Ecological role of ayu, common herbivorous fish, within a riverine biological community

2022 Fiscal Year Final Research Report

• Project/Area Number: 18H02267
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 40030:Aquatic bioproduction science-related
• Research Institution: Nagasaki University
• Principal Investigator: IGUCHI Keiichiro 長崎大学, 水産・環境科学総合研究科(環境), 教授 (00371865)
• Co-Investigator(Kenkyū-buntansha): 阿部 信一郎 茨城大学, 教育学部, 教授 (40371869) ; 竹門 康弘 京都大学, 防災研究所, 准教授 (50222104)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 生物多様性 / 河川生態系 / アユ / 付着藻類 / 水生昆虫 / 安定同位体比解析

Outline of Final Research Achievements

The purpose of this study is to elucidate the role played by the ayu Plecoglossus altivelis, which scrapes and eats attached algae on riverbeds, in river ecosystems. Through stable isotope ratio analysis, in the Kamo River in Kyoto City, which is located in a temperate zone, the biomass of attached algae decreases as the population density of ayu increases while food spillage after grazing and feces containing undigested algal cells were provided as a source of the fine particulate organic matter (FPOM) that is available as feed materials. Furthermore, it was shown that the FPOM derived from the feeding behavior of ayu also affected the food web of benthic animals such as aquatic insects. On the other hand, in Yakugachi River of Amami-oshima Island, which is in the subtropical zone, algae productivity is lower than in the temperate zone, and no relationship was detected between the diet of Ryukyu-ayu and the algae-derived substances contained in POM.

Free Research Field

保全生態学

Academic Significance and Societal Importance of the Research Achievements

アユは，摂餌縄張りを形成し，一定空間の防衛行動を通じて，付着藻類を排他的に利用するという見方が一般的であった。一方で、日本の淡水魚類相を代表するコイ科の魚類では、上下の顎に歯がないため、付着藻類を効率的に利用することはできない。本研究を通じて、摂餌の際のアユの食べこぼしや生きた藻類細胞を含む糞が微粒状有機物（FPOM）となり、他の魚類や水生昆虫に利用可能な餌料として供給されている実態が判明した。すなわち、アユの存在が、河川生態系における多種の共存に貢献していることになる。また、全国各地で、増殖目的で実施されてきたアユの種苗放流について、生物多様性の維持に資する新たな機能を追加することができる。