Topmouth Gudgeon Pseudorasbora parva (Cyprinidae) and Amur Sleeper Perccottus glenii (Odontobutidae) Are Alien Fish Species of the Ural River

The article presents new information about the distribution of two alien Asian fish species in the Ural River. The topmouth gudgeon Pseudorasbora parva observed for the first time in the river basin was recorded only at several locations along a 300-km section between the mouths of the Kolpachka and Urtaburtya rivers, which apparently is due to its relatively recent invasion. The species could have entered the river from fish farms, in which its appearance was the result of an accidental introduction together with phytophagous fishes. Further, it has been established that the Amur sleeper Perccottus glenii previously known to occur only in the upper reaches is now widely distributed in the rivers of the Ural basin located in Russia. For both fish species, the variation in values of their meristic features falls within their spectrum of variability. A comparative description of nutrition is also presented. The spectrum of objects consumed by Amur sleeper is wider and their sizes are larger than for topmouth gudgeon. Among the common species of Chironomidae, benthic organisms (Chironomus plumosus, Glyptotendipes gripekoveni) predominate in the diet of Amur sleeper, while for topmouth gudgeon the diet includes organisms localized on aquatic macrophytes (Cricotopus algarum, C. sylvestris, and Tanytarsus gregarius) as well as swimming larvae (Cloeon dipterum) and crawling larvae (Caenis macrura) from the order of Ephemeroptera. The nutritional similarity of Amur sleeper and topmouth gudgeon, as species with similar biotopes, is characterized as relatively low in the Ural River.