Correlated Genetic Changes in Commercial Traits to Selection for High Growth in Red Tilapia ( <i>Oreochromis</i> spp.)

The present study examined correlated responses in commercial traits of economic importance resulting from selection for high growth over eight years in a population of red tilapia (Oreochromis spp.). During this period, data on total length, body colour and survival were recorded for 75,950 individual fish, which were progeny of 1203 dams and 608 sires. Our restricted maximum likelihood-mixed model analysis showed that selection for increased body weight produced concomitant positive changes in animal length by 3.1%. A correlated increase of 4.9% per generation was also observed for the survival rate in this population. Body hue colour, a trait of commercial interest, displayed a slight increase of 1.8% per generation. The substantial improvement in total length is consistent with the high genetic correlation (r_g) between body weight and length (r_g = 0.84). Body weight was weakly but significantly correlated genetically with the survival rate during the grow-out period from stocking to harvest. However, the genetic correlations between weight (or length) and body hue colour were not significant. Furthermore, there were substantial heritable genetic variations in these traits, with heritability estimates ranging from 0.12 to 0.36. Maternal and common full-sib effects accounted for 2.5%-17% of the total phenotypic variation. It is concluded that selection for increased body weight resulted in desirable correlated responses in complex quantitative traits of red tilapia, and these genetic characters will continue to respond to selection, given the substantial genetic variation in this red tilapia population.