The determinant includes both indigenous inhabitants of fresh water, as well as passing and semi-passing fish entering fresh water from the seas and oceans for spawning and feeding. To facilitate the use of the determinant, the book gives concepts about the systematic categories and classification of fish, about the main morphological signs and measurements of fish necessary for determination, indexes of Russian and Latin names of fish are made. Color and black and white illustrations will contribute to the definition. The book is intended for biology teachers and students of pedagogical universities.