Introduction

1. Evaluation of family growth response to fishmeal and plant-based diets in rainbow trout (Oncorhynchus mykiss) L. Pierce1,2, Y. Palti1, J. Silverstein1, R. Barrows3, E. Hallerman2, J. Parsons4 1National Center for Cool and Cold Water Aquaculture USDA/ARS, 11861 Leetown Rd., Kearneysville, West Virginia 2Department of Fisheries and Wildlife Sciences, Virginia Tech, Blacksburg, VA 24061 3USDA-ARS, Hagerman Fish Culture Experiment Station, 3059-F National Fish Hatchery Road, Hagerman, ID 83332 4Troutlodge, Inc., 12000 McCutcheon Road, Sumner, WA 98390 Abstract: Both environmental and economic concerns have led to the development of fish-meal free diets for salmonids. The ability of rainbow trout to efficiently utilize plant-based diets for growth and reproduction, and the genetic variation within populations for these traits, has not been thoroughly examined. In a previous study we used microsatellites to determine the pedigree of the top 1% and bottom 1% of progeny in a commercial growth trial of 20 full-sib families reared in a common environment. Half of the fish from each family were fed a standard fish-meal based diet and the other half were fed a plant-protein (gluten) based diet. The family rankings were similar when either diet was fed, indicating no genotype x diet interaction is present in that commercial trout strain. In the present study growth rate of a pedigreed population from another commercial strain was assessed feeding both plant-based and traditional fish-meal diets. Families (95 full-sib or 47 half-sib) were reared in a common environment and parentage assignment performed on approximately 1000 fish fed each diet. Fish that were fed the control (fish meal/oil) diet were significantly larger then the plant diet fish. Unlike the previous study, a significant genotype x diet effect of 5% was detected and 73% genetic correlation was estimated for growth rate on the two diets. The difference between the two studies was likely caused by the addition of soybean meal and oil to the plant diet used in this study and the experimental design that enabled quantitative assessment. The use of a different strain may have contributed to that difference as well. The genetic variation we identified can be explored to identify and select for genes involved in improved utilization of plant based diets containing soybean meal and oil. Introduction Results • The aquaculture industry has received criticism regarding the volumes of fishmeal and fish oils used in the manufacture of salmonid feeds due to: • Negative environmental impacts (water quality and nutrient loading) • Oceanic forage fish possibly limited • Feed expense • By evaluating family growth response to fishmeal and plant-based diets, we can asses the magnitude of genotype x diet interactions and determine if the fish we are selectively breeding for today, will perform the same on the diets of tomorrow. • Parental Analysis: • PAPA and FAP • 1, 962 individuals ran (PP 988+FM 974) • 34 deleted: genotypes not obtained for ≥2 markers • Comparison: • 29 called differently: • Nine ambiguities were missed by PAPA • Statistical Analysis: • SAS • Fixed effects (Figure 2) shows a significant growth difference and tank effect between the two diets • This data shows larger individual growth on fishmeal than plant-based diets Objectives • Examine growth parameters using a family means approach to compare the performance of progeny from each full-sib and half-sib family fed traditional fish-meal and plant-based diets. • Use DNA marker-based pedigree assignment to accurately allocate progeny to sib groups in a common garden setting of a large-scale broodstock selection program. Table 1. Ingredient composition of diets • Random effects (Table 2) shows a significant genotype x diet interaction • MTDFREML • ~30% heritability of growth was observed • A significant genetic correlation of 73% was seen across diets (Table 3) Methods Figure 2. Diet and tank effects on body weight (g). Bars indicate separate tanks. Fishmeal diet is represented by blue bars and plant diet is represented by yellow bars. Standard error bars are indicated and letters represent significant differences between tanks and diets. Mean average weights in grams are indicated above each diet. • Fish Stocks/Mating Design/Early Rearing/Diet and Feed Formulations • Kamloop Strain from Troutlodge Inc. (Sumner, WA) provided base population • 160 females were mated to 80 males (2 females per 1 male) • Family numbers were reduced at “eyed” stage to 95 full-sib families (9,500 eggs) within a 47 half-sib group (Figure1) and separated into 6 tanks with equal conditions • Diet formulations (Table1) were developed (43% protein/15% fat) and fed until a harvest weight of ~600g was achieved. Conclusions and Future Directions • Parentage Allocation • Although FAP was not designed for this type of study, it did provide additional verification of PAPA’s parental calls. Figure 1. Schematic representation of the 95 x 47 nested mating design, growth trial and parentage determination analysis. • Genotype x diet • Previous studies have shown little evidence for GxD interaction • This study shows significant interaction and lower than expected genetic correlation (rg=0.73) • Could be due to different strain used, addition of soybean meal and oil to plant diet. ♂ ♀ 95 Full-sib Families: (47 half-sib families; ~ 9,500 fish) ♂ Table 2. Family and family x diet effects; highlighted region displays genotype x diet interaction. Table 3. MTDFREML animal model results; highlighted region displays genetic correlation between diets (±SE), values on diagonal are heritabilities. Pooled at eyed stage. Figure 3. Breeding nucleus to select top families for testing and production 100 families breed best test production Growth Trial: Fishmeal diet Plant diet select Genotyping And Parentage Determination: • Future Considerations • Look into “low” correlation; oil source, protein source or genetic source • Identify genes involved in differential utilization of the diets (~27% of the genes involved in feed utilization according to our results) • Selection strategies to considered: • Index selection (multi-trait) • Nucleus broodstock selection (Figure 3) • Alternate generation selection (one for growth on fishmeal and one for growth on plant diet) 1,000 sampled at random 1,000 sampled at random Acknowledgements The authors thank Renee Fincham, Nathan Johnson, Roseanna Long, and Kristy Shewbridge for their technical contributions and guidance. This project is part of the Master thesis research of Lindsey R. Pierce (lpierce@vt.edu). References available upon request. Sampling/Parentage Analysis Random sampling of 1,034 fish were weighed, measured, and fin clipped 1,996 fish total were genotyped using eight microsatellites in a two-multiplex marker system and ran on FAP and PAPA for pedigree assignments