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Bentsen H.B.,P.O. Box 5010 As | Gjerde B.,P.O. Box 5010 As | Eknath A.E.,Worldfish Center | de Vera M.S.P.,Worldfish Center | And 8 more authors.
Aquaculture | Year: 2017

Selection for increased body weight at harvest in Nile tilapia (Oreochromis niloticus) was carried out for five generations from 1991 to 1996, as a part of the project Genetic Improvement of Farmed Tilapias (GIFT). The base population for selection was composed of a mixture of various three- and four-way cross individuals descending from four wild African strains and four farmed Asian strains. Methods for single pair mating, separate rearing of full-sib groups and individual tagging and pedigree recording were developed. The parents for a new generation were selected based on a selection index including their own age corrected-body weight at harvest as well as that of their full- and half-sibs. Across generations, a total of 512 males were mated in a nested mating design to 941 females to produce 81,429 tagged progenies. Of those, 56,633 progeny had their body weight recorded at harvest after grow-out testing in a diverse range of farming environments. Estimates of the within generation realized response to selection across farming environments were obtained as the difference between the least squares mean performance of offspring of selected parents and of offspring of parents with average values of the selection index. The average realized response to selection per generation was 13.6% (range 9.0 to 20.1%), resulting in an accumulated response over five generations of 88% relative to the base population. A genetic trend analysis based on BLUP breeding values estimated across generations after the termination of the project suggested an accumulated response of 67%. The genetic composition of the synthetic population also changed during selection. The proportion of ancestors from three of the wild African founder strains increased from 59.7 to 76.3%. The accumulated coefficient of inbreeding was 7.1%. After the termination of the GIFT project, selection was continued in the GIFT population. The population has also been used as a genetic source in a number of similar public and private selection programs. A status review of the presently recorded dissemination of the genetic material and methodology is presented. Statement of relevance The GIFT project showed that five generations of repeated selection based on testing of individually tagged and pedigreed individuals from a synthetic farmed population of Nile tilapia gradually increased the body weight at harvest. The total increase was 67–88%. Reports from several descending populations shows that the selection response has continued during > 10–15 additional generations. © 2016 Elsevier B.V.

Bentsen H.B.,Nofima | Gjerde B.,Nofima | Nguyen N.H.,Worldfish Center | Rye M.,Nofima | And 14 more authors.
Aquaculture | Year: 2012

Phenotypic and genetic parameters for harvest body weight were estimated within and across multiple test environments and five consecutive generations of the synthetic GIFT population. Of a total of about 62,000 individually tagged fish, 43,066 individuals from 461 sires and 815 dams across generations had body weights recorded in two to eight different test environments per generation from 1991 to 1996. The test environments included earthen ponds (fertilized with inorganic fertilizer, organic manure, or on-farm agricultural residues), cage culture, rice-fish, and ponds at test stations located in different agro-climatic regions. Heritability estimates for harvest body weight within test environments and generation were on average h2=0.31 (range 0.06-0.68) and the estimates for effects common to full sibs other than additive genetic effects c2=0.09 (range 0.04-0.16). The estimates tended to be higher in cage test environments. After adjusting for heterogeneous variances of harvest body weight across generations, test environments and sexes, the estimates across test environments within generations were on average h2=0.23 and c2=0.03 over the five generations, while the estimate across all test environments and generations was h2=0.16±0.02 and c2=0.10±0.01. The genetic correlations (rg) between harvest body weights of sibs in different test environments were in general high (0.53-0.99, mean 0.89) for all environments except for intensive cage culture, implying minor genotype by environment (G×E) interactions. The genetic correlations involving the intensive cage culture environment were lower (0.08-0.43) and not significantly different from zero, suggesting that G×E interactions may occur if test environments differ widely. It is proposed that this G×E interaction may involve effects of sexual maturation on growth in pond environments. The overall heritability for body weight at harvest of females (0.20±0.02) was not significantly different from that of males (0.16±0.02). However, these estimates were lower in ponds than in cages, in particular for male body weight. Estimates of genetic correlations between harvest body weight of sib males and females also suggested a moderate sex by genotype interaction in ponds (rg=0.78±0.04) that did not occur in cages (rg=0.97±0.04). These results are consistent with the realization that the GIFT population responds well to selection for increased body weight at harvest across a wide range of pond farm environments (including rice-fish culture) without the need to develop environment specific selection lines. The benefits of specialized selection for intensive cage farming systems should be investigated further. © 2012.

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