Abstract
The European Water Framework Directive (WFD) 2000/60/EC emphasizes the use of fish communities as key indicators for assessing the ecological quality of freshwater ecosystems. Despite over two decades of WFD implementation, many Balkan countries lack standardized ecological assessment indices, particularly for fish fauna. This situation complicates efforts to monitor and manage aquatic ecosystems, especially transboundary waters facing significant environmental pressures. In this context, our study assesses fish communities and ecological quality in Lake Dojran, a transboundary lake shared by Greece and North Macedonia. Fish sampling was independently conducted by each country (North Macedonia in 2021 and Greece in 2023), using benthic multi-mesh gillnets following standardized European methodologies (CEN 2005). A total of 12 out of 16 historically recorded fish species were confirmed. Higher catch per unit effort (CPUE) values were observed in 2021 (282.50 specimens/gillnet, biomass 6321.81 g/gillnet) compared to 2023 (207.83 specimens/gillnet, 2378.67 g/gillnet). Dominant species included Alburnus macedonicus and Perca fluviatilis. No significant differences were found in CPUE values based on either number of specimens (NPUE) or biomass (BPUE) across the different depth zones. Using the Greek Lake Fish Index (GLFI), ecological quality based on fish fauna was classified as “good” in 2021 and “high” in 2023, reflecting the low relative contribution of both introduced numerical abundance and omnivorous species biomass in total catches. This study contributes valuable baseline data for transboundary ecological management and conservation strategies, supporting efforts aligned with WFD objectives.