Physiological and pharmacokinetic responses in neotropical Piaractus mesopotamicus to the essential oil from Lippia sidoides (Verbenaceae) as an anesthetic

Abstract

The goal of the study was to evaluate <em>Lippia sidoides</em> essential oil as an anesthetic for the tropical fish pacu <em>Piaractus mesopotamicus</em>. The physiological and pharmacokinetic responses were evaluated during fish handling. Fish were exposed to different concentrations of the essential oil (20, 30, 40, 50, 60, and 70 mg L−1) to determine the induction times to anesthesia. The hematological parameters were determined in fish exposed to different concentrations of the essential oil (20 and 70 mg L−1), which were enough to induce light and deep anesthesia in 10 min. For pharmacokinetics purposes, blood samples were collected after exposure to the essential oil (70 mg L−1) for 10 min at different depuration times (0, 15, and 30 min, 1, 2, 4, 6, 8, 24, and 48 h). Thymol was the major essential oil compound in <em>Lippia sidoides</em>, at 61.12%. All physiological parameters returned to control values in 24 h. Distribution and elimination of the major compound in the blood plasma were fast, being 64.31% in 1 h. The distribution constant of the essential oil was 7.59 µg h−1 (k) in the organism. Therefore, when the plasmatic concentration of thymol was reduced, this constant decreased to 0.44 µg h−1(k). The AUC value was 38.05 µg h−1, the initial half-life during the distribution stage (<em>T</em>1/2 α) was 0.09 h and the elimination half-life (<em>T</em>1/2β) was 1.59 h. Fish survival was 100% even 20 days after the experiments. Therefore, <em>Lippia sidoides</em> essential oil may be considered a safe anesthetic for tropical fish.