An accurate estimation of growth is crucial for any fish species that is a target in fishery. We applied a biphasic Lester model for pikeperch (Sander lucioperca) population that is a slow-growing one. In this model, age at maturity divide the growth into immature and matuire phases. Logistic regression models showed that both age and length were significant in males and females when using maturity as a dependent variable, and both of these variables differed between sexes. To estimate how the changes in used age at maturity affect the Lester model parameters, the effects of ages from 10% to 90% probability of maturity were analysed. The gonadosomatic index of males (max. 2%) and females (max. 8.6%) was used to select Lester models that also gave low estimates for the investments in reproduction (g). Low g values were found in the Lester models for ages from 60% to 90% probability of maturity in males, and from 30% to 70% in females.