Growth curves by Gompertz nonlinear regression model for male and female Nile tilapias from different genetic groups

Abstract

The aim of this study was to estimate the growth curve of Nile tilapia from different genetic groups and to examine possible differences in the growth between sexes using the Gompertz model. The Gompertz function was tested with eight different models: the first model without restriction in the parametric space and the other models at were restricted one, two or three parameters. The fish were classified into three genetic groups: Superior, Medium, and Inferior according to their estimated breeding value for average daily weight gain. Growth of genetic groups indicated that male and female fish showed similar growth during the first 165 days of age, probably due to the onset of reproduction. The estimated asymptotic values for body weight of males from Medium and Inferior group were 69% and 49% smaller than the asymptotic weight of Superior males, respectively, confirming the impact of genetic differences on the phenotypic expression in fish, in which animals with high estimated breeding value (Superior group) had a higher growth rate than others. The Gompertz model was useful to describe growth in Nile tilapias. The estimates of asymptotic weight for females were smaller than of males. Fish from the Superior genetic group presented higher growth rate, asymptotic weight than other groups in both sexes.