Physiological responses of Piaractus brachypomus (Cuvier, 1818) to anesthesia with linalool and thymol chemotypes of the essential oil of Thymus vulgaris

Two experiments were performed to investigate the anesthetic and physiological responses of Piaractus brachypomus exposed to linalool (EOTV-L) and thymol (EOTV-T) chemotypes of the essential oil of Thymus vulgaris (EOTV). Experiment 1 evaluated induction and recovery times of 110 juvenile fish exposed to EOTV-L (0–300 mg L⁻¹) and EOTV-T (0–200 mg L⁻¹). Experiment 2 evaluated blood collected from 120 juvenile fish immediately after exposure (IAE) and 1 h (1hAE) and 24 h (24hAE) after exposure to a control (ethanol) or to 50 or 100 mg L⁻¹ of each chemotype. EOTV-L showed a linear response plateau effect for induction (P < 0.05), with the inflection at 120.81 mg L⁻¹, and a linear effect for recovery between 94 and 385 s. EOTV-T followed a similar model for induction (inflection at 103.44 mg L⁻¹) and had a quadratic effect for recovery (minimum at 91.20 mg L⁻¹, 151 s). For EOTV- L, hematocrit was higher for the control and 100 mg L⁻¹. Glucose was decreased at 1hAE for 50 and 100 mg L⁻¹ and increased at 24hAE for 50 mg L⁻¹. Plasma protein, hemoglobin and cholesterol showed no differences. For EOTV-T, hematocrit was decreased at 24hAE and triglycerides were increased at 1hAE and decreased at 24hAE. Glucose remained stable at IAE and 1hAE for 50 and 100 mg L⁻¹. Cholesterol increased at 24hAE for the control and 50 and 100 mg L⁻¹ after 1hAE and 24hAE. Both chemotypes ensured adequate induction and recovery times at a concentration of 100 mg L⁻¹, but EOTV-L providing greater metabolic stability and less stress.