Aquaculture provides sustainable production of food fish with high protein/low-saturated fat to satisfy increasing demand. Globally, efficient and environmentally sustainable aquaculture production systems are urgently required. Over two decades of selective breeding, our research resulted in development of a rainbow trout strain that grows as well on an all-plant protein diet as on a fishmeal-based diet, and grows much faster than non-selected trout. Feed accounts for over 60% of the cost of aquaculture production. To date, no commercial breeding programs have selected for improved feed utilization efficiency in fish, mainly because of the difficulty in accurately measuring individual feed intake of fish reared in groups. Therefore, for this project, we will develop an indirect benchmark to use in selecting trout for improved feed utilization efficiency of soy protein protein-based diets, with the long-term goal of reducing the cost of producing commercial trout. Results of each objective will be compared and validated for feed efficient trout lines. Currently, major commercial trout producers, providing a pipeline for transferring our findings directly to stakeholders, are using our selected trout lines. Overall, successful selection for improve feed efficiency will have a broad application to commercial fish selective breeding programs, leading to increased profitability for US farmers.

The overall goal of the proposed project is to develop alternative approaches to select the families of rainbow trout to enhance the efficiency of soybean based diets utilization. For this project, we will develop an indirect benchmark for use in selectively improved families of rainbow trout for feed efficiency of soy protein-based diets (SBMD) utilization, with the long-term goal of reducing the cost of trout production in the aquaculture industry. During this three-year period, we will address this goal with the following objectives:
Objective 1: to develop an indirect set of benchmarks to be used in selection of rainbow trout to enhance the efficiency of growth and utilization of plant protein-based diets.
Objective 2: to identify the variation in trout families for improved feed efficiency using stable isotopes in feed.
Objective 3: to quantify the genetic potential gain of fish via calculating heritability towards the utilization of SBMD in terms of growth performance and feed efficiency.

• Indirect criteria to enhance the utilization of soybean based feed efficiency in fish. Acceptance of fish breeders, feed manufacturer and nutritionists, and aquaculture producers to utilize the high soy meal in aquaculture feeds.
• Results of this research will be presented at ‘Aquaculture America 2025, and 2026; Idaho aquaculture association meeting in 2025 and 2026, and trout farmers conference 2025 and 2026 where fish nutritionists, fish feed manufacturers, feed ingredient suppliers and aquaculture producers are in attendance.
• Manuscripts will be submitted for publication in peer-reviewed journals.
• Technical Bulletin
• Quarterly Progress update
• Final Report

Updated August 15, 2024:
Objectives 1 and 2 have been completed. Two studies to establish an indirect set of benchmarks to be used in selection of rainbow trout to enhance the efficiency of growth and utilization of plant protein-based diets were performed. The first was based on the incorporation of isotopically labeled amino acids by trout from the feed as an indirect measure of protein efficiency. The second was a fed-fast study to measure residual feed intake in trout. For both studies, the fish were statistically separated into performance quartiles, with high and low performing fish selected for breeding this fall. The offspring will be evaluated in the spring of 2025 for performance on high soy feeds and used to estimate the potential genetic gain towards the utilization of soybean meal-based diets (SBMD) in terms of growth performance and feed efficiency (Objective 3).

Updated December 3, 2024:
During the fall 2024 spawning season, twelve crosses were generated from the families categorized for growth and isotope retention in the SAA study. These crosses consisted of 4 high x high crosses (retention/growth), 4 low x low crosses, 2 average by average crosses and 2 high x low crosses utilizing alternative high and low males and females. Eggs are currently in the eye-up stage and will be hatched, then reared to approximately 20g in the spring for use in a growth study to evaluate the success of the selection process and heritability of the performance traits.

Updated March 28, 2025:
Objectives 1 and 2 have been completed. Two studies to establish an indirect set of benchmarks to be used in selection of rainbow trout to enhance the efficiency of growth and utilization of plant protein-based diets were performed. The first was based on the incorporation of isotopically labeled amino acids by trout from the feed as an indirect measure of protein efficiency. The second was a fed-fast study to measure residual feed intake in trout. For both studies, the fish were statistically separated into performance quartiles, with high and low performing fish selected for breeding this fall. The offspring will be evaluated in the spring of 2025 for performance on high soy feeds and used to estimate the potential genetic gain towards the utilization of soybean meal-based diets (SBMD) in terms of growth performance and feed efficiency (Objective 3).

During the fall 2024 spawning season, twelve crosses were generated from the families categorized for growth and isotope retention in the SAA study. These crosses consisted of 4 high x high crosses (retention/growth), 4 low x low crosses, 2 average by average crosses and 2 high x low crosses utilizing alternative high and low males and females. Eggs were hatched and reared for the feeding trial.

Currently, we have families of trout representing all crosses. They are now approximately 10 g body weight. The first week of April they will be stocked into tanks for the final feeding trial, where the will be feed a high-soy diet with growth and feed efficiency evaluated over 12 weeks. These results will be used to complete Objective 3, quantifying the genetic potential gain of fish via calculating heritability towards the utilization of SBMD in terms of growth performance and feed efficiency.

Trout industry in the United States is a significant consumer of soybeans. The outcomes will contribute to start the genetic improvement program by producing brood stock of rainbow trout with the traits of best soybean based diets utilization efficiency, which is good news for the aquaculture industry including the fish farmers, and feed industry especially the soybean producer. This increase in soybean usage would positively impact the soybean farmers and the overall economy.