The paper presents the results of selecting methods for establishing the growth rate, generation time and doubling of the biomass of yeast cells Rhodotorula spp., which are part of probiotic feed preparations for aquaculture objects. The identified atypical period of the lag phase was observed on both studied nutrient media (Lundin, YEPD), where instead of an increase in the biomass of the culture, some of the introduced cells died. The results obtained provide the basis for further study and search for new highly productive strains of Rhodotorula spp., selection of technological regimes for obtaining feed preparations based on them, modification and optimization of the composition of the culture medium to increase the growth of yeast biomass.