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Kawakami T.,University of Tokyo | Okouchi H.,Fisheries Research Agency | Okouchi H.,Head Office of Fisheries Research Agency | Aritaki M.,Fisheries Research Agency | And 3 more authors.
Fisheries Science | Year: 2011

The embryonic development and morphology of eggs and newly hatched larvae of the Pacific herring Clupea pallasii were described using laboratory-reared specimens originating from the Miyako Bay stock. The eggs were almost spherical in shape, 1.33-1.46 mm (mean: 1.38 mm) in diameter, and had a thick adherent chorion. They had a segmented pale yellow yolk, no oil globule, and a relatively wide perivitelline space. A subgerminal cavity was observed during the gastrula period, whereas the blastocoel did not appear. Mass hatching occurred by 271 h 45 min after fertilization, and the newly hatched larvae were 7.1-7.7 mm (mean: 7.5 mm) in total length with 53-56 myomeres at 9.6°C. The embryonic development of Pacific herring was substantially similar to that of zebrafish Danio rerio, American shad Alosa sapidissima, as well as Atlantic herring Clupea harengus, and generally followed the basic developmental pattern of teleosts. However, Pacific herring larvae hatched at a more developed stage than some other clupeoids, such as Japanese sardine Sardinops melanostictus, and the progressed developmental stage at hatching could be interpreted as an advanced adaptation. © 2010 The Japanese Society of Fisheries Science. Source


Shigenobu Y.,Japan National Research Institute of Fisheries Science | Fujimoto K.,Japan National Research Institute of Fisheries Science | Ambe D.,Japan National Research Institute of Fisheries Science | Kaeriyama H.,Japan National Research Institute of Fisheries Science | And 5 more authors.
Scientific Reports | Year: 2014

We measured the radiocesium (134Cs and 137Cs) contamination of 236 greenlings (Hexagrammos otakii) off the coast of Fukushima Prefecture in Japan, following the accident at the Fukushima Daiichi Nuclear Power Plant in March 2011. The radiocesium concentrations of greenlings caught approximately 40 km south of the power plant were significantly higher than those of greenlings caught approximately 50 km north of the power plant. The radiocesium concentrations of greenlings caught in southern waters were significantly higher in shallow than in deep waters. Meanwhile, two outlier specimens of greenlings with higher 137Cs concentrations, 16,000 Bq/kg-wet on 1 August 2012 and 1,150 Bq/kg-wet on 8 May 2013, were caught approximately 20 km from the power plant. Our calculations suggest that the probability of two such outlier specimens being found off the coast of Fukushima is exceedingly low. By contrast, extremely contaminated greenlings were frequently caught in the power plant port (geometric mean of 137Cs = 17,364 Bq/kg-wet). Our results suggest that the two outlier greenlings with higher 137Cs concentrations migrated from the power plant port. Continued close monitoring of radiocesium concentrations in the area should be done to ensure the safety of food supplies. Source


Fujimoto K.,Japan National Research Institute of Fisheries Science | Miki S.,Japan National Research Institute of Fisheries Science | Kaeriyama H.,Japan National Research Institute of Fisheries Science | Shigenobu Y.,Japan National Research Institute of Fisheries Science | And 7 more authors.
Environmental Science and Technology | Year: 2015

To clarify the level of contamination with radioactive cesium (radiocesium) discharged from Fukushima Dai-ichi Nuclear Power Plant (FDNPP), three fish species caught in the main harbor of FDNPP were subjected to γ-ray analysis. The concentration of radiocesium in muscle differed among individual fish, even those of similar size of the same species, and showed little relation to the standard length of fish. The maximum concentration of radiocesium (202 kBq/kg wet) was detected from fat greenling samples. A comparison to data from outside the port indicated that the level of radiocesium contamination inside the port was higher than that outside. We found that β-rays were emitted from otoliths of fishes caught in the port of FDNPP. β-ray intensities were correlated with the concentrations of radiocesium in muscles of the three fish species. In Japanese rockfish, the β-ray count rates from otoliths were significantly correlated with the concentration of radiocesium and 90Sr in the whole body without internal organs of Japanese rockfish. However, no β-rays were detected from brown hakeling samples collected around FDNPP, suggesting that the detection of β-rays from otoliths may indicate living in the main harbor of FDNPP. © 2015 American Chemical Society. Source


Ambe D.,Japan National Research Institute of Fisheries Science | Kaeriyama H.,Japan National Research Institute of Fisheries Science | Shigenobu Y.,Japan National Research Institute of Fisheries Science | Fujimoto K.,Japan National Research Institute of Fisheries Science | And 10 more authors.
Journal of Environmental Radioactivity | Year: 2014

The spatial distributions of radiocesium concentration in sea sediment to a core depth of 14cm were investigated in the offshore region from the Fukushima Prefecture to the northern part of the Ibaraki Prefecture in February and July 2012, at a spatial resolution of 5min of latitude and longitude. The concentrations in the area south of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) were generally higher than those in the area north of it. In the southern area, a band of especially high concentration with a width about 20km was present in the region shallower than 100m, and a narrow minimal concentration band was found along the 200-m isobaths. In more than half of all cases, the vertical core profiles of radiocesium concentration generally showed an exponential decreasing trend with depth. However, in the area north of the FDNPP, where the radiocesium concentrations tended to be very low, radiocesium concentrations that had similar or larger magnitude compared with those of the most-surface layer were often found in deeper layers. Relatively good correlations were found between radiocesium concentrations and grain sizes of the most-surface sediment. The vertical profile of radiocesium concentration also had a relationship with grain size. In other case, the radiocesium concentration in the sediment seems to have had a dependence on the radiocesium concentration in bottom seawater, suggesting that the quantity of radiocesium supplied and the grain size were major factors determining the spatial distribution pattern of the radiocesium concentration after the FDNPP accident. © 2014 The Authors. Published by Elsevier Ltd. Source

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