The Effects of Origanum vulgare L. Essential Oils on Anaesthesia and Haemato-Biochemical Parameters in Mozambique Tilapia (Oreochromis mossambicus) Post-Juveniles

This study investigated the effects of oregano (Origanum vulgare) essential oil (OEO) anaesthesia and stress-related physiological parameters in tilapia mossambicus (Oreochromis mossambicus) post-juveniles. Fish were subjected to different concentrations of OEO (25, 50, 100, and 150 μL L−1) to assess the effects of the anaesthesia and recovery time. A second experiment subjected fish to other handling treatments, including a control (no OEO exposure), ethanol solution, 25 μL L−1 (low effective anaesthesia concentration of OEO), and 100 μL L−1 high effective anaesthesia concentration of OEO) for 10 min to assess the haemato-biochemical indices and survival rate at 0 h and after 24 h. Moreover, all the tested OEO concentrations induced anaesthesia in the studied fish, where the anaesthesia induction time decreased with increased OEO concentrations. Meanwhile, the inverse was reported for recovery time. Based on the ideal anaesthetic criteria, 50 μL L−1 and 100 μL L−1 were the suitable concentrations that could be recommended for quick anaesthesia. However, according to the haemato-biochemical parameters and survival results, 25 μL L−1 was safe to anaesthetise tilapia mossambicus for 10 min and could be recommended for time-consuming fish-handling procedures. Future studies should investigate multiple factors that influence anaesthesia in fish for better optimisation of OEO in tilapia mossambicus.