Anesthesia with eugenol and menthol for Piaractus brachypomus (Cuvier, 1818): Induction and recovery times, ventilation frequency and hematological and biochemical responses

This work evaluated the use of eugenol and menthol as anesthesia for juvenile Piaractus brachypomus. Experiment I determined the times for anesthesia induction and recovery using different concentrations of eugenol and menthol (0, 25, 50, 75, 100 and 125 mg L-1), as well as their effects on ventilation frequency (VF) for two size classes: Juveniles I - 0.87 +/- 0.20 g and Juveniles II - 17.14 +/- 3.27 g for eugenol and Juveniles I - 0.83 +/- 21 g and Juveniles II - 16.83 +/- 2.78 g for menthol. Based on data from Experiment I, Experiment II evaluated the effects of 0, 25 (beyond the recommended times for induction and recovery) and 50 mg L-1 (within the recommended times for induction and recovery) of eugenol and menthol (independent tests) on hematological and biochemical parameters of fish measured at two blood collection times (1 h post-induction and 24 h post-recovery). Sixty juveniles weighing 16.92 +/- 3.34 g and 60 juveniles weighing 18.49 +/- 3.07 g were used to evaluate eugenol and menthol, respectively. Survival was 100% at 24 h after the end of Experiment I. Eugenol concentrations between 50 and 100 mg L-1 were able to induce deep anesthesia for both juvenile size classes, while menthol was able to induce deep anesthesia at concentrations between 25 and 100 mg L-1 for Juveniles I and between 50 and 125 mg L-1 for Juveniles II. The use of 50 mg L-1 of eugenol was able to reduce VF during recovery and prevent an increase in plasma glucose while having little influence on hematological and biochemical parameters after handling. The use of 50 mg L-1 of menthol also reduced VF during recovery and did not cause changes in blood parameters that would be harmful to fish physiology.

Automated summary

This study demonstrated that concentrations of 50-100 mg L-1 of eugenol and 25-100 mg L-1 of menthol are able to induce deep anesthesia in juvenile Piaractus brachypomus. These concentrations had minimal impact on blood parameters.