The objective of this work was to evaluate eugenol as anesthetic for Nile tilápia. For the best concentration of the anaesthetic, six treatments (50, 75, 100, 150, 200, and 250 mg L-1) were evaluated, with ten fishes per treatment, anesthetised individually and monitored during the induction and recovery. Toxicity was estimated in 210 fish submitted to seven eugenol concentrations (50, 75, 100, 150, 200, 250, and 300 mg L-1) for 600 s; and for safety margin, 120 fish were submitted to 75 mg L-1 for five time intervals (600, 1,200, 1,800, and 2,400 s). The effective concentrations were 50 and 75 mg L-1. Lethal concentration (LC) values for 600 s were: LC01 81.97 mg L-1, LC50 184.26 mg L-1, and LC99 286.55 mg L-1. Times of lethal concentration (TLC) were TLC01 566.97 s, TLC50 1,611.66 s, and TLC99 2,656.34 s. For fast deep anesthesia, 75 mg L-1 of eugenol is recommended, with a safety margin of 484,27 s; for long period anesthesia (600 s) 50 mg L-1 were recommended. The higher therapeutic concentration costs R$ 0.065 per liter. Eugenol was effective for euthanasia at 286.55 mg L-1 for 600 s.
Oreochromis niloticus; anesthesia; cost; safety
