Abstract <p>The results of the study of the biological indices of the pike-perch (<i>Sander lucioperca</i>) introduced into Lake Sundozero, the Baltic Sea basin, are reported. It is shown that its purpose-oriented introduction attempted for the qualitative improvement of fish fauna composition has been successful. High potentials of pike-perch and favorable environmental conditions have contributed to its naturalization. In biological indices, it is more similar to pike-perch from the parent water body, Lake Syamozero. The successful introduction of pike-perch was determined by similarity in environmental conditions between donor water bodies and the recipient water body, sufficient food supply for the colonizer at all stages of its life cycle, and favorable reproduction conditions. Now, self-settling of pike-perch from Lake Sundozero to Lake Pandozero along the Suna River is recorded.</p>