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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..


Kamiyama T.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Journal of Experimental Marine Biology and Ecology | Year: 2013

The value of planktonic ciliates as prey for the asexual reproduction of the polyp stage of the moon jellyfish (Aurelia aurita) was investigated by monitoring somatic growth (calyx diameter), bud production and prey consumption of polyps on a diet of the tintinnid ciliate Favella taraikaensis labeled with a stable nitrogen isotope (15N). These results were compared with those for polyps on a diet of metazoan larvae (Artemia spp.). In addition, nitrogen and carbon specific gross growth efficiencies on the ciliate diet were estimated from increased 15N content of polyps and consumption of ciliate 15N, and from the increase of polyp dry-weight (somatic growth and bud production), a weight:carbon factor and consumption of ciliate carbon, respectively. The calyx diameter of polyps increased with incubation time during the first 7-10days with ciliate prey and during the first 11-15days with Artemia prey. Bud production started after a lag period of 6-7days in all prey treatments, and the cumulative bud number increased with incubation time. The mean bud production rates after the initial lag period were higher with larger amounts of prey and estimated at 0.08-0.38indpolyp-1d-1 with ciliate prey and 0.12-0.35ind.polyp-1d-1 with Artemia prey. The mean relative change in calyx diameter with Artemia prey between day 10 and day 15 was significantly higher than that with ciliates at the same prey carbon supply, but bud production rate on a diet of Artemia consumed at 5μg-Cpolyp-1d-1 was significantly lower than that on a diet of ciliates consumed at the same rate. Promotion of bud production of polyps on a diet of ciliates rather than the somatic growth may be related to fragility characteristic of the ciliate prey, which are easily digested and absorbed. The nitrogen specific gross growth efficiency of A. aurita polyps on a diet of ciliates ranged from 59% to 78% (mean 68%). The relatively high values were supported by high carbon specific gross growth efficiencies ranging from 42% to 64% (mean 54%). This characteristic of polyp may be due to the small size and the low metabolic loss of assimilated energy source. These results indicate that planktonic ciliates, which are readily available to polyps in nature, can serve as a sufficient diet for asexual production of A. aurita polyps. © 2013 Elsevier B.V.


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.


Kamiyama T.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Journal of Experimental Marine Biology and Ecology | Year: 2011

To clarify the value of planktonic ciliates as a prey source for the moon jellyfish (Aurelia aurita), feeding rates of the polyp stage on Favella ehrenbergii, Strombidium sp., and Myrionecta rubra were quantified in laboratory experiments. The feeding responses on ciliates were compared with those on phytoplankton with similar equivalent spherical diameters (ESDs) by observation of the feeding behavior. The assimilation of ciliates ingested by A. aurita was examined by providing the ciliate Strombidinopsis jeokjo, labeled with nitrogen stable isotope (15N), to the polyps. A. aurita polyps fed on all species of ciliates. Feeding rates of A. aurita polyps as a function of ciliate concentration were fitted to a rectangular hyperbolic equation, and the maximum feeding rate was ca. 32cellsind-1h-1 (0.33μgCind-1h-1) for all ciliate species. The maximum feeding rate on M. rubra was significantly lower than those on the other ciliate genera, which is probably caused by the smaller cell size and distinctive motility of this species. Feeding incidences, defined by the movement of polyp tentacles, rarely occurred on nanophytoplankton with ESDs of ca. 20μm, and the feeding incidence on microphytoplankton with ESDs of ca. 30μm was significantly lower than that on a ciliate with a similar ESD, implying that phytoplankton is not an essential prey for mature A. aurita polyps. After polyps fed on 15N-labeled ciliates, the average nitrogen stable isotope ratio of polyps in the experimental treatments was significantly higher than that in the control, indicating that the polyps were able to assimilate nutrients from the captured ciliates. These results indicate that planktonic ciliates, a main component of microzooplankton and a frequently encountered energy source, likely serve as available food items for A. aurita polyps. © 2011 Elsevier B.V.


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.


Kurita J.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Nakajima K.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Viruses | Year: 2012

