Current Status of Fish Communities in the Danube

Abstract

The Danube is a river with the highest fish species richness (102 species ever reported) in Europe. Nevertheless, it is also a river that faces various human pressures with serious negative impacts on its ecosystems, including fish communities. In this chapter, data from both the Joint Danube Survey 2 (2007) and the Gabčíkovo Hydroelectric Scheme Monitoring (1991–2011) are reanalysed briefly (data from JDS3-2013 are not included). A total of 69 species of fishes were recorded within the recent surveys of the Danube, a number that still suggest a high diversity of the Danubian fish community. However, as many as 12 of these species were not native in the Danube, at least not in its whole course, and a total of 18 non-native species have been ever recorded in the Danube. Concerning native species, cyprinids, especially bleak, highly predominated along the whole course of the Danube, though invasive species, such as gobies in the Upper and Middle Danube and gibel in the Lower Danube, were found to be extremely abundant. Biological invasions not only indicate deterioration of environments but also may result in an overall decline in biodiversity. Therefore, a predictive risk assessments and management strategies for introductions and invasions of non-native fishes should be developed for the Danube and applied subsequently at an international level. Human impacts on fish communities of the Danube are also briefly illustrated, with the Gabčíkovo Hydroelectric Scheme used as an example.