Eugenol anesthesia in African clawed frogs (Xenopus laevis) of different body weights

The objective of this prospective study was to determine the duration of anesthesia in Xenopus laevis frogs of different body weights relative to exposure time in a eugenol (350 microL/L) bath. Two groups of 5 female frogs each weighing 7.5 +/- 2.1 g (small frogs) or 29.2 +/- 7.4 g (medium frogs) were used. The acetic acid test (AAT), withdrawal reflex, righting reflex, heart rate, and blood oxygen saturation were used to evaluate CNS depression after eugenol bath administration. No responses to the AAT, withdrawal reflex, and righting reflex were seen for 1 h (small frogs) or 0.5 h (medium frogs) after immersion in a eugenol bath for 5 or 10 min, respectively. Oxygen saturation was not affected by anesthesia, but heart rate was depressed for as long as 1 h in both groups of frogs. Surgical anesthesia evaluated by using skin and abdominal incisions revealed that small frogs were anesthetized for a maximum of 15 min compared with 30 min in medium frogs. Frogs showed no ill effects 24 h after eugenol bath administration. These results suggest that body weight is an important parameter to consider when using a eugenol bath for anesthesia of Xenopus frogs.