Comparative efficacy of benzocaine, tricaine methanesulfonate and eugenol as anesthetic agents in the guppy Poecilia vivipara

The aim of this study was to evaluate the anesthetic efficacy and determine the lowest effective concentration in the guppy, Poecilia vivipara. Fishes were exposed to benzocaine, tricaine methanesulfonate and eugenol at three different concentrations. After induction, they were transferred to an aquarium free of anesthetic for evaluating their recovery time. At the lowest concentration of the three anesthetics (50 mg L-1), fish did not reach complete induction. Time to accomplish a light sedation stage was significantly negative-related with concentration using tricaine (145 +/- 13.4 s with 50 mg L-1 to 4.7 +/- 0.7 s with 200 mg L-1) and benzocaine (152.8 +/- 13 s with 50 mg L-1 to 4.0 +/- 0.9 s with 200 mg L-1). For eugenol, significant differences were found between the lowest concentration, 50 mg L-1 (241 +/- 57.6 s) with 100 mg L-1 (13.3 +/- 3.9 s) and 200 mg L-1 (9.5 +/- 2.6 s). Recovery times were significantly longer (P < 0.05) with the increase of eugenol concentration from 100 mg L-1 to 200 mg L-1, with no differences found between the different concentrations of benzocaine and tricaine. Complete induction times were significantly greater (P < 0.05) when using eugenol comparing with the other two anesthetic agents in fish exposed at the highest concentrations (200 mg L-1). This parameter showed a great dispersion when using eugenol at this concentration. Three fish exposed to 200 mg L-1 of eugenol did not recovered from the anesthetic after 180 s and presented ventilatory failure. Significantly shorter recovery times (P < 0.05) were found using tricaine comparing with eugenol (120 +/- 24.8 s and 163.5 +/- 57.1 s, respectively) at the higher concentration (200 mg L-1). The optimum dose rates of benzocaine and tricaine for induction within the efficacy criteria stated in this study was 200 mg L-1. It can be concluded these anesthetics are the more effective ones, being benzocaine more economically affordable for large-scale use on handling P. vivipara.