Danube
The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world. Ordered from the source to the mouth they are:
The Danube is navigable by ocean ships from the Black Sea to Brăila in Romania and by river ships to Kelheim, Bavaria, Germany; smaller craft can navigate further upstream to Ulm, Württemberg, Germany. About 60 of its tributaries are also navigable.
Danube bleak
The Danube bleak is an elongate slim fish which can reach but a more normal size is 15 to 30 centimetres (6 to 12 in). There are 57 to 70 scales along the lateral line. The abdomen is compressed into a keel and the posterior end of this has no scales. The dorsal fin has eight to nine branched rays while the anal fin has fifteen to nineteen. This fish is morphologically quite variable which may be due to local adaptations to various habitats but is more likely to be due to several species being involved.