Looks upon the changes in the structure ichtyofauna of the pool of Nizhniy Obi that have occurred in the last 20 years. Shows the main concepts in the production of "sig" fish in the rivers of polar and near polar Urals. Distinguishes an ongoing decline in the number of “peliad” generation, “sig-pizhiyana” and “chira” as well as the lack in the near years is a pre-requisite for the occurrence of the next generations. It is noted that the current level of pollution of the Ural water flows of the Obi, the catch of the Obi and its lip could not account for the changes in the amount of the fish population. The main reason for the decline in the "sig" fish is trade. Therefore, we can concur that the development of the program "Urals industrial – Urals Polar" will have negative affects on the populations of fish in the Obi River, because the potential road will run through the main regions where these fish’s habitats lie.