The causative agent of furunculosis Aeromonas salmonicida is widely spread around the world and usually affects many cold-water fish (trout), salmon, and less often fish from other families. Currently, there is no scheme for indicating the bacterium of the species A. salmonicida from objects of the external environment, using bacteriophages and accumulation media, which complicates the study of the distribution area of the mentioned microorganism and rapid indication of the pathogen. For this reason, the aim of the study was to develop a scheme for the indication of A. salmonicida bacteria using bacteriophages. To identify field strains of A. salmonicida, we examined 56 samples of water objects in Ulyanovsk and the Ulyanovsk region. Using the environment of accumulation of A. Sl.1 and the differential diagnostic environment A.Sl.2.7 A. salmonicida strains were isolated and typed from 56 samples. We have developed a scheme for the indication of A. salmonicida bacteria based on the modification of the phage titer increase reaction (RSF) using the accumulation medium A.Sl.1. This scheme allows detecting A. salmonicida in the amount of 103m.K./ml within 24 hours. The proposed scheme has the potential to be modified and applied to a whole range of microorganisms, sensitive and specific, allowing to detect bacteria in the substrate in a short time, in the presence of foreign microflora without isolation of pure cultures.