Eugenol and Lippia Alba Essential Oils as Effective Anesthetics for the Amazonian Freshwater Stingray Potamotrygon Wallacei (Chondrichthyes, Potamotrygonidae)

Abstract This study assessed the potential of eugenol and the essential oil of Lippia alba (EOLA) in providing suitable anesthetic induction and recovery times, and their consequent effects on the blood and respiratory physiology, as well as the gill architecture of an Amazonian freshwater stingray, Potamotrygon wallacei, at the onset of the anesthetic event and after 48 h of recovery. Juveniles of P. wallacei (n = 12) were exposed to increasing concentrations of eugenol (75, 100, 125 and 150 µL L− 1) and EOLA (150, 175, 200 and 225 µL L− 1) in an immersion bath. Anesthetic induction was found to be faster with the use of eugenol compared to EOLA. On the other hand, the stingrays anesthetized with eugenol displayed a longer recovery time than those exposed to EOLA. The highest concentrations of eugenol caused moderate to severe histological changes in the gills. No significant changes were found for hematocrit and plasma metabolites in the stingrays anesthetized with all concentrations of both eugenol and EOLA just after the onset of anesthetic action, when compared to those recovered after 48 hours. Investigations regarding the potential use of these natural anesthetics are unprecedented for freshwater stingray species and 200 µL L− 1 EOLA is recommended as the most suitable anesthetic for use in juveniles of P. wallacei.