Estimação de parâmetros genéticos para características morfométricas e de desempenho em tilápias do Nilo utilizando modelos de regressão aleatória

Abstract

The aim of the current study was to estimate genetic parameters for weight gain and body measurements. in Nile tilapia GIFT strain by random regression models. It was tested several orders of Legendre polynomial and models with 1, 3.6 and 9 classes of residual variance. The best fit was defined considering the presence at least one eigenvalues close to zero in each of the random effects, beyond, it was used the ratio test of Maximum Likelihood. For the uni-trait analyses, Legendre polynomial of third order were used to fit effects of permanent environmental and family at all traits, and genetic effect of weight, weight gain, length and width. For genetic effect of height and size head were needed polynomial of fourth order. To gain weight, height and head the best model was the one that considered the residual variance homogeneous for width, heterogeneous variance with 3 age's classes and for weight and length, heterogeneous variance with 9 age's classes. The highest heritability (h2) for weight was 0.34 at 240-311 days of age. For the weight gain was 0.69 at 311 days, 0.2 from 254 days onwards for height, 0.27 at 270 days for head, 0.21 at 270 days for length and wide was 0.54 at 311 days for width. Since the largest heritability were found for weight gain and width at 311 days, selection at these ages, based on these traits would lead to greater genetic gains. Genetic correlations were higher between adjacent ages and, in general, genetic correlations for 300 days and other ages are higher close to 200 days of age, indicating that selections at ages less than 200 days won't lead to gains correlated with the traits at 300 days, except for width which high correlations were obtained between final and initial ages and also the heritability were median in the most of the period, thus, the selection based on the width at any age would lead to satisfactory genetic gain in this trait at the end of the growing season.