The microbiocenosis of the intestines of fish is represented by the abdominal and parietal microflora, which has complex functional connections with each other and with the intestinal wall. The purpose of the study was to identify the features of the biodiversity of the intestinal intestinal microflora of rainbow trout grown in fish farms in Karelia. The study of intestinal intestinal microflora of rainbow trout was carried out on the basis of fish farms of the Republic of Kazakhstan, geographically located in the water area of 4 reservoirs, characterized by a complex of hydrological, hydrochemical and hydrobiological characteristics. These are the Kondopoga Bay of Lake Onega, the Rautalakhti Bay of Lake Ladoga, Kroshnozero and Lake Nasonovskoye. For statistical processing of the data obtained based on the results of a comparative analysis of the intestinal intestinal microflora of the studied groups of rainbow trout, the compilation of a variation series, the calculation of the average value of the studied trait and the average standard error were used. The object of the study to study the composition of intestinal intestinal microflora was the rainbow trout Parasalmo mykiss (Walbaum, 1792) of the Rofor breed. Microbiological analysis has shown that the qualitative and quantitative variability of the gut microbiome differs depending on the trout growing environment. 14 functional groups of bacteria were identified: cellulolytics, bacilli, lactobacilli, bifidobacteria, selenomonas, actinobacteria, enterobacteria, fusobacteria, peptococci, staphylococci, campylobacteria, pathogenic clostridia, pasteurella and pseudomonas. The proportion of cellulolytics (Eubacteriaceae, Clostridiaceae, Lachnospiraceae, Ruminococcaceae, Bacteroidetes, etc.) varied from 49.1 to 55.3%; bacilli – from 0.9 to 8.7%, lactobacilli – from 5.0 to 13.7%.