Anesthetic potential of the essential oils of Aloysia triphylla, Lippia sidoides and Mentha piperita for Colossoma macropomum

The aim of this study was to evaluate the anesthetic potential of the essential oils of Aloysia triphylla (EOAT), Lippia sidoides (EOLS) and Mentha piperita (EOMP) in relation to juvenile tambaqui (Colossoma macropomum), based the swimming behavior of these fish and possible histopathological damage to the gills. To induce anesthesia, juvenile tambaqui (130.55 ± 22.4 g; 16.8 ± 0.95 cm) were individually exposed to different concentrations of the essential oils (EOAT: 5, 10, 20, 40, 60, 80 and 150 mg L−1; EOLS: 2, 5, 10, 20, 30, 40 and 50 mg L−1; EOMP: 5, 10, 20, 40, 60, 70 and 90 mg L−1), for exposure periods of between four minutes and six hours. The three essential oils evaluated presented anesthetic properties. The concentration intervals over which the fish reached all the stages of anesthesia (1, 2, 3a, 3b and 4) were between 40 and 150 mg L−1 for EOAT; 20 and 50 mg L−1 for EOLS; and 40 and 90 mg L−1 for EOMP. The times taken to reach the anesthesia stages were inversely proportional to the increases in the concentration of the essential oils. The histopathological damage to the gills of the tambaqui that resulted from using essential oil concentrations that were defined as anesthetic (150 mg L−1 EOAT, 30 mg L−1 EOLS and 90 mg L−1 EOMP) were also evaluated. The main damage recorded was hypertrophy and hyperplasia of the lamellar epithelium, lamellar fusion and proliferation of chloride cells. According to the histopathological alteration index (HAI), there were no irreversible damage (such as fibrosis and necrosis) to the gills of the tambaqui. However, while EOLS and EOMP caused mild damages in the gills, the EOAT generated more severe damages. Overall, for the tambaqui, the essential oils of A. triphylla, L. sidoides and M. piperita are efficient anesthetic in the doses of 150, 30 and 90 mg L−1, respectively. •This study reports the sedative and anesthetic effects of Aloysia triphylla, Lippia sidoides and Mentha piperita essential oils on Colossoma macropomum.•The essential oil of L. sidoides (30 mg L-1) induced faster anesthesia and recovery in C. macropomum.•Essential oils of A. triphylla, L. sidoides and M. piperita caused no irreversible damage to the gills of C. macropomum.