Typical aquaculture diets contain a large portion of fishmeal. Unfortunately, the source of fishmeal mostly comes from wild-catch fisheries. With a growing human population, the supply of these fisheries is unable to keep up with the growing demand and has led to increased fishmeal costs. As an alternative, other protein sources have been posited such as yeast. This study sought to replace portions of dietary fishmeal with yeast fed to rainbow trout. The microbiome is a vital component in overall fish health, so the microbiome community was investigated following dietary treatment with increasing levels of yeast.