In vitro antibacterial activity of essential oils from medicinal plants against major fish pathogens in Mediterranean aquaculture

Markos N. Kolygas¹Vasiliki Kostou¹IOANNIS S. PAPPAS²Evdokia Karagouni¹Dimitra K. Toubanaki³Vasileios Bakopoulos⁴Yannis P Kotzamanis⁵Cosmas Nathanailides^6*Fotini Athanassopoulou²

• ¹Department of Aquaculture and Fish Diseases, Faculty of Veterinary Science, University of Thessaly, Karditsa, Greece
• ²Panepistemio Thessalias Tmema Kteniatrikes, Karditsa, Greece
• ³Hellenic Pasteur Institute, Athens, Greece
• ⁴Panepistemio Aigaiou Schole Periballontos, Mitilini, Greece
• ⁵Institouto Thalassias Biologias Biotechnologias kai Ydatokalliergeion, Elliniko, Greece
• ⁶University of Ioannina, Ioannina, Greece

A rise of intensive Mediterranean aquaculture has been associated with vulnerability to bacterial infections, necessitating alternative approaches to conventional antibiotics. This study evaluated the antibacterial and bactericidal activity of essential oils derived from fifteen medicinal plants against four key bacterial pathogens affecting Mediterranean marine aquaculture: Aeromonas veronii biovar veronii, Aeromonas veronii biovar sobria, Vibrio harveyi, and Tenacibaculummaritimum. Essential oils were screened using disc diffusion assays, and the most effective oils—thyme, oregano, cinnamon, and absinthe—underwent further evaluation through broth microdilution methods. Results demonstrated that these four oils exhibited notable inhibitory and bactericidal effects, with thyme and oregano showing the strongest overall activity across multiple pathogens. Notably, this is among the first studies to document the in vitro efficacy of essential oils against Tenacibaculummaritimum, a major pathogen with limited treatment options. The findings support the potential use of selected essential oils as sustainable and natural antibacterial agents in fish health management, contributing to reduced reliance on antibiotics in aquaculture.