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. We will use a four-part integrative approach to identify feed efficient trout lines by establishing the phenotypic relationship between residual feed intake and body weight variations using compensatory feeding regimes, tracing stable isotopes in feed, assessing metabolic rate, and correlating gut microbiome with feed efficiency. 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.