Essential Oil of Varronia curassavica (Cordiaceae) as an Anesthetic and Sedative for Zebrafish

In many research studies, the handling and procedures performed can generate stress and require the use of anesthesia or sedation. In this sense, plant-based extracts named essential oils have emerged as potentially effective and environmentally safe anesthetic/sedative options. Here, we sought to evaluate the essential oil of Varronia curassavica (VCEO) as an anesthetic/sedative ingredient. Here, the anesthetic and sedative capabilities of the VCEO using adult zebrafish ( Danio rerio ). The anesthetic induction was performed under four different concentrations (100, 200, 400, and 600 mg L ⁻¹ ), followed by evaluation of recovery time; furthermore, a 3 h long exposure was performed for sedative testing, where fish were exposed for 3 h at three different concentrations (50, 80, and 100 mg L ⁻¹ ) under a superpopulation condition, such as those faced during transport. To assess stress, we collected whole-body cortisol from each individual after each exposure. The concentrations of 400 and 600 mg L ⁻¹ induced anesthesia (S4) but promoted excessive recovery times; on the contrary, they reduced the cortisol levels of the fish compared with the positive and negative controls. In the sedative testing (3 h long exposure), the animals exposed to 50 mg L ⁻¹ remained in S2 stage from the first 10 min, and those exposed to 80 mg L ⁻¹ after 20 min. The 100 mg L ⁻¹ induced stage S3a. There were no significant changes in cortisol levels observed at these concentrations. Limitations include measurement of whole-body cortisol at a single endpoint and the consistently slower induction and recovery with VCEO compared with a reference anesthetic MS-222, a property that constrains its practical use and warrants further dose–response, time-course, and recovery-optimization studies. Therefore, VCEO appears to be a promising anesthetic and sedative alternative, effective and plant-based, without increasing the physiological stress of the animals.