Benzocaine and menthol as anesthetics for the African cichlid Aulonocara nyassae

Abstract

The objective of this study was to investigate the effects of benzocaine and menthol on the anesthesia of Aulonocara nyassae juveniles. Two size classes of fish were used in trials with benzocaine: Juveniles I—70 fish of 0.74 ± 0.31 g (39.41 ± 7.48 mm); and Juveniles II—70 fish of 3.80 ± 0.92 g (76.58 ± 9.83 mm). The fish used for trials with menthol were as follows: Juveniles I—70 fish of 1.01 ± 0.39 g (50.39 ± 12.75 mm) and Juveniles II—70 fish of 3.73 ± 0.78 g (64.94 ± 8.98 mm). Seven concentrations—0, 12.5, 25.0, 50.0, 75.0, 100.0, and 125.0 mg L−1—of each anesthetic (benzocaine and menthol) were tested on each size class of fish (n = 10 fish per size class and anesthetic concentration). Thus, anesthesia induction time and recovery were evaluated. Concentrations of 12.5 and 25 mg L−1 of benzocaine did not lead to a deep stage of anesthesia in the animals; however, the other concentrations presented anesthetic effect. For menthol, the concentration of 12.5 mg L−1 also did not anesthetize the fish. However, the other doses were effective and safe. The recommended anesthetic concentrations provided induction and recovery times within the limits considered ideal for fish. Concentrations between 75 and 125 mg L−1 of benzocaine for Juvenile I and 50 to 125 mg L−1 for Juvenile II are recommended. For menthol, concentrations between 50 and 125 mg L−1 can be used for both size classes of A. nyassae.