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[Nagano University Press Release] Meta-analysis on the Genetic Structure of Anguilla Eels Published in the International Journal Fish and Fisheries —Strengthening the Scientific Basis for Managing Anguilla Eels, Including the Japanese Eel, as a Single Stock—

IFB

On July 7, 2025, a research paper from the Institute of Freshwater Biology, Nagano University, was published in the international academic journal Fish and Fisheries, presenting a meta-analysis of the genetic population structure of the genus Anguilla (https://doi.org/10.1111/faf.70007).

Highlights of the Study

  1. Conducted a literature review of 66 studies on the genetic structure of Anguilla eels and performed a meta-analysis by extracting the means and standard deviations of pairwise genetic differentiation indices such as FST.

  2. Confirmed panmixia (a single interbreeding population) for most Anguilla species except Anguilla marmorata, although further research is required for some understudied species.

  3. Through meta-regression, examined how genetic marker types, differentiation indices, sample sizes, and sampling ranges influenced the detection of genetic differentiation, and emphasized the importance of ensuring sufficient sample sizes and representative sampling areas in future studies.

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Background

Eels of the genus Anguilla are widely distributed in rivers and coastal areas worldwide and are important fishery resources in terms of food culture and economy. In particular, the Japanese eel (Anguilla japonica) has faced severe declines in catch volume, posing a major issue both domestically and internationally. A fundamental component of eel resource management is understanding whether populations are structured into multiple subpopulations or form a single stock shared across national and regional boundaries.

Purpose of the Study

This study aimed to statistically synthesize and analyze results from previously published genetic studies using meta-analysis techniques, and to systematically review and test whether the genus Anguilla exhibits panmixia (a single genetic stock). The goal is to strengthen the scientific basis for sustainable freshwater eel resource management.

Methods

A total of 66 relevant domestic and international studies were reviewed, extracting FST values and other indicators of population genetic structure. Meta-analyses were conducted to estimate overall effects and test heterogeneity, considering factors such as genetic marker types and the geographic scope of sampling.

Main Findings

The analysis confirmed that most Anguilla species form genetically mixed, panmictic populations. In particular, the Japanese eel (Anguilla japonica) can be managed as a single stock across its entire distribution, including rivers and coastal areas within and outside Japan. Conversely, Anguilla marmorata showed clear regional genetic differentiation, indicating the presence of subpopulations. The study also highlighted the lack of research on tropical eel species and emphasized the importance of representative and extensive sampling to detect genetic differentiation accurately.

Significance and Future Outlook

This research, published in the internationally recognized journal Fish and Fisheries, makes a significant scientific contribution to advancing our understanding of the genetic structure of Anguilla eels. The confirmation of panmixia provides a stronger scientific foundation for managing eels as a single international stock. Future research is expected to address gaps in data for tropical eel species, clarify their genetic diversity and distribution patterns, and incorporate new technologies such as environmental DNA surveys. Continued monitoring, especially in the context of potential range expansions due to climate change, is also recommended.

Activities of the Institute of Freshwater Biology

The Institute of Freshwater Biology, Nagano University, serves as a core institution for large-scale projects funded by the Fisheries Agency, promoting research aimed at the sustainable use and conservation of eel resources, including the Japanese eel. Its initiatives encompass extinction risk assessments, analysis of genetic diversity, satellite tagging of spawning migrations, and field surveys on yellow and silver eels’ sex ratios. The Institute will continue collaborating with domestic and international research institutions and fisheries stakeholders to propose and implement evidence-based resource management strategies, further advancing research on the conservation and management of Japanese eels.

Acknowledgments

This research was conducted under the Fisheries Agency’s Fisheries Resource Survey and Assessment Promotion Project (Eel Unit).

Article Information

Contact

Institute of Freshwater Biology, Nagano University
Email: ifb@nagano.ac.jp
TEL: +81-268-22-0594
FAX: +81-268-22-0544
Contact: Hiroshi Hakoyama