The aim of this study was to evaluate the growth curve of selectively bred and non-selectively bred tambaqui (Colossoma macropomum). The experiment involved 388 fish (weight: 65.38 ± 20.00 g; age: 217 days), consisting of 252 fish from seven selectively bred families (18 fish per family) and 18 non-selectively bred fish (control group). Groups were placed in two 800-m² tanks. Biometric measurements were taken on nine occasions at 30-day intervals, for a period of 254 days. Weight and morphometric traits were evaluated. To describe the tambaqui growth behavior, we adopted the Gompertz nonlinear regression model. Greater growth (p < 0.05) was observed in selectively bred families compared with control group. Four families stood out with higher (p < 0.05) asymptotic values for weight (F1: 2448.7 g; F7: 2284.7 g; F5 2180.1 g; F4: 2080.5 g; and control: 1808.4 g) and other morphometric traits. None of the selectively bred families (except F5) had a higher growth rate and age at inflection point than the fish from control group. In conclusion, selectively bred and non-selectively bred fish present distinct growth curves, but some families have greatly superior growth.