Abstract <p>According to the data of field studies conducted in 2016–2023, the age composition and growth rates of the sun perch <i>Lepomis gibbosus</i> in the basins of two rivers, Seversky Donets and Mius, were analyzed. It is shown that the sun perch from the Seversky Donets River has the largest body length and weight, regardless of age, and the sun perch from the Lugan River has the smallest body weight and length. The former exceeds the latter in all ages by 1.3–1.5 <i>U</i>_cr (<i>p</i> &lt; 0.05) times. The difference in growth between individuals from different water bodies decreases with the age of fish. In the native range, the linear growth of fish is lower, and the sexual maturity of sun perch occurs at the age of 3+ with a life expectancy of up to 10 years; in the basins of the Seversky Donets and Mius rivers, the species reaches sexual maturity at the age of 2+, and their life expectancy is reduced to 6 years.</p>