Thymol and linalool chemotypes of the essential oil of Thymus vulgaris (thyme) as anesthetic for Colossoma macropomum: Physiology and feed consumption

This study evaluated the use of two chemotypes of the essential oil of Thymus vulgaris (EOTV) as anesthetics for Colossoma macropomum and their influence on physiology and feed consumption. Three experiments were per-formed using thymol (EOTV-T) and linalool (EOTV-L) chemotypes. Experiment 1 determined anesthesia in-duction and recovery times for juveniles exposed to different concentrations of EOTV-T and EOTV-L (0, 50, 100, 150, 200 and 300 mg/L). Based on the results of Experiment 1, two more experiments were performed. Experiment 2 evaluated the effects of 0 mg/L EO (only the solvent ethanol), 50 mg/L EOTV-T and 100 mg/L EOTV-L on blood parameters after induction and one hour after recovery. Experiment 3 evaluated the effects of 0 mg/L EO, 50 mg/L EOTV-T and 100 mg/L EOTV-L on feed consumption after handling. No mortality was observed in any of the experiments. In Experiment 1, increasing concentrations of EOTV-T and EOTV-L reduced anesthesia induction time and increased recovery time; EOTV-T induced anesthesia faster than EOTV-L. Experiment 2 found control hemoglobin levels to be above baseline after one hour of recovery; no difference was observed for hematocrit and total plasma protein. Soon after induction, the control treatment had higher glucose levels than the other treatments. After one hour of recovery, the EOTV-T and EOTV-L treatments had increased glucose levels, while those of the control treatment were reduced. Soon after anesthesia, juveniles anesthetized with EOTV-L had the lowest cholesterol level, while those anesthetized with EOTV-T had the highest level of triglycerides. Experiment 3 found no difference in feed consumption among treatments. The lowest feed consumption was in the first days after handling for all treatments, which increased over subsequent days of the experiment. It was concluded that EOTV-T and EOTV-L are promising anesthetics for juvenile C. macropomum and that the use of 50 mg/L EOTV-T and 100 mg/L EOTV-L causes anesthesia in these juveniles within ideal induction and recovery intervals. The use of EOTV-T and EOTV-L did not greatly influence blood parameters and did not affect feed consumption after handling.