NIPPON SUISAN GAKKAISHI
Online ISSN : 1349-998X
Print ISSN : 0021-5392
ISSN-L : 0021-5392
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Volume 74, Issue 2
Displaying 1-37 of 37 articles from this issue
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  • Factors responsible for the drastic catch decline of the Manila clam Ruditapes phillipinarum in Japan
    YASUO MATSUKAWA, NARITOSHI CHO, SATOSHI KATAYAMA, KOICHIRO KAMIO
    2008 Volume 74 Issue 2 Pages 137-143
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.137
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      The annual catch of the Manila clam Ruditapes phillipinarum in Japan increased from 100 thousand tonnes in 1960 to 140 thousand tonnes in 1982. This increase occurred despite a local decrease in coastal fishing grounds due to land reclamation and helped to balance overall production. Since 1984, however, the catch has decreased drastically to only 50 thousand tonnes and has remained at this low level. The authors reviewed published reports relevant to the ecology and resources of Manila clam and concluded that the main factor responsible for the drastic decrease in catch is over-fishing. Over-exploitation of the adults and sub-adults significantly affected and damaged reproduction and source-sink relationships among localities. Disturbance of the clam habitat throughout the year by heavy fishing gear may also be responsible for lowering the survival rate of the juveniles.
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  • Effects of hypoxia and hypercapnia on the embryonic development of striped jack, Pseudocaranx dentex
    YOSHIFUMI SAWADA, KAZUHIRO HIGUCHI, YUTAKA HAGA, KAZUHIRO URA, YASUNOR ...
    2008 Volume 74 Issue 2 Pages 144-151
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.144
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      The hypoxic condition, which sometimes occurs in the high-density layer of fish eggs during the procedures of egg collection and transportation in aquaculture, is thought to be accompanied by hypercapnia. This study investigated the effects of hypoxia and hypercapnia for the striped jack Pseudocaranx dentex embryos during somitogenesis. The somitic disturbances in newly hatched larvae were induced by the extreme hypoxia of exposure to 0% dissolved oxygen (DO) concentration for 30 and 60 minutes. Extreme hypercapnia of 120 mg/L dissolved carbon dioxide (DCD) concentration for 90 or 120 minutes also induced the disturbances. The moderate hypoxic condition of exposure to 25% DO concentration for 60 and 90 minutes accompanied with hypercapnia of exposure to 120 mg/L DCD concentration induced somitic disturbances whereas this hypoxic condition alone did not induce them. The incidence rate of somitic disturbances was higher in the case of hypoxia of 25% DO and hypercapnia of 120 mg/L DCD than that in the case of normoxia of 100% DO and hypercapnia of 120 mg/L. These results indicate that hypoxia and hypercapnia during somitogenesis induce somitic disturbances as in other marine fishes and their coincidence promotes the induction in striped jack.
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  • Winter distribution of young walleye pollock Theragra chalcogramma investigated with quantitative echosounder on the Pacific coast of eastern Hokkaido, Japan
    OSAMU SHIDA, HIROYA MIYAKE, TOMONORI KANETA, RYOTARO ISHIDA, KAZUSHI M ...
    2008 Volume 74 Issue 2 Pages 152-160
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.152
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      To understand winter distribution patterns of young walleye pollock Theragra chalcogramma and its determinants, we conducted an echo integration survey on the Pacific coast of eastern Hokkaido (the Doto area) in late February of 1998. Pollock aggregations were mainly located from the shelf edge to the continental slope region (150-400 m) with temperature ranging from 2 to 4°C. In contrast, the fish echoes were not present in the continental shelf region, which was dominated by the low temperature (<2°C) and low salinity (<33.0) Coastal Oyashio Water. Walleye pollock showed diel vertical migration patterns, involving staying near the bottom during the day and rising to the mid-water area at night. Our results show the fish's (1) offshore-ward movements and (2) concentrations in deeper water in winter. These observed pollock distribution changes were probably enhanced in marine environmental dynamics, caused by intrusion of the Coastal Oyashio Water into the shelf region. It is suggested that such distribution changes affect young pollock survival and are important for determining year class strength.
