recruitment fishing grounds are thereby linked by the Kuroshio. Results suggest that cohorts have a stable spatial structure after fertilization (i.e. during advection, while entrained in mesoscale eddies). Therefore, the positional relationship between spawning events and mesoscale eddies is concluded to be important for the recruitment process. © Inter-Research 2010. Source


Yokoyama H.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Aquaculture | Year: 2013

In order to examine the efficiency of co-culturing fish with the Japanese common sea cucumber Apostichopus japonicus, field cultivation experiments were conducted in Gokasho Bay, central Japan. I cultured A. japonicus juveniles below a fish cage and at a control station for 238days, monitored the wet weight, and analyzed its stable carbon and nitrogen isotopes (δ13C, δ15N) together with potential food sources, and found that (1) juveniles cultured below fish cages exhibited high survivorship (96%) and significantly higher specific growth rate (1.9%) than those at the control site (1.2%), and (2) the juveniles had significantly reduced δ13C values (mean±SD=-19.1±0.3% vs. -17.5±0.4% at the control station), suggesting the incorporation of C3 plant material in fish feed through fish feces and settling organic matter. All sea cucumbers which were further cultured for additional 307days below fish cages grew to the marketable size (range and mean wet weight=142-181g, 160g, n=9). In order to evaluate the effect of density on growth, 6 culture vessels, in which 1, 5, 10, 15, 20 and 25 juveniles of A. japonicus were stocked, were maintained below the fish cage over 118days. The results showed that the final mean weight of A. japonicus decreased from 6.68g to 0.94g as the density increased with a large variation of weight at the end of the experiment (coefficient of variation=52.1-62.2%), suggesting that there was competition between individuals for a limited food supply and there were intraspecific effects on the growth. This study shows the possibility of integrated multi-trophic aquaculture in which A. japonicus is cultured in the water column below fish cages, because the survival and growth of the sea cucumbers were enhanced due to the ability to avoid predator interactions and adverse environmental conditions as well as nutritional feed supply from the fish cage. © 2012 Elsevier B.V. Source


Kokita T.,Fukui Prefectural University | Nohara K.,Fukui Prefectural University | Nohara K.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Molecular Ecology | Year: 2011

Phylogeographical patterns of marine and diadromous organisms are often influenced by dynamic ocean histories. For example, the marine realm around the Japanese Archipelago is an interesting area for phylogeographical research because of the wide variation in the environments driven by repeated shifts in sea level in the Quaternary. We analysed mitochondrial cyt b gene and nuclear myh6 gene sequences for individuals collected from throughout the range of the anadromous fish Leucopsarion petersii to assess the lineage divergence, phylogeographical pattern and historical demography in relation to geological history and oceanographic features around the archipelago. Leucopsarion petersii has two major lineages (the Japan Sea and Pacific Ocean lineages), which diverged during the late-early to middle Pleistocene. Geographical distributions of the two lineages were closely related to the pathways of the two warm currents, the Tsushima Current and the Kuroshio Current, that flow past the archipelago. Evidence of introgressive hybridization between these lineages was found at two secondary contact zones. Demographic tests suggested that the Japan Sea and Pacific Ocean lineages carried the genetic signal of different historical demographic processes, and these signals are probably associated with differences in habitat stability during recent glacial periods. The Japan Sea lineage has a larger body-size and more vertebrae, probably in relation to severe habitat conditions through Pleistocene climatic oscillations. Thus, the two lineages have long independent evolutionary histories, and the phylogeographical structure and demography of this species have been influenced both by historical events and the present-day oceanography around the Japanese Archipelago. © 2010 Blackwell Publishing Ltd. Source


Imai I.,Hokkaido University | Yamaguchi M.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Harmful Algae | Year: 2012

The marine fish-killing raphidophytes of the genus Chattonella currently consist of five species, i.e. C. antiqua, C. marina, C. minima, C. ovata and C. subsalasa. The distribution of Chattonella species was confirmed in tropical, subtropical and temperate regions in the world accompanying mass mortalities of fishes in nature and in aquaculture. The fish-killing mechanisms are still unclear, but suffocation is the ultimate cause of fish death. Increasing evidence is pointing towards the generation of reactive oxygen species (ROS, e.g. superoxide), which are responsible for the gill tissue injury and mucus production that leads to death of fishes. A taxonomic revision was proposed based on morphology and genetic diversity that Chattonella antiqua and Chattonella ovata should be varieties of Chattonella marina possessing nomenclatural priority. Optimum temperatures for growth are 25°C for C. antiqua and C. marina, 25-30°C for C. ovata and 20-30°C for Chattonella subsalsa. Adequate ranges of salinity for growth were about 20-30 for Chattonella species. Chattonella cells generally divide once a day. Laboratory culture experiments with artificial synthetic medium demonstrated that C. antiqua, C. marina and C. ovata used only Fe chelated with EDTA for growth, although tested diatoms and dinoflagellates used rather many kinds of chelated Fe. A suitable concentration of humic acid supplied with iron also had enhancing effects on the growth of C. antiqua. Diel vertical migration was observed in Chattonella, and the cells reached 7.5. m deep at night in the case of C. antiqua demonstrated by a mesocosm experiment in the Seto Inland Sea. Chattonella species have diplontic life history and have haploid cyst stage in their life cycle. Encystment was observed through formation of pre-encystment small cells after the depletion of nitrogen, and the small cells sink to the sea bottom to complete cyst formation by attachment to the solid surface such as diatom frustules and sand grains. Newly formed cysts are in the state of spontaneous dormancy and they need cold temperature period of four months or longer for maturation (acquisition of germination ability). Cysts germinate in early summer and resultant vegetative cells play an important role as seed populations in blooming in the summer season. However, relatively small part of cyst populations actually germinate from bottom sediments, and success of red tide formation is dependent on the growth in water columns. Since red tides of Chattonella were observed when diatoms were scarce in seawater, diatoms appear to have a key for the predominance of Chattonella in water columns. Diatom resting stages in sediments need light for germination/rejuvenation, whereas Chattonella cysts can germinate even in the dark, implying the selective germination of Chattonella cysts at the sea bottom under calm oceanographic conditions which contribute to bloom formation of Chattonella. As a mechanism of red tide occurrences of Chattonella in coastal sea, " diatom resting hypothesis" was presented. Biological control using diatoms is proposed through the germination/rejuvenation of resting stages suspending from bottom sediments to euphotic layer by sediment perturbation with submarine tractors or fishing trawling gears. Since diatoms have much higher growth rates, and newly joined diatom vegetative cells grow faster and prevent occurrence of Chattonella red tides as a result. As another prevention strategy for Chattonella red tides, algicidal bacteria inhabiting in seaweed beds and seagrass beds are presented. Co-culture of fish and seaweeds in aquaculture areas, and the developments of seaweed- and seagrass-beds would be practical and ultimately environment-friendly strategies for the prevention of harmful red tides of Chattonella by virtue of natural algicidal bacteria supplied from seaweeds and leaves of seagrass. © 2011 Elsevier B.V. Source

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