Microbiological Approaches to Reducing the Use of Antibacterial Drugs in Fish Farming as a Tool to Improve Ecology in Aquaculture Systems

The novelty of the work is confirmed by the trends in the search and study of microorganisms with probiotic potential that can have a positive effect on fish health and the sustainability of aquaculture systems, and are aimed at improving environmental friendliness in aquaculture. The aim of the research was a comparative study of the antagonistic activity of symbiotic lactobacilli isolated from the intestinal canal of fish and the antibiotic sensitivity of pathogenic aeromonads. The material for the study was microorganisms isolated from the internal organs of fish species: Russian sturgeon, silver Prussian carp, carp, silver carp and amber trout. The bacteria were studied using bacteriological methods by seeding intestinal contents onto nutrient media and subsequent species identification using the MALDI-TOF MS time-of-flight mass spectrometry method. Pathogenic aeromonads of the species Aeromonas hydrophila, Aeromonas veronii, Aeromonas ichthiosmia, Aeromonas salmonicida were obtained and their sensitivity to antibacterial drugs was determined. The degree of bactericidal action of ciprofloxacin, imipenem and cefaclor was established. Amoxicillin had moderate antimicrobial activity. Aeromonas ichthiosmia culture showed the least sensitivity to antibiotics compared to other aeromonads. Species-specific bacteria of their intestinal contents of silver Prussian carp and amber trout belonging to the species Enterococcus faecium, Pediococcus acidilactici, Lactococcus lactis were obtained. The antagonistic activity of lactobacilli was studied in relation to pathogenic aeromonads. A high degree of bacteriostatic action was expressed in the inhibition of microbial growth of indicator cultures of pathogenic aeromonads. Prospects for the use of species-specific lactobacilli of fish were established as new environmentally friendly probiotic feed additives for an alternative to antibiotics.