Antifungal effects of alcoholic extract of Thymus vulgaris on Siberian sturgeon (Acipenser baerii) eggs compared with malachite green effects

The economic losses due to fungal contamination in development of sturgeon and the side effects of malachite green in the environment are very important. Therefore, it is essential to investigate and introduce suitable natural substances instead of malachite green. The aim of this study was to compare antifungal effect of Thymus vulgaris with malachite green on fungi isolated from Siberian sturgeon eggs obtained from International Sturgeon Research Institute. The samples were inoculated in culture media (SDA) and Glucose-Peptone Agar at 25°C for 5-7 days and then isolated fungi were identified. The antifungal effect of T. vulgaris extract was evaluated by disc diffusion method and MIC and MFC of fungi was measured. In this study, Saprolegnia spp., Fusarium spp., Rhodotorula spp., Penicillium spp., Trichoderma spp., Chrysosporium spp. and sterile hyphae were isolated and identified from fertilized eggs of A. baerii. According to the results, T. vulgaris extract had a significant effect on all isolated fungal species. The most effective sample was observed on Saprolegnia and the least effective ones were Fusarium and Trichoderma. The MIC and MFC of alcoholic extract for Saprolegnia spp., Fusarium spp., Rhodotorula spp., Penicillium spp., Trichoderma spp., Chrysosporium spp., sterile hyphae were ≥0.75, 3, 1.5, 1.5, 0.75, 1.5, ≤0.75 mg/ml, and ≥1.5, ≥3, 3, 3, 1.5, 3 and 1.5 mg/ml, respectively. Due to high frequency of Saprolegnia spp. in A. baerii eggs, and the significant effect of alcoholic extract of T. vulgaris, it could be used as a good alternative for malachite green to reduce the frequency of fungal contamination and its economic losses during reproductive seasons of A. baerii.