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  • In situ diameter measurement of Nomura's jellyfish Nemopilema nomurai by using a newly developed tool
    TORU YASUDA, MASAYA TOYOKAWA
    2008 Volume 74 Issue 2 Pages 161-165
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.161
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      We developed a tool for measuring the diameter of the Nomura's jellyfish Nemopilema nomurai, whose weight often exceeds 60 kg, without lifting them out of the seawater. Use of the newly developed tool made it possible to collect sufficient bell diameter data to enable analysis of the population growth. Change of diameter of jellyfish at set-nets of Mihama, Fukui Prefecture was monitored and compared with on-deck measurements during seven surveys from 4 September to 1 November, 2006; each survey measured 23-70 individuals by the tool and 5-31 individuals on deck. Comparison of the measurements found a significant difference in only a single survey out of the seven. This difference was probably because of bias in selecting the specimens to measure rather than any specific difference between the methods. According to the analysis of data measured by the tool, mean diameter was largest on the first sampling day, then decreased gradually to the end of September, and was rather stable in October with a slight increase at the end of the month.
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  • The relationship between the mucilage polysaccharides content and the sexual maturation of marine brown alga Akamoku Sargassum horneri collected in the Chikuzen Sea (Fukuoka Prefecture)
    RIEKO KURODA, KYOKO UEDA, TARO KIMURA, TETSUYUKI AKAO, NAOYA SHINOHARA ...
    2008 Volume 74 Issue 2 Pages 166-170
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.166
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      Previously, we reported on the seasonal variation of the mucilage polysaccharide content of Akamoku Sargassum horneri in the Chikuzen Sea (Fukuoka prefecture), and suggested a relationship between fucoidan content and sexual maturation of the alga. To confirm this finding, we conducted further investigations of the mucilage polysaccharide content depending on male-female difference and alga maturation stage, focusing on receptacles. It was found that most of the fucoidan is contained in receptacles, and the amount of fucoidan increases in the receptacle elongation stage, and decreases after the gamete releasing stage. These findings strongly suggest that fucoidan participates in the reproduction of Akamoku. Additionally, the sugar composition and the sulfated rate of fucoidans derived from Akamoku receptacles revealed that there is no notable difference in composition between male and female plants. Based on these results, we propose using the formation of receptacles as a criterion to decide the season for picking fucoidan-rich Akamoku alga.
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  • Patterns and frequency of hypermelanosis on the blind side in wild Japanese flounder
    TAKESHI TOMIYAMA, TAKUJI MIZUNO, MASATO WATANABE, TSUNEO FUJITA, GYOU ...
    2008 Volume 74 Issue 2 Pages 171-176
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.171
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      Hatchery-reared Japanese flounder Paralichthys olivaceus usually exhibit body color anomalies (hypermelanosis) on the blind side, which enable released fish to be distinguished from wild fish. Through our 54 fish market surveys carried out for 4 markets in Fukushima Prefecture, such body color anomalies were also found in wild fish with the frequency of 1.2%, i.e. 130 individuals of the total 10970 fish. Twenty-nine wild individuals had evident color anomalies and were recognized as the released fish at the markets. The color anomaly patterns of the wild fish were different from the released fish and were classified into five types. Dorsal ray counts, which largely differed between the wild and released fish in this area, were useful to confirm the discrimination between the wild and released fish.
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  • A study on the distribution of polyploid loaches in China
    YA-JUAN LI, JIE YIN, JA-BO WANG, XU YUAN, JIE WEI, XIAO-WEN SUN, KATSU ...
    2008 Volume 74 Issue 2 Pages 177-182
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.177
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      Natural triploid and asexually reproducing clonal diploid loaches are found in Japanese populations of the loach, Misgurnus anguillicaudatus. The distribution of polyploid loaches in Chinese populations has not been studied except for a few cytogenetic studies that described the occurrence of polyploidy. In the present study, we examined the ploidy status of a total of 762 specimens collected from 29 localities in China by measurements of erythrocytic cell nucleus after the ploidy determination performed by chromosome counting and DNA content flow-cytometry in selected individuals. Among diploid, triploid and tetraploid individuals, significant differences were detected in major and minor diameters of nucleus, and also nuclear volume. A few triploid (3n) loaches were detected in relatively wide areas including Hohhot, Neimenggu (3.3%), Tianjin (5.3%), Hangzhou, Zhejiang (3.3%), Chibi, Hubei (3.3%), Honghu, Hubei (6.7%) and Shashi, Hubei (3.3%). However, tetraploid (4n) loaches were detected only in Chibi (3.3%), Honghu (16.7%), Shashi (3.3%) and Ezhou (5.0%) from Hubei province. These results indicate that there are several localities in China exhibiting relatively higher frequencies of polyploid loaches.
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  • Genetic variability of wild and hatchery-released red sea bream in Kagoshima Bay, Japan, evaluated by using microsatellite DNA analysis
    HIROTOSHI SHISHIDOU, SHUICHI KITADA, TAKASHI SAKAMOTO, KATSUYUKI HAMAS ...
