Chemical composition and in vitro/in vivo antisaprolegniosis efficacy of Satureja Bachtiarica and Achillea Talagonica essential oils on rainbow trout eggs

The rising prevalence of fungal infections in aquaculture, combined with the high cost, adverse side effects, and increasing resistance associated with synthetic antifungal agents, has stimulated interest in natural alternatives. This study investigated the chemical composition and antifungal activity of essential oils derived from Satureja bachtiarica Bunge and Achillea talagonica Boiss against Saprolegnia parasitica, the causative agent of saprolegniosis. Gas chromatography- mass spectrometry analysis revealed that the predominant constituents of the S. bachtiarica essential oil were carvacrol (71.61%), γ-terpinene (12.71%), p-cymene (7.01%), α-terpinene (1.74%), and β-bisabolene (1.39%). In contrast, the main components of A. talagonica oil included camphor (25.26%), chrysanthenone (23.68%), α-pinene (11.85%), 1,8-cineole (6.25%), caryophyllene oxide (5.20%), and camphene (3.27%). Both essential oils demonstrated significant antifungal activity. The minimum inhibitory concentrations were 1.56 µL/mL and 3.12 µL/mL, while the minimum fungicidal concentrations were 3.12 µL/mL and 6.25 µL/mL for S. bachtiarica and A. talagonica, respectively. In vivo assays demonstrated that both essential oils significantly inhibited the transmission of S. parasitica from contaminated to healthy eggs, yielding survival rates of 88.84% for S. bachtiarica and 80.40% for A. talagonica, compared with 75.83% in the untreated control group. During incubation, the essential oils also prevented contamination, resulting in survival rates of 89.40% and 87.43%, respectively, relative to 85.33% in the control group. These findings indicate that these essential oils are promising natural alternatives to conventional antifungal agents such as malachite green and formalin. However, further studies are necessary to fully evaluate their environmental safety and potential impact on non-target organisms.