Duração do teste de desempenho para avaliação genética de tilápias Oreochromis sp.

Abstract

The effectiveness of a genetic improvement program is measured by its genetic gain. However, the lack of defined methodologies regarding the time needed to evaluate the animals and the choice of the parents of the next generation directly implies an increase in the generation interval, a determining factor in the annual increments. The objective of the study was to define the ideal timing of the tilapia performance test for genetic evaluation through the estimation of genetic parameters. The data set used in the analyzes contained information from 495 animals from 24 half brother and full sibling families that went through a 6 month growth test in a closed recirculation system in the Fisheries Sector of the Federal University of Lavras. During the growth test, monthly weighings were performed at 30, 60, 90, 120 and 150 days. Bicaracter analyzes were carried out involving the different weights along the growth test with the final weight, two to two. The identifiable environmental effects considered in the analyzes were fiberglass containers and genre. Age was used as covariate. The heritabilities, common nesting environment effect, genetic and phenotypic correlations were estimated using Bayesian procedures, by the Gibbs chains, through the MTGSAM computer program. The convergence of the chains was tested by the method of Heidelberger and Welch. The effect of common raising environment had the highest value recorded at the first weighing (0.41) and reduced until the last weighing (0.32). Heritability estimates increased with fish growth reaching the highest value (0.25) at 120 days, remaining at this level for up to 150 days. The genetic correlations between weight at 150 days with the other weighings were relatively high, and reached the highest value (0.87) between the weights at 120 and 150 days. Selecting 10% of the animals with the highest genetic values at the last weighing, the simulated genetic gain will be about 58 grams for the next generation, which corresponds to an increase of almost 12% in the average of the progeny. By simulating the response correlated by the selection process of the 10% of the animals with higher genetic values of the previous weighings, it is observed that the genetic gain reduces as the animals are selected earlier. The selection for weight in tilapia loses efficiency as the process is performed earlier and the selection becomes interesting at 120 days, which would reduce in that study, 30 days in the evaluation period, saving time, resources and still maintaining a good perspective of genetic gain.