Determination of the optimal dose of benzocaine hydrochloride in anesthesia of tilápia (Oreochromis niloticus)

Abstract

Fish anesthesia is indicated for several management procedures such as capturing, biometry, tagging, transporting, physical examination, reproductive management and surgical procedures. In this study the dose of benzocaine hydrochloride necessary for tilápia (Oreochromis niloticus) anesthesia was determined through six phases with 240 fish. In each phase 40 fish were evaluated. The interval between phases was two months. Mean values for weight and (allometric condition factor), in each phase, were 25.64 (2.56), 167.58 (2.88), 286.12 (2.57), 388.24 (2.50), 518.19 (2.89), 592.71 (2.67), respectively. The values for allometric condition factors showed that the animals included in the experiments were in good body conditions (P > 0.05). In each phase, fishes were captured and kept in four containers with five liters of water and benzocaine hydrochloride diluted in 20 mL of ethanol, in concentrations of 100, 140, 180, and 220 mg/liter of water. The time of induction in seconds (TI) was registered for each fish, and after the anesthetic induction the biometric analysis was conducted at fixed time of 10 minutes. After, the fishes were transferred to containers with 20 liters of water under constant flow, in order to evaluate the recovering time in seconds (TR). At each phase the minimum dose of benzocaine hydrochloride concentration was calculated using LRP (Linear Response Plateau). The model included the dose of benzocaine (mg/L) and the time of induction in seconds. The values of LRP were, respectively, 146.60 and 67.45, 155.95 and 76.33, 160.45 and 87.42, 167.00 and 108.14, 165.87 and 174.03, 164.00 and 139.80. The optimum dose was related to the mean weight in each phase, resulting in the equation: Dose = 149.65 + 0.03183 x weigh (r2 = 0.73). This equation showed that an increase of 1g in the body weight corresponded to an increase of 0.032 mg/L in the dose of benzocaine hydrochloride.