To determine the biological diversity of the fishes of the Eyvashan River, between the Eyvashan Dam and the connection to the Kahman River branch, sampling operations were carried out during autumn and winter. In this study, 872 pieces of fish belonging to 5 families, 17 genera, and 20 species were caught using castanet, and electrofishing. 8 species were exotic that entered this river mainly due to aquaculture activities, and 12 species were native. There is no statistical information on warm-water exotic fishes. According to the descriptive statistics of fishing, the highest relative frequency belongs to the Alburnus caeruleus (21.58%), Cyprinion macrostomum (14.12%), Alburnoides nicolausi (14.12%), and Capoeta aculeata (12.74%), and the lowest frequency The ratio was related to Pseudorasbora parva (0.11%), Oncorhynchus mykiss (0.11%), Carassius auratus (0.22%) and Mastacembelus mastacembelus (0.22%). Ten species were evaluated with economic value, 8 species with sport fishing value, and 7 species with ornamental value.