Anesthesia and transport of juvenile bijupirá Rachycentron canadum
Transport is an important activity in aquaculture, but considered one of the most stressful for fish. Anesthetics are used to reduce stress responses. Thus, the present work aimed to evaluate techniques to improve the transport of juvenile bijupirá, as well as to verify the effectiveness of menthol, MS-222 and eugenol as anesthetics for bijupirá. The techniques used to study transport were the evaluation of different stocking densities (15, 24 and 33 g L-1) using a buffer (1 g NaHCO3 L-1) to maintain the pH, combining different salinities and temperatures (S12 -T19, S30-T19, S12-T23 and S30-T23) and use of the menthol anesthetic (0, 2.5 and 5.5 mg L-1). The anesthetics evaluated for management practices were MS-222 (60, 80, 100 and 120 mg L-1), eugenol (20, 30, 40 and 50 mg L-1) and menthol (35,45 and 55 mg L-1). For transportation experiments, ij 30 g bijupirás were used. In the first transport experiment, the sodium bicarbonate buffer was effective in maintaining the pH of the water above 7 at the different evaluated densities, with mortality (18.2%) occurring only at the density 33 g L-1. In the second transport experiment, the combination of salinity 12 g L-1 (isosmotic point) with temperature 19 ° C was efficient for transport (density: 27 g L-1), as it kept the oxygen concentration high and reduced the stress response. Mortalities occurred only for the combinations S30-T19 (1.2%) and S30-T23 (7.4%). Mortalities in transport experiments were mainly attributed to hypoxia and hypercapnia.The study of menthol in transport used the techniques of previous experiments (1 g NaHCO3 L-1 + S12-T19), although there were no mortality (density: 26 g L-1), menthol was not effective in reducing the responses of stress. Regarding the evaluation of anesthetics, the concentrations 100 mg MS-222 L-1, 30 mg eugenol L-1 and 55 mg menthol L-1 were the lowest to induce anesthesia in juvenile bijupirá (≈ 50 g), but the same efficacy was not reflected in the reduction of secondary stress responses, although after 24 h of anesthesia the fish have already returned to their normal conditions. Thus, buffering the pH together with the use of an isosmotic medium and a temperature of ≈ 19 ° C, are recommended conditions for transporting juvenile bijupirá (≈ 30 g) at a density of up to 27 g L-1. Concentrations 100 mg MS-222 L-1,30 mg eugenol L-1 and 55 mg menthol L-1 were found to be effective in inducing anesthesia in juvenile bijupirá (≈ 50 g). Menthol is not recommended for transporting juvenile bijupirá.