Peppermint essential oil as an anesthetic for and toxicity to juvenile silver catfish

The objective of this work was to evaluate peppermint (Mentha piperita) essential oil toxicity to and potential as an anesthetic for juvenile silver catfish (Rhamdia quelen). To determine the lethal concentration at 4 hours (LC50-4h), 210 fish (3.08±0.8 g and 7.59±0.67 cm) were exposed to 0, 20, 50, 80, 110, and 140 mg L-1 essential oil. To evaluate the anesthetic potential, nine fish were individually exposed to each oil concentration (50, 80, 110, and 140 mg L-1) used. Water quality parameters were controlled. The mortality rate and the severity and extent of the gill injuries of silver catfish juveniles at 4 hours of exposure increased with increasing peppermint essential oil concentrations, with LC50-4h estimated to be 75.06 mg L-1. The main gill injuries were: congestion of the venous sinus of the primary lamella and at the base of the secondary lamella; interlamellar hyperplasia with fusion of lamellae; epithelial detachment; dilation of the venous sinus; edema adjacent to the lamella; and aneurysm. However, this oil is an effective anesthetic for silver catfish juveniles at the concentration of 80 mg L-1, with a short time of anesthesia (<4 min) and recovery (<10 min), with no mortality.