Bacterial infections are most dangerous for fish and may cause their 100 % death. The most dangerous bacteria are aeromonas, or pathogens of hemorrhagic septicemia or rubella. The Cyprinids are most susceptible to this disease. As a rule, antibiotics, sometimes probiotics are used to fight aeromonosis. Due to the frequent use of antibiotics, fish develop resistance to some of them, thus making the measures to fight bacterial infection completely ineffective. Nowadays phytobiotics are spreading widely in European countries. Phytobiotics are phytogenous or plant-based complexes that do not contain any drugs, so they are simply referred to as feed additives containing biologically active substances that are able to resist bacterial infections, increase appetite, immunity, improve metabolic processes, etc. The following article provides a research on a phytobiotic “Mix-Oil” and its effectiveness against carp aeromonosis. The phytobiotic "Mix-Oil" is a product of a joint Belarusian-Italian production and is based on the essential oils of oregano, cloves and garlic. It was revealed that the phytobiotic "Mix-Oil" does not have acute and chronic toxicity on carps at a dosage of 80 - 600 g / ton of compound feed. Both preventive and therapeutic effects of Mix-Oil as a part of carp compound feed were also established. Based on the results obtained, it was concluded that a dosage of 600 g / ton of compound feed is the optimal dosage of phytobiotic in mixed feed. Since the phytobiotic "Mix-Oil" is a heat-sensitive product, the modes of moisture and heat treatment as well as a type of granulation were selected, in which the phytobiotic retains its activity. The optimum parameter values of the moisture and heat treatment of mixed feed with phytobiotic “Mix-Oil” at a dosage of 600 g/t were determined, without loss of activity of the phytobiotic, such as: the temperature of the loose mixed feed before the press granulator matrix is not exceeding 67° С and the duration of the moisture and heat treatment process is not exceeding 5,8-6 seconds. On the basis of the conducted research, a new treatment-and-prophylactic compound feed “Mix-Feed” was developed, together with technical specifications for it: TS BY 100035627.020-2018 “Granulated Compound Feed for two and three year old carps“ Mix-Feed ”K-111-LP”. It is recommended for feeding carps during spring and autumn within 5 to 10 days to increase the resistance of fish to bacterial infections. Mix-Feed has passed industrial tests and is used by fish farms of the Republic of Belarus.