Sheng Bi

Long-term changes in land-use and water quality degradation are key pressures on riverine ecosystems, yet their effects on the functional structure of fish assemblages remain insufficiently quantified. We conducted a decadal assessment of fish assemblages in four rivers experiencing rapid land-use transformation in Guangxi, China—the Zuojiang (ZY), Youjiang (YJ), Yujiang (YuJ), and Guijiang (GJ) rivers. Species-level functional traits describing body shape, vertical habitat position, feeding guild, trophic level, and maximum total length were used to calculate multiple functional diversity indices related to environmental variables using redundancy analysis and random forest models. Over the decade from 2013 to 2023, impervious surface and bare land increased significantly, while forest, shrubland, and grassland declined, coinciding with marked deterioration in water quality, including higher chlorophyll-a and lower dissolved oxygen concentrations (p < 0.05). Fish abundance and species richness decreased, and formerly dominant benthic cyprinids and loaches were replaced by tolerant and invasive taxa such as Oreochromis niloticus and Tilapia zillii. NMDS and PERMANOVA indicated a significant shift in community composition between 2013 and 2023 (R² = 0.14, p < 0.001), with fish assemblages shifting toward small-bodied, pelagic, omnivorous, and laterally compressed species. Functional richness declined, whereas functional evenness and functional dispersion increased, indicating functional simplification and homogenization. Multivariate and machine learning models consistently identified increasing impervious cover and declining dissolved oxygen as the strongest predictors of these changes. Our results demonstrate that land-use intensification and water quality deterioration are associated with reduced functional integrity in Guangxi rivers and highlight the value of trait-based indicators for monitoring and managing biodiversity in rapidly urbanizing catchments.

Fish occupy pivotal trophic positions in aquatic ecosystems, mediating energy transfer and shaping community structure through their feeding interactions. Unraveling these dietary relationships is therefore fundamental for understanding ecosystem functioning and supporting sustainable fisheries management. Traditional morphological analyses, while informative, often fall short in resolving fine-scale prey diversity and trophic linkages. In contrast, DNA metabarcoding has revolutionized dietary studies by enabling comprehensive, high-resolution, and non-invasive characterization of prey assemblages. This review synthesizes recent progress in applying DNA metabarcoding to fish trophic ecology, emphasizing technical innovations, methodological standardization, and ecological insights. We discuss how DNA metabarcoding has advanced the understanding of food web complexity, species interactions, and ecological responses to environmental change. However, challenges persist in quantification accuracy, reference database completeness, and cross-source contamination. Future research integrating multi-marker approaches, standardized workflows, and multi-method integration holds promise for transforming DNA metabarcoding into a powerful, reliable and mechanistic tool for trophic ecology. Collectively, these developments will bridge molecular data with ecological theory, strengthening the scientific foundation for ecosystem-based fisheries management.