Accumulation of opportunistic pathogenic bacteria in the aquatic environment may lead to the changes in the structure of the surface cover microbiocenosis as well as the fi sh intestinal tract. In its turn, it causes the growth of pathological processes in the fi sh organism, reduces the barrier functions of tissues and mucus and, as a consequence, may induce the spread of bacterial infections. Thus, assessing the state of fi sh organism, it is necessary to take into account the analysis of the epizootic situation in water (i.e. presence of infectious and invasive diseases of fi sh, death of fi sh) as well as condition of the skin, gills and gastrointestinal tract. The results of bacteriological studies of washes from the skin, gills and intestines showed that in the conditions of farming among rainbow trout of diff erent age groups, E. 
coli, low fermented E. coli, Enterobacter spp., Klebsiella pneumoniae, Staphylococcus spp., Flavibacterium spp., Enterococcus spp. and Citrobacter spp. For the purposes of determining the sensitivity of isolated cultures to antibacterial drugs, it was found that Enterobacteriaceae are sensitive to enrofl oxacin, cotrimoxazole, doxacillin, chloramphenicol, gentamicin, ceftriaxone, cefoperazone, ceftazidime and cefpiromycin and resistant to oxytetracycline, amoxicillin and ampicillin sulbactam. E. coli also demonstrated resistance to amoxicillin and cefpirome and sensitivity to enrofl oxacin, oxytetracycline, cotrimoxazole, doxacillin, chloramphenicol, ampicillin sulbactam, gentamicin, ceftriaxone, cefoperazone, ceftazidime. Klebsiella pneumoniae was resistant to enrofl oxacin, amoxicillin and ampicillin sulbactam, while Flavobacteriaceae were resistant to amoxicillin and ampicillin sulbactam and sensitive to all other antibacterial drugs.

Key words: rainbow trout, microfl ora, skin, gills, intestines, antibacterial agents, resistance, sensitivity.