Kakehi S.,Tohoku National Fisheries Research Institute |
Ito S.-i.,Atmosphere and Ocean Research Institute |
Wagawa T.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Journal of Geophysical Research: Oceans | Year: 2017
We used salinity and potential alkalinity data from hydrographic observations to investigate surface mixing ratios in the Kuroshio-Oyashio mixed water region in the western North Pacific. In addition to mixing between the Kuroshio Extension (KE) and Oyashio, we assessed freshwater input/removal. A mixing scenario with three end-members was assumed in the surface layer ≤100 m. The results indicate that water masses near the sea surface in the Kuroshio-Oyashio mixed water region were mainly the result of mixing between the KE and Oyashio. The freshwater contribution was approximately 2.2% at depth 10 m. The volume of freshwater estimated from this percentage was consistent with surface water budgets estimated from reanalysis precipitation and evaporation data. The estimated mixing ratio of the KE (rk) along the quasi-stationary jet in the western North Pacific, which splits from the KE and flows northeastward toward the subarctic region, decreased downstream from 95% to 27% in only 42 days, suggesting that water properties were changed rapidly by mixing. Correlation between rk around the quasi-stationary jet and nutrients concentration was significantly negative in the layer where photosynthesis was negligible, indicating that the mixing between the KE and Oyashio is an important determinant of the horizontal distribution of nutrients in this area. © 2017. American Geophysical Union.
The effect of temperature on the duration of spawning markers-migratory-nucleus and hydrated oocytes and postovulatory follicles- in the multiple-batch spawner Japanese flounder (Paralichthys olivaceus)
Kurita Y.,Tohoku National Fisheries Research Institute |
Fujinami Y.,Fisheries Research Agency |
Amano M.,Kitasato University
Fishery Bulletin | Year: 2011
The duration of spawning markers (e.g. signs of previous or imminent spawnings) is essential information for estimating spawning frequency of fish. In this study, the effect of temperature on the duration of spawning markers (i.e., oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, as well as new postovulatory follicles) of an indeterminate multiple-batch spawner, Japanese f lounder (Paralichthys olivaceus), was evaluated. Cannulation was performed to remove samples of oocytes, eggs, and postovulatory follicles in individual females at 2-4 hour intervals over 27-48 hours. The duration of spawning markers was successfully evaluated in 14 trials ranging between 9.2° and 22.6°C for six females (total length 484-730 mm). The durations of spawning markers decreased exponentially with temperature and were seen to decrease by a factor of 0.16, 0.36, 0.30, and 0.31 as temperature increased by 10°C for oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, and new postovulatory follicles, respectively. Thus, temperature should be considered when estimating spawning frequency from these spawning markers, especially for those fish that do not spawn synchronously in the population.
Froiland E.,University of Tromsø |
Murashita K.,Tohoku National Fisheries Research Institute |
Jorgensen E.H.,University of Tromsø |
Kurokawa T.,Tohoku National Fisheries Research Institute
General and Comparative Endocrinology | Year: 2010
Anadromous (sea-migrating) Arctic charr (Salvelinus alpinus) display pronounced seasonal variations in food intake and growth and is an interesting model for studying mechanisms of appetite regulation. In this study cDNAs encoding for ghrelin (GHRL) and leptin (LEP) in Arctic charr were cloned, after which stomach GHRL and liver LEP mRNA expressions were examined by qPCR during a seasonal feeding cycle of semi-wild anadromous Arctic charr. The fish were captured as they returned from summer feeding in seawater and transferred to an indoor tank where they were fed in excess until October the year after. Growth rate was low in late winter, increased in late spring and reached a peak during summer, and then declined during autumn, when the fish became sexually mature. The changes in growth rate were associated with corresponding changes in the proportion of fish that had been eating at each sampling date, and whole body lipid status. Stomach GHRL mRNA expression was high in late winter, decreased to a nadir in mid-summer and increased again to a high level in early autumn. Liver LEP mRNA remained low during winter, spring and early summer, after which there was a gradual, 7-fold increase until October. The seasonal changes in ghrelin and leptin support a role of these hormones in the long-term regulation of energy homeostasis in the anadromous Arctic charr. It cannot be excluded, however, that the increase in liver leptin expression during autumn is related to sexual maturation. © 2009 Elsevier Inc. All rights reserved.
