Use of the essential oil of Thymus vulgaris (thyme) and its nanoemulsion as sedatives during tambaqui (Colossoma macropomum) transport: water quality, survival and physiology

This study investigated the use of the essential oil of Thymus vulgaris (EOTV) and its nanoemulsion (NEOTV) as sedatives during the transport of juvenile Colossoma macropomum (30.2 +/- 3.90 g and 11.8 +/- 0.8 cm). The EOTV was characterized by gas chromatography, while the NEOTV was prepared by sonication and characterized by zeta potential. Six treatments were evaluated: a basal treatment with blood collection from 10 juveniles without transport management, and five treatments with transport, with three replicates each (transport bags), containing the following: 0 (control), 10 mg/L of EOTV, 20 mg/L of EOTV, 10 mg/L of NEOTV and 20 mg/L of NEOTV. The juveniles were transported for 4 h in 10-L plastic bags with 6 L of water and pure oxygen supplementation, at a density of 10 juveniles per bag. Water quality parameters were measured immediately after opening the bags post-transport. Blood samples were collected from 10 juveniles from each treatment immediately at 24 h and 72 h after transport. The EOTV presented p-cymene (47.63%) and carvacrol (30.44%) as major components, and the NEOTV presented particles with an average diameter of less than 100 nm. There was no mortality during the experiment. The water in the bags of juveniles transported with 20 mg/L of EOTV, 10 mg/L of NEOTV, and 20 mg/L of NEOTV presented lower temperatures than the control. In addition, the water in the bags with 20 mg/L of NEOTV presented higher concentrations of dissolved oxygen than the control. Juveniles transported with 20 mg/L of EOTV, 10 mg/L of NEOTV, and 20 mg/L of NEOTV exhibited lower hemoglobin, hematocrit, and glucose levels after transport. It is concluded that, overall, NEOTV is more effective than EOTV. The use of 20 mg/L of NEOTV in the water is recommended to reduce oxygen consumption and avoid hyperglycemia during the transport of juvenile C. macropomum.