Aquaculture Science
Online ISSN : 2185-0194
Print ISSN : 0371-4217
ISSN-L : 0371-4217
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Displaying 1-6 of 6 articles from this issue
Original paper
  • Akito Taniguchi, Tomoki Kawagishi, Ayumi Tanaka, Shin-ya Takata, Takah ...
    2023 Volume 71 Issue 2 Pages 75-85
    Published: June 20, 2023
    Released on J-STAGE: June 20, 2024
    JOURNAL FREE ACCESS

    Rotifer production without contamination by undesirable organisms is important for obtaining high yields of healthy fish. In this study, we investigated the suitability of the biodegradable polymer poly(butylene succinate-co-adipate) (PBSA) for rotifer production, focusing on the effects of PBSA addition on the growth of rotifers (Brachionus plicatilis), Euplotes ciliates, and Vibrio bacteria. PBSA addition enhanced rotifer growth in the tested range of 0.5-50 mg/ml. This effect was dose-dependent; the higher the concentration, the greater the effect. The maximum intrinsic and daily growth rates were 0.519 and 68%, respectively, equivalent to or higher than those under optimal rotifer culture conditions. In contrast, inhibitory effects on Euplotes growth were observed at 1 mg/ml or higher concentrations of PBSA, in a dose-dependent manner. Though it remains unclear if PBSA directly inhibits the growth of Vibrio bacteria, culture water of well-grown rotifers had fewer Vibrio bacteria. PBSA addition demonstrated pH-decreasing and buffering functions; the pH value in rotifer-free culture water decreased from 7.9 to 6.7 after a 5-day incubation period and to 5.8 after a 10-day incubation period. This study demonstrates that the application of PBSA in aquaculture could enhance rotifer production while avoiding contamination by Euplotes and Vibrio.

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  • Motohiro Takagi, Naoki Kawata, Yuki Yamada, Yoichi Kawaguchi
    2023 Volume 71 Issue 2 Pages 87-98
    Published: June 20, 2023
    Released on J-STAGE: June 20, 2024
    JOURNAL FREE ACCESS

    Three water storage dams (the Kawaguchi dam, the Nagayasuguchi dam, and the Kominono dam at the downstream) were constructed in sequence along in the Naka River in Tokushima Prefecture, and the fishery association released multiple ayu seedlings. The purpose of this study was to elucidate the origin of ayu inhabiting the dam lakes of the Naka River by using microsatellite DNA markers that are effective for population analysis, and to contribute to appropriate resource management. Form discrimination showed that most but not all of the artificial seedlings released were derived from an amphidromous form, but genetic heterogeneity was confirmed in many of the seedlings. The ayu larvae and juveniles collected in the dam lakes of the Naka River were of amphidromous form, and no heterogeneity was confirmed with the natural seedlings from the Naka River downstream of the dam. On the other hand, for the larvae collected upstream of the Kominono dam at the end of October 2018, a population structure similar to that of a specific artificial seedling was confirmed.

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  • Yukina Tsujihara, Hirokazu Matsuda, Tohru Kasuya
    2023 Volume 71 Issue 2 Pages 99-109
    Published: June 20, 2023
    Released on J-STAGE: June 20, 2024
    JOURNAL FREE ACCESS

    We examined the effects of the different start timings of removal of oily water surface films (OWSF) on initial swim bladder inflation (SBI) and subsequent growth in cultured seven-band grouper. Hatched larvae were cultured under three conditions where OWSF were removed from 6, 8 or 10 days after hatching (DAH). The condition that OWSF were removed from 10 DAH is in practical use in the seed production of this species. The group to which the removal from 6 DAH was allocated had the highest SBI rate at the end of the experiment. Initial SBI was confirmed at 10 DAH in all groups, 4-5 days earlier than previously reported. These were probably caused by more rapid growth of larvae compared to before, suggesting that larval SBI possibly occurs at earlier timing, depending on culture conditions. It is necessary to adjust the start timing of removal of OWSF according to ongoing larval development. Total lengths (TLs) of individuals with inflated swim bladders (ISB) were not different from those without ISB until 20 DAH; afterwards, TLs of individuals with ISB were significantly larger than those without ISB, indicating that the presence or absence of ISB has an impact of the subsequent growth.

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  • Satoshi Katayama, Yueqiu Zhou, Koji Kawazu, Yutaka Kobayashi, Toshihir ...
    2023 Volume 71 Issue 2 Pages 111-114
    Published: June 20, 2023
    Released on J-STAGE: June 20, 2024
    JOURNAL FREE ACCESS

    Pen shell Atrina pectinata began to increase gradually in abundance in Tokyo Bay off Futtsu City in the 2000s supporting fisheries production. However, knowledge of the biology of this species remained inadequate for fisheries resource management. This study focused on revealing the annual reproductive cycle of the pen shell based on gonad maturation and spawning of individuals caught off Futtsu. A seasonal pattern of gametogenesis observed histologically indicates the spawning season is estimated from July to September. Additionally, indices of viscera and adductor weights peak from April to June when hypoxic water masses frequently occur at the fishing grounds. These findings suggest that spring hypoxic conditions could detrimentally affect reproduction of the pen shell population and its fisheries value.

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