ABSTRACT This study aimed to verify the sedative and anaesthetic effect of the essential oils of basil (Ocimum basilicum) (EOOB) and lemongrass (Cymbopogum flexuosus) (EOCF) in Nile tilapia juveniles.

The fish were transferred to aquaria containing different concentrations of each essential oil:

10, 25, 50, 100, 200, 400 and 600 μL L-1. The time of sedation ranged from 7 to 31 seconds and the recommended concentration was 10 or 25 μL L-1 for both essential oils. The best times for anaesthesia and recovery were found for the concentrations of 400 μL L-1 for EOOB (135.2 and 199.1 seconds, respectively) and 600 μL L-1 for EOCF (327.1 and 374.8 seconds, respectively). In conclusion, we recommend the use of EOOB and EOCF for the sedation and anaesthesia of Nile tilapia at concentrations of 10-25 (for both), 400 and 600 μL L-1, respectively.