To evaluate the influence of benzocaine concentration on the induction and recovery from anesthesia in different sized Nile tilapia (Oreochromis niloticus), it was developed a random block experiment design in 4 × 4 factorial consisted of four fish lengths (6; 10; 14 and 18 cm total lenght) and four benzocaine concentrations (60; 120; 180 and 240 mg of benzocaine per liter of water). The induction and the recovery from anesthesia were divided in three stages based on the behavior of the fishes under anesthetic effect. The time spent in each stage was recorded. Differences in length did not affect significantly the anesthesia and recovery time. Linear plateu regressions were generated to estimate the point which increases on anesthetic doses does not imply in further effects. During the anesthesia induction, the plateu occurred in concentration time of 132 mg/L, and estimated time of 86 seconds would be necessary to achieve the complete sedation (stage 3). For permanence of the fish under total sedation, it is needed 190 g/L benzocaine and estimated time of permanence in this stage is 91.1 seconds. Benzocaine concentrations above 190 mg/L do not produce any additional effects that justify its use.
anesthetic; aquaculture; length; stage
