Hydrolate toxicity of Lippia alba (Mill.) N. E. Brown (Verbenaceae) in juvenile tambaqui (Colossoma macropomum) and its potential anaesthetic properties

The study aimed to establish the lethal concentration at 96 h (LC50-96h) of hydrolate of Lippia alba (citral chemotype) (LAH) in juvenile tambaqui (Colossoma macropomum), as well as to identify the anaesthetic induction and recovery times. The acute toxicity test LC50-96h was performed in five animals per replicate (three replicates per treatment). The concentrations tested were 5, 6, 7 and 8% hydrolate diluted in water, and a control treatment containing only water. During the LC(50-96h )test, the physical and chemical parameters of the water were evaluated (temperature, dissolved oxygen, pH, and electrical conductivity). Water was also collected at the beginning and end of the experiment for the analysis of alkalinity, hardness, total ammonia, Na+, K+ and Cl- levels. Gills were collected from the survival fish to determine the density of gill mucous cells (DGMC). The concentrations of 10, 15, 20 and 25% of the hydrolate diluted in water were used for anaesthesia tests, which lasted up to 30 min (15 animals/treatment). After anaesthesia, the recovery time was evaluated. The toxicity test indicated LC50-96h 7.43% (confidence interval: 6.9-8.2%). During LC50-96h , ion loss and increased mucous gill cell density was observed in treatments with LAH. However, a long exposure time (up to 96 h) at lower concentrations (6, 7 and 8%) of the by-product caused osmoregulatory (ion loss) and cellular (increased DGMC) disturbances. The data also indicated that increasing the concentration of hydrolate proportionally decreases the time for anaesthesia induction. Anaesthesia recovery time was not significantly affected by LAH concentration. The concentrations of 20 and 25% of LAH showed the best times for anaesthesia induction in juvenile tambaqui (1.76 min and 2.01 min, respectively).