Data on length-weight and length-length relationships, mean condition factor, and gonadosomatic index of and from the Ob River basin, Western Siberia.

Raw data were obtained from 250 specimens of roach and 274 specimens of perch at 15 sampling sites located from North to South Taiga. Fish sampling was performed using gill-nets with 22 and 28 mm mesh. Total and eviscerated weights, total and standard lengths, fish sex, gonad weight and maturity stage were recorded.