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Previous issue date: 2017 === Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) === Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (Capes) === Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG) === Esta pesquisa foi realizada com o objetivo de avaliar o efeito da intera??o gen?tipo x n?veis de
lisina digest?vel das dietas sobre caracter?sticas morfom?tricas e de desempenho de til?pias do
Nilo, variedade GIFT, em fase de crescimento. O experimento foi constitu?do de duas fases,
sendo que na primeira as til?pias foram alimentadas dos 90 aos 150 dias de idade com dietas
contendo percentuais de lisina iguais a 1,43, 1,53, 1,63, 1,73 e 1,83 e na segunda fase, dos 151
aos 255 dias, os percentuais de lisina das dietas foram iguais a 1,28, 1,38, 1,48, 1,58 e 1,68.
As til?pias foram pesadas dos 90 aos 255 dias de idade com intervalos de aproximadamente
30 dias, foram calculados o ganho de peso total e o ganho de peso di?rio e, posteriormente, as
idades foram ajustadas para 90 e 150 dias na primeira fase, e 185, 220 e 255 dias na segunda
fase. As medidas de altura, largura, comprimento de cabe?a, comprimento padr?o e
comprimento total das til?pias foram coletadas aos 150 dias de idade. A partir desses dados,
foram calculadas as rela??es cabe?a/comprimento padr?o, comprimento padr?o/comprimento
total e largura/altura. Modelos de regress?o aleat?ria, por meio do modelo animal uni
caracter?stica, foram utilizados para avaliar a sensibilidades dos valores gen?ticos aos n?veis
de lisina digest?vel das dietas, plotando-se as normas de rea??o de 25 peixes amostrados
aleatoriamente para as diferentes caracter?sticas para demonstrar o padr?o de comportamento
dos valores gen?ticos das caracter?sticas ao longo do gradiente ambiental. Foram testados
modelos com homogeneidade (1 classe) e heterogeneidade de vari?ncia residual (2, 3 e 4
classes). Modelos com heterogeneidade de vari?ncia residual foram mais adequados para
avalia??o gen?tica da maioria das caracter?sticas das til?pias na primeira fase e modelos com
homogeneidade de vari?ncia residual para a maioria das caracter?sticas de desempenho das
til?pias avaliadas na segunda fase. Os valores gen?ticos das til?pias, em ambas as fases,
variaram entre os n?veis de lisina estudados para a maioria das caracter?sticas, indicando a
presen?a de intera??o gen?tipo x ambiente. No geral, as herdabilidades e vari?ncias gen?ticas
aditivas variaram de baixas a altas magnitudes. As correla??es de Spearman, assim como as
normas de rea??o, indicaram reordenamento dos valores gen?ticos ao longo do gradiente
ambiental, sugerindo a presen?a de intera??o gen?tipo x ambiente. A sele??o para
desempenho e medidas morfom?tricas de til?pias GIFT deve ser realizada no n?vel de lisina
da dieta com a qual as til?pias ser?o alimentadas. === Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Zootecnia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. === This research was carried out with the objective of evaluating the effect of genotype x levels
of digestible lysine of the diets on morphometric and performance characteristics of Nile
tilapia, GIFT variety, in the growing phase. The experiment consisted of two phases, and in
the first the tilapia were fed from 90 to 150 days of age diets containing lysine percentages
equal to 1.43, 1.53, 1.63, 1.73 and 1.83. In the second phase, from 151 to 255 days, the lysine
percentages of the diets were 1.28, 1.38, 1.48, 1.58 and 1.68. Tilapia were weighed from 90 to
255 days of age at intervals of approximately 30 days. Total weight gain and daily weight
gain were calculated and, subsequently, were adjusted for 90 and 150 days in the first phase,
and 185 , 220 and 255 days in the second phase. The measurements of height, width, head
length, standard length and total length of tilapias were collected at 150 days of age. From
these data, the head / standard length ratios, standard length / total length and width / height
ratios were calculated. Single trait random regression modes were used in the analyses and the
reaction norm plots of 25 randomly sampled fishes were used to demonstrate the sensitivity of
breeding values to dietary digestible lysine level. Models with homogeneity (1 class) and
heterogeneity of residual variance (2, 3 and 4 classes) were tested. Models considering
heterogeneity of residual variance were more adequate for genetic evaluation of most of the
characteristics of tilapia in the first phase and models considering homogeneity of residual
variance for most of the performance characteristics of tilapia evaluated in the second phase.
The breeding values of tilapia, in both phases, varied among the lysine levels studied for most
of the traits, indicating the presence of genotype x environment interaction. In general,
heritabilities and additive genetic variances varied from low to high magnitude. Spearman
correlations, as well as the reaction norms, suggested rearrangement of breeding values along
the environmental gradient, again indicating the presence of genotype x environment
interaction. The selection for performance and morphometric traits of tilapia GIFT strain
should be performed at the lysine level of the diet with which the tilapia will be fed.
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