Since the purpose of breeding programs is to manipulate the frequency of genes involved in the expression of a characteristic it is important to understand the associated changes that occur in other characters due to the selection and to what extent they are transmitted to the progeny. The present study reports for the first time in yamu (Brycon amazonicus), an estimation of genetic parameters for the variables weight and height at 25, 40 and 55 days post-hatch. A total of 900 progenies of six couples were analyzed using the statistical package SAS 9.3 (SAS Institute). A general linear model including the fixed effects of environmental factors and genetic factors as random effects were assumed. To estimate the components of variance and covariance the VARCOMP procedure was used under the restricted maximum likelihood method (REML). The average weight estimated heritability was 0.37 ± 0.22 and 0.58 ± 0.30 for size. Genetic and phenotypic correlation between weight and height was positive on average 0.39 ± 0.19 and 0.55 ± 0.14, respectively. The correlation for height and weight was positive and increasing, depending on age. These results suggest that direct selection by size at around 55 days posthatch, will also increase the weight indirectly. This study highlights the genetic potential to improve yamu industry, once progress is made in the areas of morpho-physiology, nutrition, reproduction and health of the species.