Estimating Fish Population Size Using eDNA: The Case of Karataş Lake

The study focused on three economically and ecologically important target species, Cyprinus carpio , Carassius gibelio , and Sander lucioperca , in Lake Karataş, which was selected as the study area. Fieldwork was conducted during seasonal periods covering February, April, June, and September. eDNA samples were collected from three different stations in the lake, and abundance and biomass data of the species were simultaneously obtained using traditional fishing methods. In addition, simulation experiments were designed in a laboratory environment to separately evaluate the factors affecting eDNA concentration: fish number, water temperature, and exposure time. For this purpose, fish were kept in 250-liter fiber aquariums for 1, 2, 3, 6, and 9 days under different temperature conditions (7°C, 15°C, and 25°C) and with different numbers of individuals (1, 5, 10, 25). At the end of all experiments, a total of 192 water filters (0.22 µm) were obtained, and DNA extractions were performed using an optimized eDNA isolation protocol. Two-stage PCR was performed using universal fish primers MiFish-UF/MiFish-UR, and a high-throughput sequencing platform providing an average of 500,000 reads per sample was used. According to the bioinformatics analysis results, significant correlations were found between eDNA copy numbers and fish biomass and abundance estimated by conventional methods. In biomass/abundance estimates of target species, only an average deviation of 4% was observed between eDNA and conventional methods. These results demonstrate that the eDNA metabarcoding approach can offer a faster, more cost-effective, and more reliable alternative to conventional methods in monitoring fish populations in natural waters.