Diet of Japanese eels Anguilla japonica in the Kojima Bay-Asahi River system, Japan

• Published in: Environmental biology of fishes 2013-04, Vol.96 (4), p.439-446
• Main Authors: Kaifu, Kenzo, Miyazaki, Sachie, Aoyama, Jun, Kimura, Shingo, Tsukamoto, Katsumi
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Anguilla japonica; Animal and plant ecology; Animal populations; Animal Systematics/Taxonomy/Biogeography; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Biomedical and Life Sciences; Brackish; Cambaridae; Carbon sources; Clarkia; Diet; Enrichment; Environment; Fish; Food resources; Fresh water ecosystems; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; General aspects; Habitats; Isotopes; Isotopic enrichment; Life Sciences; Marine; Nature Conservation; Nitrogen; Nitrogen enrichment; Prey; Procambarus; Rivers; Stable isotopes; Synecology; Upogebia major; Vertebrata; Zoology
• ISSN: 0378-1909; 1573-5133
• DOI: 10.1007/s10641-012-0027-0

The diet of Japanese eels, Anguilla japonica , was investigated using stomach content and stable isotope analyses. Stable isotope enrichment of carbon and nitrogen (Δδ 13 C and Δδ 15 N) was first estimated for A. japonica by comparing the isotopic signatures (δ 13 C and δ 15 N) of reared eels to that of their food. The estimated isotope enrichment was then applied to the diet estimation of A. japonica in the Kojima Bay-Asahi River system, Japan, combined with conventional stomach content analysis. Stable isotope enrichment varied among tissues, from 0.2‰ to 0.8‰ for carbon and from 1.3‰ to 2.1‰ for nitrogen. Nitrogen isotope enrichment of A. japonica muscle estimated in this study was 2.1‰, which was different from the previously reported mean δ 15 N enrichment of several animals of 3.4‰. These results indicate that isotope-based diet estimations for A. japonica need to use species- and tissue-specific values of isotope enrichment. In the diet analysis, stomach contents and stable isotopes revealed that (1) A. japonica appear to usually feed on a single type of prey species in each feeding session, (2) principal prey species were mud shrimp, Upogebia major , in brackish Kojima Bay and crayfish, Procambarus clarkia , in the Asahi River, (3) A. japonica in Kojima Bay primarily depend on the pelagic food web as a carbon source due to mud shrimp being filter feeders and eels in the Asahi River primarily depend on the littoral food web. Based on these results and the recently reported eel movements between Kojima Bay and the Asahi River, it appears that A. japonica can adapt to various feeding environments as opportunists, but also utilize the food resources by targeting a single type of prey species during a single feeding session.