12 SEPTEMBER 2012 destroy improvements obtained in the previous generations. DNA tagging should be used to keep track of relationships and control inbreeding. Still, individual selection is limited to those traits that can be measured. Family-based breeding programs have the advantage that economically important traits, such as product quality and disease resistance, can be selected for based on information from siblings of breeding candidates. Adding genomic information to these schemes increases accuracy. Controlled single-pair mating between unrelated individuals should be practiced in individual selection and family-based breeding programs. The number of progeny per mating should be standardized. In family-based breeding programs, it is advantageous to rear families separately until tagging and then use communal rearing thereafter. This means that infrastructure must be established to produce a high number of families (at least 100) per generation. With genetic markers for identification, communal rearing is possible, reducing the need for infrastructure. However, this approach may result in a reduced number of families and large variation in family size, thus introducing genotyping costs. For all approaches, to keep the generation interval as short as possible, estimation of breeding values should take place as soon as data is available. Consequences of Using Selective Breeding in Aquaculture Assuming a genetic gain in growth rate of 12.5 percent per generation, estimated global aquaculture production increases with greater use of selective breeding (Table 2). The impressive effect of selection is that genetic gain is cumulative over generations. Global production would be doubled by 2020, representing 5-6 generations of selection, if all of it was based on genetically improved stocks (Table 2). Breeding programs for Nile tilapia and Atlantic salmon have already shown that this is possible. In addition, commercial Atlantic salmon aquaculture is an example where nearly all production is currently based on improved stocks (Gjedrem 2004). It is not realistic to expect that all of global aquaculture production will be based on improved stocks because of the high number of species in aquaculture, with a resulting need for a high number of breeding programs. According to FAO (2007) there are 241 species used in global aquaculture and, among them, 124 species with production above 1000 t. From a resource use efficiency point of view, there is much to be gained by applying selective breeding. Doubling growth rate with 5-6 generations of selection reduces the production time by almost 50 percent. Food production will increase and there will be more efficient utilization of production facilities (i.e., ponds and cages), labor, water and feed (Thodesen et al. 1999), making aquaculture an even more cost-efficient and sustainable proposition. Investments in efficient breeding programs are cost effective. For fish, the estimated benefit-cost ratios for breeding programs vary from 8-1 to 60-1 (Gjerde et al. 2007, Gjedrem 1997, Ponzoni et al. 2007, Ponzoni et al. 2008, Robinson et al. 2010). The economic value of better feed efficiency in Atlantic salmon after six generations of selection is estimated to be US$ 0.50 per kg fish produced (Gjerde et al. 2007). Aquaculture for the Future The paramount objective for aquaculture in the future is the sustainable production of animal protein. This can only be obtained if we use animals that have been selectively bred for improved performance in aquaculture production environments, not by using wild animals that do not thrive under these conditions. By increasing growth rate, more foodfish will be produced in a shorter time, production will become more costefficient, feed will be more efficiently converted into animal protein (Thodesen et al. 1999), and mortality will be reduced because less time will be required to reach market size. The potential to improve disease resistance is well documented (Leeds et al. 2010, Sahoo et al. 2011, Storset et al. 2007). Selective breeding is crucial for cost-efficient production, animal welfare, and minimizing the impact of aquaculture on wild populations. These aims can be obtained only by efficient breeding programs. It should no longer be acceptable that 90 percent of aquaculture production is based on wild and genetically unimproved animals. The status quo is an inefficient way of using natural resources, particularly feed-related resources, and is a misuse of valuable land, water, and labor. Selective breeding increases the rate of domestication and improves animal welfare (Doyle 1983) and results in more predictable and reliable production. We should learn from terrestrial farm animal and plant agro-industries that have been using selectively bred stock for many decades. The time has come for aquaculture producers and other stakeholders to cooperate with government authorities and institutions to plan and start breeding programs for each of the most important species in aquaculture. There is a foundation of available literature, knowledge and experience on which to build. Notes 1 Nofima, PO Box 210, 1431 Ås, Norway References Bentsen, H.B., A.E. Eknath, M. Rye, J. Thodesen and B. Gjerde. 2003. Genetic improvement of farmed tilapias. Response to selection for growth performance in the GIFT project. International Association for Genetics in Aquaculture VIII 33(1): 9-15 November, Puerto Varas, Chile. Chopin, T. 2011. Progression of the Integrated Multi-Trophic Aquaculture (IMTA) concept and upscaling of IMTA systems towards commercialization. Aquaculture Europe 36(4):5-12. Doyle, R.W. 1983. An approach to the quantitative analysis of domestication selection in aquaculture. Aquaculture 33:167-185. Eknath, A.E., M.M.Tayamen, M.S. Palada-de Vera, J.C.Danting, R.A. Reyes, E.E. Dinosio, J.B. Capili, H.L. Bolivar, T.A. Abella, A.V. Circa, H.B. Bentsen, B. Gjerde, T. Gjedrem and R.S.V. Pullin. 1993. Genetic improvement of farmed tilapia: The growth performance of eight strains of Oreochromis niloticus tested in different farm environments. Aquaculture 111:171-188. FAO (Food and Agriculture Organization of the United Nations). 2007. FAO yearbook. Fishery statistics, 2005 100/2, FAO, Rome, Italy.
RkJQdWJsaXNoZXIy MjExNDY=