Antimicrobial activities of phytochemicals--cinnamaldehyde (TC), ferulic acid (FA), -coumaric acid (-CA), caffeic acid (CA), chlorogenic acid (CHA), essential oil (TO), essential oil (ECO), and oil (TTO) against species-were assessed. Growth of all subsp. and almost all strains was inhibited by TC at concentration 0.01 mg/mL, and for most strains minimal inhibitory concentrations (MIC) ranged from 0.01 to 0.19 mg/mL. The inhibitory effect of TC against subsp. was comparable to the effect of oxytetracycline, and in the case of subsp. and was higher compared to gentamicin. MIC of FA, -CA, and CA for most strains ranged from 1.56 to 3.12 mg/mL, and MIC values of TO for most strains ranged from 0.39 to 0.78 mg/mL. TO and TC at the concentrations below ½ MIC values used in mixtures exhibited strong synergism. ECO and TC showed synergy in mixture of ⅛ MIC of ECO and ¼ MIC of TC. TC and TO exhibited the strongest inhibitory and bactericidal effect against investigated species, and they are a promising alternative to the use of antibiotics in controlling the growth of these fish pathogens.