Toxicity and gill alterations in Astyanax lacustris exposed to Lippia alba essential oil

Essential oils are recognized as sedatives and anesthetics in fish; however, their toxicity at varying doses needs further evaluation to ensure safe use. This study assessed the toxic effects of the essential oil from Lippia alba (EOLA) on yellow-tail lambari (Astyanax lacustris) juveniles through an acute toxicity test over 96 h. The fish were exposed to different concentrations of EOLA (5, 10, 15, and 20 mg·L^-1), along with two control groups (one with alcohol and one without). We analyzed several parameters, including water quality, behavior, mortality rates, and histological alterations in the gills. Mortality was observed only at a concentration of 20 mg L^-1, with a rate of 42.85%. The lethal concentration (LC50) based on the concentrations tested. Histological examinations revealed that progressive gill lesions were correlated with increasing concentrations, with epithelial hyperplasia being the most common alteration. The fish exposed to EOLA exhibited agitated swimming, increased opercular movement, and excessive mucus secretion, particularly at 10 mg L^-1 or higher concentrations. Despite these behavioral responses, water quality remained within acceptable levels. Overall, the results suggest that EOLA may be safe for A. lacustris when exposure is limited to less than 24 h without compromising their survival or causing significant damage to their gills.