An Overview of Progress toward developing and all Plant-based Diet for Rainbow Trout

Feeds for rainbow trout have historically contained high quantities of fish meal and fish oil as cost effective sources of both essential amino acids and fatty acids. Research results from around the world have identified ingredients to replace fish meal and fish oils, but limits still exist in completely removing these ingredients from the diet. The USDA-ARS Trout-Grains Project, officially titled “The integration of nutritional, genetic and physiological approaches to improve production efficiency of rainbow trout (Oncorhynchus mykiss)” was initiated with a primary goal to identify cost effective replacements for fish meal. The project team consists of two fish nutritionists, a fish geneticist, a grain chemist and a plant geneticist. This group of scientists addresses a range of issues, including selection/development of cereal grains with improved nutritional profiles, development of methods to fractionate valuable components of grains, and development of families of trout that are better able to utilize nutrients from plant-based feeds. The nutrition component of the project focuses on evaluation of new and traditional ingredients, nutrient requirements for specific life stages, and identification of nutrients in fish meal not present in plant meals. Finally we are developing a database of nutrient availability from plant-based ingredients that will have potential to supply the nutritional needs of rainbow trout in aquaculture. Some highlights of our research findings have been: 1) Taurine may be conditionally indispensable when only plant-derived protein sources are utilized. 2) Vitamin premix formulations benefit from modification when fish meal is replaced by plant derived ingredients, or when poor quality fish meals are used in extruded trout feeds. 3) Starch amylose/amylopectin ratios in energy feed ingredients will affect carbohydrate and energy digestibility. This article will present the results of laboratory and pilot scale studies of feeding fish meal-free diets to rainbow trout.