Physiological Stress Response and Oxidative Status in Tambaqui () Fed Diets Supplemented with Selenium.

The present study aimed to evaluate the physiological responses to transport stress in juvenile tambaqui () fed a diet supplemented with hydroxy-selenomethionine (OH-SeMet; Selisseo, Adisseo) and determine through stress biomarkers whether selenium supplementation could reduce the impact of transport stress on tambaqui resilience. Juvenile fish (15.71 ± 1.90 g) were randomly distributed into five experimental groups; one fed a basal diet without inclusion of OH-SeMet (0.0 mg Se/kg) and four other groups fed supplemented diets with selenium in the form of OH-SeMet at concentrations of 0.3, 0.6, 0.9, and 1.2 mg Se/kg over 75 days. After this period, the fish were transported for 4 h in plastic bags (60 L), and sampling took place before transport (baseline), immediately after transport, and 24 h later. The effects of dietary OH-SeMet in tambaqui challenged by transport were studied in terms of antioxidative status (superoxide dismutase, catalase, glutathione peroxidase, glutathione s-transferase, and reduced glutathione); stress markers (serum cortisol, blood glucose, ionic and hematological parameters), and immunological status (respiratory burst activity and total protein, A/G ratio). Following transport, we observed an elevation in cortisol and blood glucose concentrations, accompanied by hemoconcentration, as evidenced by elevated hematocrit, erythrocyte count, hemoglobin concentration, and mean corpuscular hemoglobin concentration (MCHC). Additionally, there was a decrease in immune response, indicated by reduced respiratory activity of leukocytes and an osmotic imbalance, which culminated in hypochloremia, increased plasma protein concentration, and a rise in red blood cell volume, all of which were measured 24 h after the stressor was applied. Twenty-four hours after transport, the antioxidant defense system was activated, and no recovery of homeostasis was observed for most of the parameters analyzed. The dietary inclusion of selenium did not alleviate the hormonal, metabolic, hematological, and ionic changes caused by transport, but at a concentration of 0.9 mg Se/kg, it was able to increase the activity of enzymes related to oxidative stress (catalase and superoxide dismutase, mainly) in tambaqui juveniles submitted to this challenge.