Selective breeding for increased body weight in a synthetic breed of Egytian Nile tilapia, Oreochromis niloticus: response to selection and genetic parameters

Selection for harvest weight was performed in a fully pedigreed synthetic line of Nile tilapia (Oreochromis niloticus) in Egypt for two generations. Records were available over three spawning seasons (2002, 2003 and 2004) for weight at the beginning of communal rearing (initial weight), harvest weight and survival rate. The data set consisted of 9,267 progeny records from 214 sires and 323 dams. Phenotypic and genetic parameters, as well as response to selection, were estimated fitting an animal model as well as a sire and dam model to the data. Initial and harvest weight were transformed to log10 for analysis. The heritabilities (s.e.) from the animal model for initial weight, harvest weight and survival were 0.106 (0.0576), 0.144 (0.0598) and 0.120 (0.0346), respectively, whereas the corresponding maternal and common environmental effects, c², were 0.652 (0.0475), 0.384 (0.0496) and 0.015 (0.0214), respectively. The genetic correlations had large standard errors, but they were in a favorable direction, especially between harvest weight and survival [0.458 (0.2035)]. Response to selection was estimated in two different ways: (i) From the difference in average breeding values between generations, and (ii) From the difference in breeding value between the selection and the control lines. Using the former method the responses in harvest weight were 6.64 and 6.96 per cent, comparing the progeny of the 2002 with 2003, and 2003 with 2004 spawnings, respectively, giving a cumulative response of about 14 percent in two generations. With the second method, the difference between the control and selection line in 2004 was 3.82 per cent. The results are discussed in relation to other selection work conducted with tilapia, and the future direction of the genetic improvement program is outlined.