Anaesthetic Effect of Clove Basil (Ocimum gratissimum) Essential Oil on Macrobrachium rosenbergii Post-Larvae

This study evaluated the anaesthetic potential of clove basil (Ocimum gratissimum) essential oil (EO-OG) in the post-larvae (PLs) of M. rosenbergii. The PLs were individually transferred to aquariums (500 mL) containing 50, 100, 150, 200, or 300 μL L−1 EO-OG. A sixth group of PLs was exposed to freshwater only, and a seventh group was exposed to the highest concentration of ethanol used to dilute EO-OG. Upon reaching the anaesthesia stage, the PLs were transferred to aquariums (500 mL) with freshwater only to evaluate the recovery time. The shortest sedation times were observed at 200 (15.98 s) and 300 μL L−1 (25.85 s). The shortest anaesthesia time was observed at 200 μL L−1 (22.52 s). The longest recovery time was observed at 100 μL L−1 (1367.10 s); the shortest recovery time was observed at 150 μL L−1 (630.10 s). No mortality or adverse effects were observed in any experimental group. The concentration of 150 μL L−1 resulted in sedation (49.24 s), anaesthesia (80.10 s), and recovery (630.10 s) times within those suggested as adequate for freshwater prawn farming. This research demonstrated the sedative and anaesthetic properties of EO-OG and its potential application in prawn farming. This study recommends using 150 μL L−1 of EO-OG in M. rosenbergii PLs.