Saito H.,Japan National Research Institute of Fisheries Science |
Aono H.,Japan National Research Institute of Fisheries Science |
Aono H.,Tohoku National Fisheries Research Institute
Food Chemistry | Year: 2014
Phosphatidylethanolamine and phosphatidylcholine were major components in the foot lipids of the turban shell Turbo cornutus, while triacylglycerol was the major one in its viscera, which demonstrate the high level of lipid in all specimens. The major polyunsaturated fatty acids (PUFA) in the major lipid classes of T. cornutus were 20:4n-6 (arachidonic acid; ARA), 20:5n-3 (ecosapentaenoic acid; EPA), 22:4n-6, and 22:5n-3 (docosapentaenoic acid; n-3 DPA), with very low levels of 22:6n-3 (docosahexaenoic acid; DHA). The unusual high levels of ARA, 22:4n-6, and n-3 DPA found in both the triacylglycerols and phospholipids of all specimens suggest the influence of dietary algae on its tissue lipids. In the polar lipids, the total PUFA content was consistently high, with n-6 PUFA compensating for the fluctuation in the total n-3 PUFA levels. T. cornutus concentrated high levels of ARA in the visceral lipids from the dietary algae whose lipid content were very low. The viscera may effectively serve as a source of ARA for infant formulas. High levels of ARA, EPA, and n-3 DPA in the phospholipids of T. cornutus were observed. T. cornutus is a healthful marine food containing high levels of n-3 DPA. © 2013 Elsevier Ltd. All rights reserved.
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.
Sakami T.,Tohoku National Fisheries Research Institute
Microbes and Environments | Year: 2011
Ammonia oxidization is the first and a rate-limiting step of nitrification, which is often a critical process in nitrogen removal from estuarine and coastal environments. To clarify the correlation of environmental conditions with the distribution of ammonia oxidizers in organic matter-rich coastal sediments, ammonia-oxidizing archaea (AOA) and bacteria (AOB) ammonia monooxygenase alpha subunit gene (amoA) abundance was determined in sediments of Matsushima Bay located in northeast Japan. The AOA and AOB amoA copy numbers ranged from 1.1×10 6 to 1.7×10 7 and from 7.1×10 5 to 7.6×10 6 copies g -1 sediment, respectively. AOA and AOB amoA abundance was negatively correlated with dissolved oxygen levels in the bottom water. AOA amoA abundance was also correlated with total phosphorus levels in the sediments. On the other hand, no significant relationship was observed between the amoA abundance and ammonium, organic matter (ignition loss), or acid volatile sulfide-sulfur levels in the sediments. These results show the heterogeneous distribution of ammonia oxidizers by the difference in environmental conditions within the bay. Moreover, AOA amoA diversity was relatively low in the area of high AOA amoA abundance, suggesting the variability of AOA community composition.
Tamate T.,Tohoku National Fisheries Research Institute
Zoological Science | Year: 2015
Evolutionary ecologists often expect that natural and sexual selection result in systematic co-occurrence patterns of sex-biased mortality and sexual size dimorphism (SSD) within animal species. However, whether such patterns actually occur in wild animals is poorly examined. The following expectation, the larger sex suffers higher mortality, was primarily tested here for apparently native sea-run masu salmon (Oncorhynchus masou) in three populations in Hokkaido, Japan. Field surveys on sex ratios, body sizes, and ages of smolts and returning adults revealed that two of the three populations exhibited an expected pattern, a female-biased marine mortality and SSD, but one population demonstrated an unexpected co-occurrence of male-biased marine mortality and female-biased SSD. These female-biased SSDs were attributed to faster marine growth of females because of no sex difference in smolt body size. It has been previously suggested that breeding selection favoring large size generally act more strongly in females than in males in Japanese anadromous masu, as there is a weak sexual selection on adult males but universally intensive natural selection on adult females. Thus, this hypothesis explains female-biased SSDs well in all study populations. Interpopulation variation in sex-biased mortality found here might result from differences in marine predation and/or fishing pressures, given that selection driving female-biased SSD makes females forage more aggressively than males during the marine phase. Taken together, these results raise the possibility that evolutionary forces have shaped adaptive sex-specific foraging strategies under relationships between growth and mortality, resulting in co-occurrence patterns of sex-biased mortality and SSD within animal species. © 2015 Zoological Society of Japan.
