Using a collection of modern roach (Rutilus rutilus lacustris) specimens collected from Lake Baikal and with known body sizes, regression equations for estimating the total length of this species are developed. These equations relate dimensions taken on select skeletal elements of the head region to the total body length. The equations are applied to roach skeletal elements recovered from the Ityrkhei archaeological site, which is located on the southern Little Sea of Lake Baikal, in order to reconstruct the sizes of fish harvested here during the Holocene (especially in the period from 9230 to 4970 cal. years BP). Results of the study indicate that the average size of roach taken at the site was around 26.45 cm. Also presented in the paper are previously developed regression formulas for estimating the total lengths of perch (Perca fluviatilis) from Lake Baikal, also constructed using modern specimens with known body dimensions from the lake. Remains of perch were dominant among the fish specimens recovered from the Ityrkhei site. Results suggest that both perch and roach were primarily taken by the inhabitants of the Ityrkhei site through the use of large gauge nets or traps.