This article analyzes the biodiversity of the ichthyofauna of Lake Sarykamysh located in the Fergana Valley. The fish species composition was formed as a result of interaction with the Syrdarya River, since the lake takes its water from this river, and during a flood, water from rivers flow into lakes. During the study, 20 species of fish belonging to 6 orders and 11 families were identified in Lake Sarykamysh. Of these, 8 species are invasive, 5 are acclimatized and the remaining 7 species are local fish. It was found that two-thirds of the ichthyofauna of Lake Sarykamysh consists of introduced fish species. A linear logarithmic indicator between the mass and body length of fish, linear growth over the years of life of fish in Lake Sarykamysh in the basin of the upper reaches of the Syrdarya River were determined. The lake is home to typical predators such as Esox lucius, Sander lucioperca, Silurus glanis, Channa argus and Opsariichthys bidens, and in fairly high numbers. This means that the lake is a favorable habitat especially for predatory fish. The linear growth of fish over the years of life is of interest not only from an economic, but also from a biological point of view. This indicator to a certain extent characterizes the living conditions of fish. A particularly important indicator of fish growth is the growth rate over the years of life, since fish, unlike other vertebrates, grow throughout their lives, that is, their linear growth occurs continuously. For example, the Alburnus chalcoides sample consisted of two and three year old individuals. At the same time, the growth rate was the highest in the first and second years of life; in the third year of life, the growth rate decreased sharply. Alburnus taeniatus has rapid growth only in the first year of life and a sharp slowdown in the second year of life. The slowdown in fish growth is explained by their reaching sexual maturity.