Abstract: The narrow-clawed crayfish, Astacus leptodactylus for its natural characteristics has a strong ecological impact in Manyas Lake. The record of ectocommensalism between Epistylis sp. and A. leptodactylus has been observed in Turkey. The narrow-clawed crayfish in the gill-chamber and on the gill filaments, carapace, abdomen, walking legs, uropod, telson, antennae, antennulae and eggs are present a ciliate protozoa peritrich as Epistylis sp. The total of 1018 specimens was examined, 512 were involved in ectocommensalism as being 50,29%. The presence of the ectocommersal Epistylis sp. has been determined in a new locality from Manyas Lake in Turkey. The correlation between the ciliata and the crayfish, and the water quality are shown monthly.