One of the most important data in terms of sustainable fisheries is estimated fish population size. However, estimate the population size particularly in aquatic ecosystems is very difficult due to the complex miCrohabitat, vegetation, etc. and doesn’t give accurate results. İn the estimate of fisheries population size; virtual population size (VPA), removal method (Leslie population estimates), hunting method with gillnets, scanned/filtered field method and hydroacoustic methods are used. There are advantages and disadvantages when commonly used these methods are compared to each other. Generally, require quite a long sampling process and intensive labor. In recent years, environmental DNA (eDNA) has been used for determination of the distribution of aquatic vertebrate species in the reservoirs. In the aquatic environment, eDNA method which is an effective method for the determination of the presence of species and population size, gives results in a short time with high accuracy and low cost.