    2008 Volume 74 Issue 2 Pages 183-188
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.183
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      Genetic variability of natural and hatchery-released red sea bream in Kagoshima Bay and its vicinity was evaluated using three microsatellite DNA markers. Hardy-Weinberg equilibrium was found at all loci for each sample and even for all natural fish combined overall samples. Allele frequencies of IKB (natural fish caught in inner Kagoshima Bay) and hatchery-released fish caught in the bay were different from other natural samples. Observed mean heterozygosities and mean number of alleles per locus for IKB and natural fish caught in central Kagoshima Bay were high and similar to the results of previous studies for red sea bream. The results suggested that the large-scale hatchery releases for 30 years might influence the allele frequencies of IKB. However, the genetic diversity in the IKB has been maintained due to the large gene flow between the bay and its vicinity.
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  • Relationship between Microcystis morphospecies composition and nutrient concentration in the water basin (Nishiura, Kitaura) of Kasumigaura, Japan
    TAKAMITSU HOMMA, NOBUYUKI KOMATSU, MASAMI NEGISHI, KOYA NAKAMURA, HO-D ...
    2008 Volume 74 Issue 2 Pages 189-198
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.189
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      Influences of nitrogen and phosphorus concentrations on Microcystis morphospecies were confirmed from the results of an investigation of Lakes Nishiura and Kitaura between July and September 2005. During the exponential growth phase, the growth of the Microcystis population was limited by phosphorus (DIN: DIP>7) and M. aeruginosa was dominated in Nishiura. In Kitaura, the limiting factor for Microcystis growth was nitrogen (DIN: DIP<7) and four morphospecies of Microcystis, M. aeruginosa, M. ichthyoblabe, M. viridis and M. wesenbergii were observed. These results suggested that Microcystis morphospecies compositions were affected by nutrient concentrations in lake water.
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  • Contribution of walleye pollack frozen surimi components to physical properties of heat-induced gel formed from it
    SEIICHI KITAKAMI, YURIKO MURAKAMI, SATOMI KOSEKI, NOBORU KATO, KEN-ICH ...
    2008 Volume 74 Issue 2 Pages 199-206
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.199
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      The contribution of components in walleye pollack frozen surimi to the heat-induced gel formed from it was investigated. The proximate composition and breaking strength (BS) and breaking strain (bs) of the two-step heated gel formed were measured. The results were as follows: (1) On addition of water (0-125%) or sugar (0-50%) to the surimi, the maximum values of BS and Gs (BS/bs) of the heated gel formed were decreased, although the rate of decrease with sugar was larger than that with water. (2) When the protein concentration in the heated gels was fixed, the increase in sugar concentration from 6.1 to 24.5% caused the decrease in the maximum value of BS while that of Gs was unchanged. (3) When the concentrations of protein together with moisture in the heated gels were fixed, the reduction in the sugar concentration from 7.7 to 3.7% in the heated gel did not change the maximum values of BS and Gs. These results indicate that the physical properties of the two-step heated gel can be designed by regulating its proximate composition.
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  • Seasonal variation of the lipid content in the muscle and ecological traits of spotted mackerel Shimizu-Saba —When is Shimizu-Saba in season?—
    SHOKO ISOGAWA, KOSAKU YAMAOKA, KATSUJI MORIOKA
    2008 Volume 74 Issue 2 Pages 207-212
    Published: 2008
    Released on J-STAGE: March 23, 2008
    DOIhttps://doi.org/10.2331/suisan.74.207
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      We examined the seasonal variation of lipid content and ecological traits including gonad index of Shimizu-Saba, a population of spotted mackerel, caught off the Cape of Ashizuri. Sampling was conducted from December 2005 to November 2006. Fifteen fishes were collected in each month and were classified into 3 size classes: middle size 400-600 g (M), large size 600-900 g (L), extra large size 900 g or over (XL) (5 fishes were sampled from each size class in each month). The gonad index increased from December 2005 and attained the peak earlier in order of the size class (XL: January, L: February, M: March). Lipid content of the dorsal muscle showed a common seasonal change in the three size classes, decreasing from winter to spring and increasing from autumn to winter. The first decrease in lipid content of M and XL sizes was observed at the time of maturity and the early spawning season, respectively. After the spawning season, the lipid content increased. Comparing the rate of lipid given in autumn-winter with that in spring-summer, the former clearly showed higher content, suggesting that Shimizu-Saba is in season in autumn and winter.
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