The Amur, or Heilong Jiang, is the world's tenth longest river, forming the border between the Russian Far East and Northeastern China. The Amur proper is 2,824 kilometres (1,755 mi) long, and has a drainage basin of 1,855,000 square kilometres (716,000 sq mi). Including its source river Argun, it is 4,440 km (2,760 mi) long. The largest fish species in the Amur is the kaluga, attaining a length as great as 5.6 metres (18 ft). The river basin is home to a variety of large predatory fish such as northern snakehead, Amur pike, taimen, Amur catfish, predatory carp and yellowcheek, as well as the northernmost populations of the Amur softshell turtle and Indian lotus.
It is believed there are at least 123 species of fish from 23 families inhabiting the Amur. The majority are of the Gobioninae subfamily of Cypriniformes, followed in number by Salmonidae. Several of the species are endemic. Pseudaspius and Mesocottus are monotypic genera found only in the Amur and some nearby coastal rivers.
Four species of the Acipenseridae family can be found: the kaluga, Amur sturgeon, Sakhalin sturgeon and sterlet. The Kaluga and Amur sturgeon are endemic. The sterlet was introduced from the Ob in the 1950s.