Use of the essential oil of Thymus vulgaris (thyme) and its nanoemulsion as an anesthetic during the cultivation of tambaqui (Colossoma macropomum): anesthesia induction and recovery curve, physiology, performance, and feed consumption

The thymol chemotype of the essential oil of Thymus vulgaris (EOTV-T) and its nanoemulsion (NEOTV-T) were investigated as anesthetics in the management of Colossoma macropomum. The stability of nanoemulsions was analyzed by zeta potential and dynamic light scattering for an interval of 37 days prior to carrying out two anesthesia experiments. The first experiment determined anesthesia induction and recovery intervals for juveniles anesthetized with different concentrations of EOTV-T and NEOTV-T. Based on the obtained induction and recovery curve, the second experiment adopted concentrations of 75 mg/L of EOTV-T and 50 mg/L of NEOTV-T for use during biometric management every 10 days for 60 days of cultivation of juvenile C. macropomum. The results showed that NEOTV-T had an average diameter of less than 100 nm for up to 22 days and was more effective at inducing anesthesia than EOTV-T. The continuous use of anesthetics during biometrics did not affect juvenile performance in terms of growth, feed consumption, and survival. Furthermore, no significant differences were observed in hematological and biochemical parameters between juveniles of the control treatment and those subjected to biometric management using 75 mg/L of EOTV-T and 50 mg/L of NEOTV-T. It can be concluded that the essential oil of T. vulgaris and its nanoemulsion can be used to facilitate the management of juvenile C. macropomum without compromising their performance or well-being.