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Feed efficiency of rainbow trout can be improved through selection: Different genetic potential on alternative diets¹

A. Kause^*,2, D. Tobin, D. F. Houlihan, S. A. M. Martin, E. A. Mäntysaari^*, O. Ritola and K. Ruohonen

^* MTT Agrifood Research Finland, Animal Production Research, Animal Breeding, FIN-31600 Jokioinen, Finland; and School of Biological Sciences, Department of Zoology, University of Aberdeen, Aberdeen, AB24 2TZ, UK; and Finnish Game and Fisheries Research Institute, Tervo Fisheries Research and Aquaculture, FIN-72210 Tervo, Finland; and and Finnish Game and Fisheries Research Institute, Turku Game and Fisheries Research, FIN-20520, Finland

² Corresponding author: Antti.Kause{at}mtt.fi

To assess the genetic potential for selection of increased feed efficiency in rainbow trout (Oncorhynchus mykiss), we estimated the heritabilities and correlations for BW, daily weight gain (DG), and daily feed intake (DFI). Body weight was recorded 5 times, and DG and DFI 3 times during a feeding trial lasting 22 mo. To test the hypothesis that phenotypic and genetic parameters were influenced by a nutritional environment, fish were fed either a modern normal protein diet (NP, 40 to 45% protein and 30 to 33% lipid) or an alternative high protein diet (HP, 50 to 56% protein, 20 to 24% lipid) in a split-family design. Results showed that there were no large differences in heritabilities between the diets. Average heritability for DFI over both diets and different fish ages was low (average h² = 0.10), indicating that modest genetic changes in response to selection can be obtained. Average heritabilities for BW and DG over both diets and different fish ages were 0.28 and 0.33, respectively. The NP diet enabled fish to express a wide range of BW, as shown by the increased coefficients of phenotypic variation for BW. Fish fed the HP diet showed increased phenotypic variation for DFI in > 750-g fish. On the NP diet, genetic correlations of DFI with DG and BW were very strong for 750- to 2,000-g fish. In contrast, on the HP diet, the respective correlations were moderate to low, revealing more genetic potential to change growth and feed intake simultaneously in opposite directions. An analysis of the predicted selection responses showed that selection solely for high DG improved feed efficiency as a correlated genetic response. Simultaneous selection for high DG and reduced DFI, in turn, may increase genetic gain in feed efficiency by a factor of 1.2 compared with selection solely for DG. However, variation for growth and feed intake and the relationships between these traits were different in different nutritional environments, leading to divergent genetic responses on the alternative diets.

Key Words: feed efficiency • feed intake • genotype-by-environment interaction • heritability • quantitative genetics • rainbow trout

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