Evaluation of stress in the transport of juvenile Cobia Rachycentron canadum
The present study evaluated the use of the anesthetic benzocaine and the stress response in the transport of juvenile bijupira Rachycentron canadum. To determine the optimal concentration, the fish (9.4 g) were exposed to 30, 50 and 70 mg L-1 of benzocaine. To assess blood parameters and oxidative stress, fish (16 g) were exposed to the same concentrations as before. For 30 mg L-1 of benzocaine, the fish exceeded 10 min to reach the last stage of anesthesia, whereas for 50 and 70 mg L-1 this time was up to 3 min. For recovery, fish exposed between 30 and 50 mg L-1 returned within 3 min, while those exposed to 70 mg L-1 exceeded 10 min. For carbonyl protein and TBARS, the highest values were found in the liver, where the concentration of 30 mg L-1 showed the highest levels (P <0,05) for carbonyl protein and 50 and 70 mg L-1 showed the highest levels (P <0.05) for TBARS. Also in the liver tissue, the highest and lowest values (P <0.05) of GST and GSH were found simultaneously, respectively. Two transport experiments were also carried out (8 h). The fish were packed in polyethylene bags and packed in styrofoam boxes. In the first experiment, two concentrations of benzocaine (2 and 6 mg L-1) and an anesthetic-free treatment were evaluated. To evaluate the hematological parameters, blood samples were collected from fish (30.9 g) before transport (control), 0, 2, 24 and 48 h after transport. In the second experiment, the fish (37.5 g) were packaged at densities of 10,20 and 30 g L-1 and hematological parameters were measured before transport (control), 0, 2 and 24 h after transport. For both experiments, water samples were collected to measure pH and concentrations of dissolved oxygen, ammonia and CO2. No mortality was observed in the experiment with addition of benzocaine. At 0 h, blood glucose was higher for 6 mg L-1 (P <0.05) of benzocaine, although in 48 h it had already returned to values similar to the control. Mortality of 39.5% of fish was observed at a density of 30 g L-1. The CO2 concentration was significantly higher (P <0.05) at a density of 30 g L-1. Blood glucose at a density of 30 g L-1 was higher (P <0.05) than in other treatments, returning to values close to the control only for 20 and 30 g L-1 after 24 h.The results suggest that for juvenile bijupirá: i) the ideal concentration of benzocaine for their anesthesia is 50 mg L-1; ii) there is no advantage in the use of benzocaine in its transportation; and iii) must not be transported for 8 h at densities greater than 20 g L-1.