Determination of Optimal Doses and Minimum Effective Concentrations of Tricaine Methanesulfonate, 2-Phenoxyethanol and Eugenol for Laboratory Managements in Nile Tilapia (Oreochromis niloticus)

SIMPLE SUMMARY: Fish studies often require anesthetic drugs to render the fish amenable for experimental handling and to secure animal welfare. However, the optimal dose is not always available. In this study, we determined the optimal does of three commonly used anesthetics, eugenol (EUG), tricaine methanesulfonate (MS-222), and 2-phenoxyethanol (2-PE), for induction of surgical anesthesia in marketable-size Nile tilapia, and decided on their minimum effective concentrations (MEC) in the fish serum. The results revealed that the optimal doses of EUG, MS-222, and 2-PE were 90, 300, and 900 ppm, and their MECs were 53, 70, and 263 µg/mL, respectively. Increasing the anesthetic doses generally resulted in the shortening of the induction times, but variably affected the recovery times. In contrast, the MECs were found to be independent of the administered doses. After the dosing was stopped, the serum concentrations of anesthetics decreased rapidly, lowering by >90% within the first hour and by >99% after 4 h. Our research provides practical information for a smooth fish handling and offered insights for designing researches requiring surgical anesthesia. ABSTRACT: Anesthetic agents are often used in fish experiments to reduce the stress and struggle and to improve animal welfare. The present study aimed to determine the optimal doses and serum minimum effective concentration (MEC) of tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE), and eugenol (EUG) in Nile tilapia. Twenty-one fish were immersed in three different doses of each anesthetic and the minimal dose that produce stage III anesthesia within 5 min, maintain anesthesia status for 3 min, and recover within 5 min was considered the optimal dose. The serum concentrations of anesthetics immediately after the fish reached stage III anesthesia was defined as the MEC. The results revealed that the anesthetics dose-dependently shorten the induction time while the effect of doses on the recovery times were variable. The determined optimal doses for MS-222, 2-PE, and EUG were 300, 900, and 90 ppm, respectively. The MECs were 70, 263, and 53 µg/mL, respectively, about two to four times lower than the optimal doses and were independent of the doses. After immersion stopped, the serum concentrations decreased by >90% within the first hour and >99% after 4 h. Our research provides useful information for a smooth fish handling and design for researches requiring stage III anesthesia.