Tenagi Philippi, an area of high fishfauna biodiversity and high human pressure.

This study provides an updated inventory of fish species diversity, examines co-occurrence patterns of fish communities, and evaluates ecological water quality using the Fish-based River Integrity Index (FRII) at Tenagi Philippi, a biodiversity hotspot in Northern Greece. Tenagi Philippi, a unique peatland and agricultural landscape, is recognized for its high endemism, including endangered species such as Cobitis punctilineata and Caspiomyzon hellenicus. Sampling was conducted across 16 stations from 2022 to 2023, resulting in the identification of 18 species. Endemic species showed that their distribution patterns were linked to specific substrate and water quality conditions. Fish co-occurrence networks exhibited overall stability, with two native species, Barbus strumicae and Squalius orpheus, being the center of fish communities. The FRII analysis indicated that while one station exhibited "Good" ecological quality, most were rated "Moderate" or "Poor," largely driven by agricultural runoff and habitat fragmentation. These findings underscore the urgent need for targeted conservation efforts, continuous monitoring, and local engagement to safeguard these ecosystems.