Providing valuable fish species in aquaculture with high-quality feed is the main factor in reducing production costs and increasing the economic efficiency of fish farms. The costs associated with feed are the most expensive component of fish production. The main task of commercial trout farming is the cultivation of fish in the shortest possible time and with minimal costs. This paper investigates the effect of probiotic supplements based on lactic acid bacteria Lacticaseibacillus paracasei Wf-2, Limosilactobacillus pontis Wf-6, Lacticaseibacillus casei Wf-10, and Lacticaseibacillus paracasei Wf-20 and propionic acid bacteria Propionibacterium freudenreichii P-8 on the growth rates of young rainbow trout in aquaculture. The values of the indicators of cheap trout feed with the introduced probiotic supplement differed slightly, and their properties were not inferior to those of expensive feed. A significant reduction in the content of biogenic substances in the variant with a probiotic supplement was shown. The results of the study indicate the high efficiency and prospects of the use of probiotic preparations in the fattening of young trout in aquaculture.