Takahashi K.,Tohoku National Fisheries Research Institute |
Ide K.,Tohoku National Fisheries Research Institute
Hydrobiologia | Year: 2011
The response of large calanoid, Eucalanus bungii, to environmental fluctuation, particularly in relation to the spring diatom bloom in the Oyashio region, western subarctic Pacific Ocean, was examined by investigating egg production, grazing, development and starvation tolerance. Mean in situ egg production rate increased with ambient chlorophyll-a concentration, ranging from 0 to 47 eggs female-1 d-1, while no diurnal synchronous spawning behavior was observed. Under the spring bloom condition, E. bungii showed prey preference for less mobile and larger-sized prey (≥30 μm ESD) and bloom-forming diatom Thalassiosira spp. accounted for >80% of ingested carbon. In the laboratory, E. bungii was successfully reared from newly hatched nauplii to adult with the diatom, Thalassiosira nordenskioldi, as a food resource. Nauplii newly hatched from eggs reached the adult stage in ca. 150 days (5°C) with a sigmoidal developmental pattern and no sexual difference in development pattern. Starvation experiments indicated that the starved copepodids (C1-C4) became more vulnerable to high temperature with the progression of developmental stage, suggesting that the post-bloom condition with low food availability and increased temperature is harsh for their copepodids. The results of this study in conjunction with previous findings suggest that E. bungii is well adapted to utilize large-sized phytoplankton, such as a bloom-forming diatoms and, therefore, their recruitment processes, including egg production, development and mortality would be strongly affected by the duration and intensity of the spring bloom. © 2010 Springer Science+Business Media B.V.
Sekino M.,Tohoku National Fisheries Research Institute |
Kakehi S.,Tohoku National Fisheries Research Institute
Conservation Genetics Resources | Year: 2012
The importance of parentage analysis has been underscored in the conservation genetics. We present a software package for parentage allocation running in Microsoft ® EXCEL™, PARFEX (v1.0). It implements exclusion and likelihood-based methods based on microsatellite and/or SNPs markers. © 2011 Springer Science+Business Media B.V.
Kurita Y.,Tohoku National Fisheries Research Institute
Fisheries Research | Year: 2012
A generalized method to accurately estimate the spawning fraction (S) of multiple batch spawning fish considering the duration of histological spawning markers over a wide range of ambient temperature, spawning time frequency distribution of the population, and sampling time was developed. The concept of the variable "fraction of the daily spawning females with spawning markers at a sampling time t (FDSM t)", which varies diurnally in relation to the duration of the spawning markers and the spawning time frequency distribution, was introduced. Spawning fraction can be calculated as S=Psm t×(1/FDSM t), where Psm t is the observed fraction of active females with signs of previous or imminent spawnings, referring to various spawning markers, at a sampling time t. Simulations suggested the following two methods were robust when the spawning time frequency distribution was long and uncertain. The first refers to sampling females evenly throughout the 24h period, whilst the second is based on selecting a single or combination of spawning markers so that the total temperature-adjusted marker duration at sampling sums to around 24h and applying, if necessary, a correction factor. With these methods, the influence of sampling time and spawning time frequency distribution can be ignored. The utility of the second method was evaluated with field data for Japanese flounder Paralichthys olivaceus. In all cases, accurate validation of the temperature-dependent duration of spawning markers is essential for accurate estimation of S. © 2011 Elsevier B.V.