Plectranthus amboinicus is an aromatic herb often used in traditional medicine due to its antimicrobial properties. Based on it, the present study aimed to assess the toxic, antioxidant and, antibacterial properties of P. amboinicus essential oil (EO) either separated or mixed into fish feed. The chemical composition of the EO was also investigated. All samples were prepared with over 50% of carvacrol. The results revealed that the EO is a weak antioxidant and highly toxic against Artemia salina, showing greater antibacterial activity than positive control of chloramphenicol and synergistic effects. The EO also presented high antimicrobial activity against Aeromonas hydrophila strains when free or feed-incorporated, thus being a promising product for the treatment of opportunistic infections in fish.

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