Evaluation of the efficacy of new anesthetic plant extracts and tricaine for juveniles of Tambaqui Colossoma macropomum (Cuvier, 1818): implications for stress responses
The objective of this work was to evaluate the effectiveness of the essential oil (OE) of Nectandra grandiflora Nees, of the extract of Spilanthes acmella var oleracea obtained by extraction technique with supercritical fluid using CO2 and of tricaine (MS-222) as anesthetics for juveniles of tambaqui Colossoma macropomum (Cuvier, 1818), in addition to its effects on physiological parameters and oxidative stress in the post-anesthesia and post-transport periods under sedation. The fish (3.3 to 65.74 g) were acclimated for 15 days in recirculation systems and the water quality parameters were kept within the comfort range for the species. At least five concentrations of S. acmella extract, OE of N. grandiflora and tricaína were tested and the test ranges of concentrations were determined through preliminary tests.The concentration of 20 mg L-1 of S. acmella extract was necessary to promote rapid (induction time <3 min) and deep anesthesia of tambaqui juveniles (46.6 g) that were also evaluated in the post-anesthesia period. secondary stress responses during 72h in recovery. Transient physiological changes occurred mainly between 2 to 24 h after anesthesia with extract of S. acmella, and all physiological variables returned to normal at the end of 72 h in recovery, except for the lower concentrations of Na + blood that remained reduced compared to the reference values.Tricaine was shown to be efficient for rapid and deep anesthesia with concentrations starting at 240 mg L-1 and there were no clear advantages of its use in transport for up to 10 h at the sedation concentration of 20 mg L-1 for stress relief oxidative. The OE of N. grandiflora required a concentration of 200 µL L-1 to determine deep anesthesia, however, it did not determine rapid anesthesia. The extract of S. acmella at a concentration of 10 mg L-1 was sufficient to promote rapid and deep anesthesia of juveniles (3.3 g) submitted to anesthetic baths. After transport for 2, 6 and 10 h in the presence or absence of the N. grandiflora OE and S. acmella extract (30 µL L-1 and 1 mg L-1, respectively) tissues of the juveniles (muscle, liver,brain and gills) were evaluated for oxidative stress responses using the following indicators: total antioxidant capacity (ACAP), GST activity and thiobarbituric acid reactive substances (TBARS). These concentrations of sedation of OE of N. grandiflora and of extract of S. acmella were effective for the transport of this species since they provided protection against oxidative damage mainly in the muscles and gills. Juveniles transported for 2, 6 and 10 h in the presence of S. acmella extract (1 mg L-1) and tricaine (20 mg L-1) did not present significant differences in relation to animals transported without anesthetics as to secondary responses of blood stress, whereas the OE of N.grandiflora at a concentration of 30 mg L-1 attenuated these responses mainly by decreasing or maintaining glycemic levels and maintaining normal blood Na + concentrations. All anesthetics used in this study were effective and safe to promote deep anesthesia with full recovery in tambaqui juveniles. The extracts of the plants S. acmella and N. grandiflora are recommended for the transport of this species in plastic bags for up to 10 h, since there was a relative improvement in secondary stress responses and the lipoperoxidation process in the tissues was reduced in the presence of the extracts .