Urban aquatic habitats as refugia for threatened freshwater fish: Insights from the Corfu killifish

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Abstract Freshwater biodiversity is under immense pressure globally, with invasive species among the primary drivers of extinction risk. We tested whether urban aquatic habitats can serve as refugia for threatened freshwater fish from invasive species' pressure, focussing on the translocation of a critically endangered killifish (Corfu killifish, Valencia letourneuxi ) to a spring‐fed peri‐urban pond in northwestern Greece. Urban habitat suitability was assessed using the REVIVE‐POLIS feasibility analysis tool, which incorporates conventional ecological criteria (water and biological quality, species‐specific habitat requirements, and invasive species pressure) alongside urban‐specific criteria including hydrological stability, food web structure and surrounding land use. The tool supported the suitability of the release site and indicated its utility in urban conservation planning. The translocation involved a two‐stage transfer of a total of 84 adult killifish spawners into the recipient pond across 2021 and 2022, corresponding to an estimated introduction density of 1.12 translocated inds m −2 . Post‐release monitoring in 2022 utilizing electrofishing confirmed establishment at the release site (density 0.83 inds m −2 ), as evidenced by the presence of larvae and juveniles. Subsequent monitoring in 2024 and 2025 using underwater cameras recorded cohorts of approximately 30 individuals (density 0.71 inds m −2 ). These spanned multiple age classes on both occasions, suggesting persistence and recruitment for ≥3 years after the initial release. As a single‐site case study, these findings should be interpreted cautiously; nevertheless, they indicate that carefully selected and managed urban aquatic refugia may complement conventional approaches for threatened fishes exposed to invasive species, provided key constraints (biosecurity, habitat area and long‐term viability) are addressed. Practical implication . This study delivers a user‐ready feasibility assessment tool that helps practitioners identify urban aquatic habitats suitable as refugia for threatened fish, provides methodological guidance for designing, implementing, and monitoring threatened‐fish translocations, and shows that where invasive‐species eradication is unfeasible, well‐managed urban refugia can complement or in some contexts, substitute for conventional in situ translocations.

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