Efficacy of Synthetic Eugenol as an Anesthetic for Nile Tilapia (Oreochromis niloticus Linn.)

Abstract

The efficacy of synthetic eugenol as an anesthetic for Nile tilapia (Oreochromis niloticus Linn.) fry was investigated. An acute toxicity test and the efficacy of synthetic eugenol as an anesthetic were studied and compared with clove oil-derived eugenol and MS-222 under similar conditions. The acute toxicity test indicated that the 24-hr LC50 value of synthetic eugenol, clove oil-derived eugenol and MS-222 was 16.98, 16.95 and 72.5 ppm, respectively. The efficacy test, involving 20 min exposure to various concentrations of the three anesthetics indicated that synthetic and clove oil-derived eugenol caused sedation at 5 ppm. A dose of 20 ppm of synthetic eugenol caused the loss of reflex reactivity (stage 5 of anesthesia) with the induction time (3.40 min) slightly over the limit of 3 min, while it took 2.86 min for clove oil-derived eugenol. A higher dose of MS-222 was required than for the two other anesthetics, with 30 ppm necessary to induce the sedation stage and 120 ppm to induce stage 5 anesthesia within 2.16 min. However, this concentration caused 50% mortality after 20 min of exposure. The recovery time from anesthesia for fish exposed to each anesthetic was prolonged according to the higher dose exposure of each anesthetic. The results of this experiment clearly indicated that synthetic eugenol could be an effective anesthetic for handling and transport purposes of this species judging from the concentration for the induction of various stages of anesthesia, recovery time and safety for tilapia fry.