Semi-passable fishes - ecological group of fishes that spend most of their life (feeding) in brackish waters of river mouths, sponges (Yenisei, Ob). For spawning rise low in the rivers (bream, carp, pikeperch, etc.), sometimes far from the mouth (muksun, omul, nelma). After spawning, the producers and their young roll out of the rivers to the places of permanent habitat.

A biological group of fishes occupying an intermediate position between resident and passage fishes. Semi-passable fish feed in brackish water at the mouths of seas or in brackish seas-lakes (e.g., Caspian Sea, Aral Sea); for reproduction, they enter the lower reaches of rivers, but usually do not go high upstream. Spawning in fresh water. From the passage fish differ in that they do not live in water with ocean salinity and usually do not go far out to sea. Semi-passable fish include some whitefish, roach, bream and others. Many semipassable fish have commercial importance.