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Nagasaki-shi, Japan

Dan S.,Fisheries Research Agency | Hamasaki K.,Tokyo University of Marine Science and Technology
Aquaculture International | Year: 2011

We investigated the effects of feeding rotifers containing various levels of n-3 highly unsaturated fatty acids (n-3HUFA) to Scylla serrata larvae at different developmental stages on their survival, development, and morphogenesis when they were cultured at six salinity levels. The first-, third-, and fifth (last)-stage zoeae and megalopae were reared to first-stage crabs at salinities of 10, 15, 20, 25, 30, and 35‰, with three different feeding regimes of rotifers containing different levels of n-3HUFA. The larvae successfully developed to the subsequent stages at 20-35‰ salinity. The highest survival rates to first-stage crabs were recorded at 20-25‰ salinity. The morphological features of the megalopa observed in the last-stage zoeae, represented by the ratio of the chela length to carapace length, tended to advance with increasing salinity, indicating higher assimilation efficiency at higher salinities. The megalopal features of the last-stage zoeae were enhanced when the larvae were fed rotifers containing higher amounts of docosahexaenoic acid (DHA). As reported previously, final-stage zoeal larvae with advanced megalopal features often experienced moult death syndrome (MDS). These results show that when larvae are fed rotifers with high DHA under high-salinity conditions, morphogenesis is accelerated, resulting in MDS. Therefore, to evaluate the effects of salinity on larval survival, it is necessary to examine larval morphogenesis in terms of MDS. In conclusion, we recommend that not only survival but also larval morphogenesis should be examined when evaluating the results of rearing experiments with S. serrata larvae. © 2010 Springer Science+Business Media B.V. Source

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. Source

Masuma S.,Fisheries Research Agency | Takebe T.,Seikai National Fisheries Research Institute | Sakakura Y.,Nagasaki University
Aquaculture | Year: 2011

We reviewed research on the broodstock management and larviculture of the Pacific northern bluefin tuna (PBT) Thunnus orientalis in Japan. Japan has been at the forefront of PBT research since 1970 due to the participation by federal and prefectural governments and universities in a national project aimed to optimize productivity of the sea around Japan. In 1979, scientists at Kinki University succeeded in the first spontaneous spawning in captivity by the broodstock of 5. year-old PBT. Successful spawning was also performed in 1980 and 1982, but no spawning then occurred until 1993, when Maruha Nichiro Holdings, Inc. (MNH) and Nippon Formula Feed Manufacturing Company, Ltd. (NFFMC) became involved in tuna farming and succeeded in the spawning of four-year-old broodstock. Since then, successful spawning of PBT in captivity has been reported from several sites as well as spawning in Kinki Univ. since 1994. With the successful spawning of PBT, the Fisheries Research Agency (FRA; formerly, Japan Sea Farming Association) of Kinki University, in conjunction with MNH, NFFMC, and Takuyo Ltd., has actively carried out research on and development of tuna larviculture technology. Thus, knowledge about broodstock management and larviculture has accumulated in Japan, but technical problems with larviculture still remain to be solved. There are 9 sites of successful spawning in net pens in Japan so far. At 4 of these sites in regions around Amami Island, yearly spawning has stably occurred. We have been accumulating data about the period of maturation, environmental key factors triggering the spawning, the age of onset of spawning, and the pattern of spawning through measurement of the ambient environment, gonad morphometry, endocrinology, mitochondrial DNA analysis, and daily careful observation of broodstock. Research on PBT larviculture at Kinki University, FRA, MNH, NFFMC, and Takuyo have succeeded in producing tens of thousands of hatchery-raised juveniles. As a result, Kinki University succeeded in establishing the full life cycle of PBT in captivity, and also achieved its aquaculture life cycle. However, solutions are needed for the remaining technological issues of PBT larviculture, including sinking syndrome, where larvae die on the bottom of the tank during the early phase of larviculture, the search for appropriate food (species, size, and nutrition) around the transition stage from larva to juvenile, cannibalism and collision against walls in the juvenile, and malformation and viral diseases in the young stage. © 2010 Elsevier B.V. Source

Takahashi H.,Fisheries Research Agency
New Ergonomics Perspective - Selected Papers of the 10th Pan-Pacific Conference on Ergonomics | Year: 2015

The number of Japanese fishermen is decreasing rapidly and those remaining are aging. According to the Food and Agriculture Organization, the number of fishermen in Japan is rapidly declining in contrast to those of other major fishing countries increasing or leveling off. One reason is thought to be the poor work environment. Although many Japanese fishing boats were mechanized in the last quarter of the twentieth century, most of the effort was directed at maximizing their catch efficiency, not improving their work environments. Therefore, fishing is still one of the hardest occupations in Japan. This study compared three case studies conducted in small trawl fisheries during actual work. The times required for the main tasks were measured, revealing that fish sorting was the most timeconsuming task in all cases. The physical burdens of the main tasks were estimated using the Ovako Working-posture Analyzing System (OWAS), the simplest, best-known method for judging the demands of tasks based on work postures. The results of the OWAS analyses varied with the tasks and cases. Regardless, fish sorting imposed a large physical burden when performed on deck. Use of a table appears to be a simple solution to improve work posture. © 2015 Taylor & Francis Group, London. Source

Morita K.,Hokkaido National Fisheries Research Institute | Nagasawa T.,Fisheries Research Agency
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2010

We examined latitudinal variation in riverine growth and parr maturation of an endemic Asian salmonid, masu salmon (Oncorhynchus masou), in 12 rivers located between 36.6°N and 45.4°N. Masu salmon parr showed considerable variation in growth and maturation patterns among populations. Body sizes were generally larger, and parr maturation was common at southern latitudes. Male parr matured at smaller sizes at more southern latitudes. Latitudinal variation in riverine growth and maturation of masu salmon parr was largely attributed to latitudinal changes in temperature and population density. Parr size at age increased with increasing temperature and decreased with population density. Riverine growth conditions were an important environmental factor determining parr maturation for both males and females; however, the occurrence of mature female parr required extremely favorable growth conditions. Water temperature in May, approximately four months before maturation, was the most important environmental factor affecting the maturation of male parr. Our study supports the hypothesis that freshwater residency was promoted by favorable growth conditions at southern latitudes. Source

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