Technical Abstract: Although the search for alternatives to fish meal in aquafeeds has been active for the last 30 years, efforts in the last decade have been intensified on a world wide scale. Multiple factors are driving these efforts and include regulatory concerns on the environmental effects of nutrient release, the perceived sustainability of feeding fish meal to fish, and the rapidly rising cost of fish meal. The search for alternatives to fish meal has led in many directions, but plant-derived ingredients and single cell proteins such as yeasts, bacteria, and micro-algae seem to offer the most promising possibilities. Animal by-products often have phosphorus levels that severely limit dietary inclusion levels due to environmental regulations. In addition, recent regulations in the U.S. concerning the use of mammalian products by the Food and Drug Administration further discourage the use of mammalian by-products in aquafeeds. Grains and oil seeds are low phosphorus, sustainable, readily available nutrient sources and will probably be major ingredients in trout feeds of the future. Commercial trout feeds today contain much higher levels of plant ingredients and lower levels of fish meal than just 3-4 years ago, but continued progress in reducing dietary fish-meal is limited by the characteristics of available ingredients. Further processing of plant-based ingredients before feed manufacturing, called pre-process modification, can increase inclusion limits. Plant-based ingredients in future salmonid diets will have improved nutrient profiles, relative to traditional ingredients, with reduced fiber and anti-nutrient contents. Future ingredients will also be improved by starting the modification process with superior cultivars of grains and oilseeds. The nutritional value, along with the burden of anti-nutritional and non-nutritional factors and most importantly the cost of the improved characteristics, will ultimately determine their utilization in commercial salmonid diets.