Genetic changes during mass selection for growth in Nile tilapia, Oreochromis niloticus (L.), assessed by microsatellites
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Two control (C1 or first control generation, and C4 or fourth control generation) and three selected (S1 or first selected generation, S2 or second selected generation, S4 or fourth selected generation) stocks of Chitralada Nile tilapia were analysed for microsatellite variation to determine the effect of size-specific mass selection on genetic variability. Genetic variation based on five microsatellite loci (UNH123, UNH147, UNH172, UNH222 and UNH216) showed a slightly higher allelic diversity in the selected stocks (7.4–10 alleles) than in the control stocks (6.8–8.8 alleles). Apparent reductions in the mean number of alleles and He values were noted in successive generations of both control and selected lines. Significant deviations from Hardy–Weinberg equilibrium because of an excess of homozygotes indicated inbreeding in all control and selected stocks. Although estimated inbreeding levels were not significantly different among selected and control lines based on Welch's t-tests, the increase in the degree of inbreeding within the selected line was higher (107.9%) than the control line (64.2%) after four generations. The implications of these results on the management and conservation of genetic diversity in improved breeds are discussed, while the importance of monitoring and minimizing inbreeding are likewise emphasized.
CitationRomana-Eguia, M. R. R., Ikeda, M., Basiao, Z. U., & Taniguchi, N. (2005). Genetic changes during mass selection for growth in Nile tilapia, Oreochromis niloticus (L.), assessed by microsatellites.
The authors would like to thank Ms. Adelaida L Arago, Messrs. Bienvenido Banaag and Federico Reyes for their technical assistance. The Japan Society for the Promotion of Science (JSPS) and SEAFDEC are gratefully acknowledged for funding this study.
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Selective diversification of aquaculture stocks: A proposal for economically sustainable genetic conservation RW Doyle, NL Shackel, Z Basiao, S Uraiwan, T Matricia & AJ Talbot -
Canadian Journal of Fisheries and Aquatic Sciences, 1991 - NRC Research PressThe genetic diversity of aquaculture stocks can be maintained, and their genetic impact on wild stocks minimized, by breeding programmes that deliberately generate genetic diversity. Current animal breeding practices are likely to reduce the diversity of domestic stocks if they are extended to aquaculture. It is proposed that national breeding programmes for aquaculture should, instead, try to develop numerous breeds specially adapted to local environments and aquaculture systems. An economic model is presented of decision-making by individual farmers who, in choosing which breed to produce, determine the "fitness" of the breeds in a meta-population that includes all breeds. As long as strong genotype-environment interaction for production traits is maintained by artificial selection, the economic self-interest of farmers should ensure the stability of genetic polymorphisms among breeds. Genetic variation would be conserved (in the among-breed component of genetic diversity) but not the primordial distribution of gene and genotype frequencies. Economic benefits to farmers, plus a high return on investment at the national or supra-national level, makes breed diversification an attractive conservation strategy even though it is admittedly a compromise from a purely genetic viewpoint.
magazineArticleDetermining changes in the genetic diversity of selected hatchery stocks through DNA-level polymorphisms analysis provides aquaculturists with a means to monitor inbreeding, control loss of genetic diversity, and achieve sustainable levels of genetic gain in the development of improved stocks. Tests with selected and domesticated tilapia stocks in the Philippines revealed variability between marker system results.
ArticleOpportunities for developing small-scale tilapia industry in the Philippines is hampered by the shortage of good-quality seeds and broodstock. Most small-scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ~ 122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer-based research on tilapia breed improvement using relatively simple artificial selection procedures. One generation of size-specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B-net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ~ 16% for standard length and ~26% for weight comparable with similar studies conducted by other workers.