Abstract
Aim Biological invasions are widely recognised as a major driver of global change, yet their mechanisms and impacts remain unevenly quantified across ecosystem dimensions. Freshwater ecosystems, among the most threatened worldwide, offer a critical arena to test invasion theory, from Elton's hypothesis on biotic resistance to contemporary models of trophic cascades and ecosystem regime shifts. Here, we aim to quantify the global impacts of invasive freshwater fish on biodiversity and ecosystem functioning across multiple trophic levels and to identify patterns related to invader feeding strategy and ecosystem sensitivity. Location Global; freshwater ecosystems worldwide. Time Period 1986–2024. Major Taxa Studied Freshwater fish, amphibians, macroinvertebrates, macrophytes, zooplankton, phytoplankton and periphyton. Methods Synthesis of 149 published studies encompassing 1055 invasion cases. A multi‐level mixed‐effects meta‐analysis was used to assess invasion impacts across seven aquatic functional groups, accounting for cross‐trophic interactions and invader feeding strategy. Results We show that invasive fish consistently depress abundance and diversity of native fish, amphibians and macroinvertebrates, while reducing macrophytes and zooplankton through resource competition and habitat alteration. In parallel, invasive species can trigger trophic cascades and bioturbation processes that stimulate phytoplankton and periphyton proliferation, pushing ecosystems across ecological thresholds towards alternative turbid and eutrophic stable states. Impacts pathways differ according to invader feeding strategy: omnivorous cyprinids often function as ecosystem engineers with broad ecosystem‐level effects, whereas carnivorous salmonids primarily alter communities through top‐down suppression. Main Conclusions By identifying taxa that respond consistently to fish invasions across trophic levels (fish, amphibians, macroinvertebrates, macrophytes) and by highlighting omnivorous and carnivorous invaders as key drivers of ecosystem restructuring, our findings link invasion dynamics to predictable freshwater regime shifts. This study provides a mechanistic framework linking invasion ecology, trophic cascades and ecosystem transitions, with important implications for biodiversity conservation and ecological restoration under accelerating global change.