Abstract
Biological invasions are one of the most powerful negative factors threatening the natural biological diversity and well-being of continental water bodies. In the Aral Sea (Small Aral) basin, it has now been possible to stabilize the catastrophe that arose as a result of the irrational use of water resources. However, the diversity and impact of alien fish species on water ecosystems remains little known. For 10 years, we studied the distribution of one fish species, topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel, 1846) in water bodies of the Aral Basin in the Republic of Kazakhstan. Now, this species is found everywhere in the Syrdarya River itself, floodplain lakes and most tributaries, but is not numerous. Using the example of two small local impoundments, the ratio of the abundance of topmouth gudgeon and other fish species was studied. There was no significant correlation between the presence of topmouth gudgeon and the presence/absence of other fish species. There is also no any significant correlation between the total number of fish (abundance) and topmouth gudgeon abundance, diversity indices and topmouth gudgeon abundance. The findings do not suggest that topmouth gudgeon has a negative impact on other fish species. More likely, this species is able to quickly expand new habitats, but under more stable conditions of water bodies it gives way to other fish species. At high water temperatures, topmouth gudgeon remains the only fish species that feeds on the larvae of blood-sucking Culex and Anopheles mosquitoes.