Aquaculture Science
Online ISSN : 2185-0194
Print ISSN : 0371-4217
ISSN-L : 0371-4217
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Volume 69, Issue 3
Displaying 1-8 of 8 articles from this issue
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Original paper
  • Increasing fisheries catch and life history traits of searobin Lepidotrigla microptera off Miyagi Prefecture
    Yuriko Okamura, Satoshi Katayama, Yuki Okuno, Xitong Yang, Yoshio Mas ...
    2021 Volume 69 Issue 3 Pages 177-184
    Published: 2021
    Released on J-STAGE: September 20, 2022
    DOIhttps://doi.org/10.11233/aquaculturesci.69.177
    JOURNAL FREE ACCESS
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    Commercial fisheries stocks of the searobin Lepidotrigla microptera collected off Miyagi Prefecture by set net and bottom trawl started increasing gradually in 2006, and eventually exceeded 300 tons in both 2016 and 2017. Gompertz growth formulae estimated by the age determination using otoliths showed a significant difference between male and female. The asymptotic total lengths of males and females were 252 mm and 279 mm, respectively, and it was found that females grew larger. The total length and age at maturity were estimated to be 230 mm at 3+ years for males, and 250 mm at 3+ years for females. The gonad weight index peaked in June and decreased rapidly from July to August; this is in accordance with searobin spawning season which occurs in Miyagi prefecture from June to August. No predominate age group was identified from the age composition, but with individuals aged 4+ years accounting for the majority of examined searobins, it is fathomable that individuals of the 2015 age-class and earlier had already spread out. Taken together, these results suggest that environmental conditions in Miyagi waters have improved over the past decade and, consequently, have possibly attributed to increased recruitment of searobins.
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  • Prey selectivity of red stingray Hemitrygon akajei caught in the small scale set net installed in estuary
    Kaito Suzuki, Keiko Yamaguchi, Mikio Nakamura
    2021 Volume 69 Issue 3 Pages 185-193
    Published: 2021
    Released on J-STAGE: September 20, 2022
    DOIhttps://doi.org/10.11233/aquaculturesci.69.185
    JOURNAL FREE ACCESS
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    The red stingray Hemitrygon akajei is a predator increasing in abundance in Japan’s coastal areas and estuaries. However, few studies have revealed the impact of increased red stingrays on ecosystems and fisheries. This study elucidates the prey selectivity of red stingray in the small scale set net and estimates its impact on fishery in estuaries. Prey items that preyed on by red stingrays in the set nets were identified from the digestion level. Four species, Sardinella zunasi, Engraulis japonicus, Nuchequula nuchalis, and Metapenaeus ensis, were thought to be preyed upon inside the set nets. The red stingrays tend to prey on dead or weak fish; however, the prey selectivity for M. ensis was higher than that for other species despite the low catch of M. ensis. Thus, these results indicate that in estuaries, the red stingray is a harmful predator of M. ensis in the set-net fishery.
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  • Effects of somatic growth and insulin-like growth factor mRNA expression in the liver of salmon by feeding with sugarcane bagasse extract
    Shunsuke Moriyama, Kiyoaki Miyasaka, Toma Furuta
    2021 Volume 69 Issue 3 Pages 195-202
    Published: 2021
    Released on J-STAGE: September 20, 2022
    DOIhttps://doi.org/10.11233/aquaculturesci.69.195
    JOURNAL FREE ACCESS
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    We examined the ability of sugarcane bagasse extract (SBE) to accelerate the somatic growth and insulin-like growth factor-I (IGF-I) mRNA expression of rainbow trout Oncorhynchus mykiss and coho salmon Oncorhynchus kisutsh. Those fed pellets containing 100 mg and 500 mg/kg SBE showed significant increases in body weight compared with the control. Higher IGF-I mRNA levels in the liver at the end of sampling time was observed in fish fed pellets containing 100 mg and 500 mg/kg of SBE. No change in body weight and hepatic IGF-I mRNA expression was observed following a feeding pellet with 1,000 mg/kg SBE. Incubation of the liver pieces with DDW-extracted SBE at concentrations of 100 and 200 µl/ml for 24 hr at 15°C resulted in a concentration-dependent increases in IGF-I mRNA expression. These results suggest that SBE might be enhanced IGF-I mRNA expression in the liver, and subsequently improved somatic growth of rainbow trout and coho salmon.
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  • Differences in free amino acid compositions in liver and dorsal white muscle of juvenile Pacific bluefin tuna Thunnus orientalis fed raw fish and artificial feeds
    Takeshi Yamamoto, Hiroshi Hashimoto, Koji Murashita, Hiroyuki Matsunar ...
    2021 Volume 69 Issue 3 Pages 203-211
    Published: 2021
    Released on J-STAGE: September 20, 2022
    DOIhttps://doi.org/10.11233/aquaculturesci.69.203
    JOURNAL FREE ACCESS
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    To develop a more efficient tuna feed, free amino acid compositions in the liver and dorsal white muscle of juvenile Pacific bluefin tuna Thunnus orientalis fed raw fish (RF) and commercial artificial feeds (AF) were compared. Hatchery-reared juveniles (initial BW, 2 g) stocked in two net cages were fed either of the foods from late July to mid-March, and fish samples for analysis were taken monthly. In the liver, concentrations of taurine were higher in the AF group, but increased in both groups toward autumn while concentrations of other amino acids decreased. In the muscle, histidine was dominant and its concentrations were higher in the RF group whereas concentrations of anserine and carnosine were higher in the AF group. In both the liver and muscle, levels of moisture were higher and those of crude fat lower in the AF group. Daily food intake (% monthly average BW/day) in the AF group was estimated to be as high as in the RF group. These findings suggest that dietary lipid utilization was not efficient in tuna fed the artificial feeds and instead dietary protein was used as an energy source, which resulted in the differences in muscle free imidazole-compound compositions.
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  • Size at sexual maturity and annual reproductive cycle of male crimson sea bream Evynnis tumifrons off the southwestern coast of Kyushu, Japan
    Lindon Havimana, Yasuji Masuda, Jun Ohtomi
    2021 Volume 69 Issue 3 Pages 213-222
    Published: 2021
    Released on J-STAGE: September 20, 2022
    DOIhttps://doi.org/10.11233/aquaculturesci.69.213
    JOURNAL FREE ACCESS
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    Size at sexual maturity and annual reproductive cycle of male Evynnis tumifrons were investigated off the southwestern coast of Kyushu, Japan. A total of 788 testes were examined histologically. Testis maturity stages were classified into six categories based on the appearance of the most advanced germ cell stage along with the presence of earlier spermatogenic stages, the amount of interstitial tissue, the presence of sperm within lobular lumen and efferent duct, and tunica thickness as follows: immature, developing, early maturing, late maturing, spent, and resting. Males with the testes at developing, early maturing, late maturing, and spent stages were defined as sexually mature, and the size at sexual maturity was estimated as 169 mm in fork length based on 50% maturity size. Monthly changes in the gonadosomatic index and the occurrence of individuals having testes at early maturing or late maturing stages showed that the period when mature fish release sperm was from October to May. Seasonal changes in the condition factor tended to be high from June to October.
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