The Lophiosilurus alexandri is an important species to the Brazilian aquaculture. Moreover, the studies about the effects of essential oil (EO) of Aloysia triphylla in fish are almost absent. Thus, the aims of this study were: 1) to investigate the anesthetic effect of the EO of A. triphylla and, 2) if this EO improves the physiological parameters of L. alexandri after transport. The experiment was divided in three steps: 1) the anesthesia induction with the EO of A. triphylla (in μL/L): 25, 50, 100, 200, or 400; 2) transport for 4 h with the fish separated into three groups: control and two EO concentrations of A. triphylla (in μL/L): 12.5 and 25; and, 3) determination of the ventilatory frequency (VF) in fish exposed to this EO at 12.5 or 25 μL/L. The results showed that the increasing concentration of A. triphylla EO proportionally decreased the time required for sedation and anesthesia induction and increased recovery time. After transport, some alterations in water and blood parameters were observed independently of the treatment and lower VF was found in fish exposed to 25 μL/L of A. triphylla EO. Taken together these results indicated that this EO decreased fish metabolism. Finally, A. triphylla EO was an efficient anesthetic in L. alexandri, mainly at 400 μL/L and, both EO concentrations used in the transport contributed to improve water and physiological parameters.