Family growth response to fishmeal and plant-based diets shows genotype × diet interaction in rainbow trout ( Oncorhynchus mykiss)

The ability of rainbow trout to efficiently utilize plant-based diets for growth and the genetic variation for that trait have not been thoroughly examined. In this study, growth of a pedigreed population from the commercial Kamloop strain was assessed while feeding both plant-based and traditional fishmeal-based diets from initiation of feeding to termination of the growth trial at an average body weight of 600 g. Both fish oil (5.00%) and soybean oil (8.43%) were included in the plant-based diet, and only fish oil was used in the fishmeal diet (10.10%). Ninety-five (92 informative) full-sib families nested within 47 (46 informative) half-sib families were reared in a common environment. Parentage assignment was performed on approximately 1000 fish fed each diet using eight microsatellite markers chosen for non-duplication, a minimum of five alleles with no known null alleles, at least 50% heterozygosity, and unambiguous scoring. Progeny were assigned to parental pairs via two allocation programs, PAPA and FAP, to increase accuracy and to test efficiency. The fish fed the fishmeal/oil diet were approximately 8% larger than the fish fed the plant-based diet ( P < 0.05). A significant genotype × diet effect was detected. The variance component for this effect accounted for 5% of the sum of the variance components for all the random effects. The genetic correlation for growth on the two diets was 0.73 ± 0.13, with a heritability of 0.31 ± 0.07 on the plant diet and 0.32 ± 0.07 on the fishmeal diet. We conclude that substantial genetic variation for utilizing plant-based diets containing soybean meal and oil exists in this widely used commercial rainbow trout strain.