The genus Megalocytivirus, represented by red sea bream iridovirus (RSIV), the first identified and one of the best characterized megalocytiviruses, Infectious spleen and kidney necrosis virus (ISKNV), the type species of the genus, and numerous other isolates, is the newest genus within the family Iridoviridae. Viruses within this genus are causative agents of severe disease accompanied by high mortality in multiple species of marine and freshwater fish. To date outbreaks of megalocytivirus-induced disease have occurred primarily in south-east Asia and Japan, but infections have been detected in Australia and North America following the importation of infected ornamental fish. The first outbreak of megalocytiviral disease was recorded in cultured red sea bream (Pagrus major) in Japan in 1990 and was designated red sea bream iridovirus disease (RSIVD). Following infection fish became lethargic and exhibited severe anemia, petechiae of the gills, and enlargement of the spleen. Although RSIV was identified as an iridovirus, sequence analyses of RSIV genes revealed that the virus did not belong to any of the four known genera within the family Iridoviridae. Thus a new, fifth genus was established and designated Megalocytivirus to reflect the characteristic presence of enlarged basophilic cells within infected organs. Indirect immunofluorescence tests employing recently generated monoclonal antibodies and PCR assays are currently used in the rapid diagnosis of RSIVD. For disease control, a formalin-killed vaccine was developed and is now commercially available in Japan for several fish species. Following the identification of RSIV, markedly similar viruses such as infectious spleen and kidney necrosis virus (ISKNV), dwarf gourami iridovirus (DGIV), turbot reddish body iridovirus (TRBIV), Taiwan grouper iridovirus (TGIV), and rock bream iridovirus (RBIV) were isolated in East and Southeast Asia. Phylogenetic analyses of the major capsid protein (MCP) and ATPase genes indicated that although these viruses shared considerable sequence identity, they could be divided into three tentative species, represented by RSIV, ISKNV and TRBIV, respectively. Whole genome analyses have been reported for several of these viruses. Sequence analysis detected a characteristic difference in the genetic composition of megalocytiviruses and other members of the family in reference to the large and small subunits of ribonucleotide reductase (RR-1, RR-2). Megalocytiviruses contain only the RR-2 gene, which is of eukaryotic origin; whereas the other genera encode both the RR-1 and RR-2 genes which are thought to originate from Rickettsia-like α-proteobacteria. © 2012 by the authors; licensee MDPI, Basel, Switzerland.


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.


Murashita K.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kurokawa T.,Tohoku National Fisheries Research Institute
General and Comparative Endocrinology | Year: 2011

The neuropeptide cocaine- and amphetamine-regulated transcript (CART) is important in the regulation of food intake in mammals and fish. The tissue distributions of six CART cDNAs (cart ch3, ch4, ch6, ch9, ch11, and ch22) from medaka, Oryzias latipes, were cloned and the effect of starvation on their expression was examined. As in other species, medaka cart ch3, ch4, ch6, ch9, and ch22 consisted of three exons, while medaka cart ch11 contained four. The six cysteine residues at the C-terminal end of the CART motif and three-dimensional structure were well conserved in all medaka CART peptides. Tissue distribution analysis revealed that cart ch3, ch4, ch6, ch11, and ch22 were primarily expressed in the brain, but that the highest rates of cart ch9 expression occurred in the skin, suggesting different functions among the homologous genes. Although CART ch3 mRNA levels decreased in response to 17. days starvation, these levels were restored by re-feeding. However, the finding that the five other CART mRNAs did not respond to starvation suggests that only CART ch3 has an anorexigenic function in medaka. © 2010 Elsevier Inc.


Tanaka H.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Fisheries Science | Year: 2014

Eel aquaculture, though thriving nowadays, is totally dependent on the successful capture of wild eel fry and glass eels for its seedlings. The declination of eel resources in recent years has resulted in an urgent need for technology development in artificial seedlings production on an aquaculture basis, in order to protect natural resources and to stabilize the eel supply in the farming industry. Since the life history of the eel holds many mysteries, artificial hatching and rearing of larvae has long been regarded as an extremely difficult task. However, in recent years, the spawning ground of the Japanese eel has finally been located after continuous effort with intensive marine surveys, in which wild parental eels were captured, followed by the collection of fertilized eggs and the harvest of newly hatched preleptocephali. Meanwhile, through the collaborative efforts of many researchers, progress has also been made in improving technologies for artificial maturation of parental eels, which do not mature naturally in captivity, as well as in the technology for artificial hatching. Moreover, a technology for producing feed-rearing eel hatchlings, the most challenging process of all, has advanced rapidly after suitable feed was developed in the 1990s. Then, in 2002, for the first time in the world, larvae were successfully reared up to the glass eel stage, and second generation artificial hatchlings were born in 2010. In this way, eel farming technology that is not reliant on natural resources has been developed. There are strong hopes now for a technology for stable mass production of glass eels to be developed in the near future. © 2014, The Author(s).


Miyamoto K.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Hydrobiologia | Year: 2016

We investigated the effects of body color luminance and behavioral characteristics of stocked juvenile white-spotted charr, masu salmon, rainbow trout, albino rainbow trout, and non-spotted rainbow trout on their predation risk by predatory land animals. Body color luminance and behavioral characteristics were scored before starting the predation test. The dorsal color luminance of the albino rainbow trout was brighter than that of the other fish. The white-spotted charr and non-spotted rainbow trout were less active than the masu salmon and rainbow trout, and the non-spotted rainbow trout stayed in the open more than the white-spotted charr during behavioral observations in an aquarium. A piscivorous bird, the grey heron was the most frequently observed land animal during the predation test conducted at a semi-natural stream study site. The survival rate of total fish groups was 21.4 %, only 3 % albino rainbow trout and 11 % non-spotted rainbow trout survived, which were significantly lower than the survival rate of the other fish. These results suggest that the body color luminance of albino rainbow trout and the behavioral characteristics of non-spotted rainbow trout were important vulnerability factors. © 2015, Springer International Publishing Switzerland.

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