The scale reading method was used to calculate present and back age ofB. australiscaptured monthly during a 19‐month period at Las Balsas, Rapel Reservoir Chile. Three age groups were determined: group I from 130 to 210 mm T.L., group II from 210 to 250 mm T.L. and group III from 250 to 280 mm T.L. The Von Bertalanffy model and Walford's method were used as a mathematical expression of growth. Growth equations are: