Parasiticidal Activity of Citral Against Enteromyxum leei (myxozoa: myxosporea) in Olive Flounder (Paralichthys olivaceus)

Myxosporean parasites pose a serious challenge in the aquaculture industry, particularly for species such as olive flounder (Paralichthys olivaceus). Infected fish can experience a range of health issues including stunted growth, degraded flesh quality, and a high mortality rate, significantly impacting farmers and the entire industry. This study explored the effectiveness of essential oil as potential parasiticidal agents against myxosporean parasite infections in olive flounder. Using molecular techniques, we identified Enteromyxum leei as the causative agent of myxosporean parasite infection, and screened essential oils for parasiticidal activity. Fluorescence microscopy revealed that treatment with one essential oil, citral, at 100 µg/mL achieved a parasiticidal rate of ~ 20% after 6 h, which increased to ~ 85% after 12 h of treatment. The parasiticidal rate with 250 µg/mL citral was ~ 60% after 6 h and 100% after 12 h. The results suggest that citral treatment at 100 µg/mL or higher for durations exceeding 12 h could effectively kill E. leei parasites. This study provides a molecular-based technique for determining E. leei infectivity in flounder, and highlights the promising parasiticidal properties of citral as a potential therapeutic agent in aquaculture management strategies. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.