Water Oxygen Content Affects Distribution of T and B Lymphocytes in Lymphoid Tissues of Farmed Sea Bass (Dicentrarchus Labrax)

Intensive aquaculture systems have stimulated proper management in order to limit stressful stocking conditions and environmental impact. This should improve fish wellness and counteract adverse water characteristics such as high concentrations of carbon. The oxygen can be considered a key factor since critical conditions leading to chronic rise of blood catecholamines can depress the number and Oxygen-carrying capacity of erythrocytes. In this research, we evaluated the effects of variation in water oxygen (from 6 +/- 1 to 13 +/- 1 mg/L) on lymphocytes density in sea bass by using flow cytometry and immunohistochemistry. Gut, gill, and thymus T-cells were significantly enhanced in percentage in hyperoxygenated fish compared with normo-oxygenated group, while Peripheral Blood Leukocytes (PBL), head kidney, and spleen T-cells were not significantly different. Contrarily, in PBL, head kidney and spleen hyper-oxygenation treatment provoked an enhancement of B lymphocyte percentages. The distribution of positive T-cells in hyper-oxygenated fish varied in the organs and followed the relative increments/decrements observed in flow cytometry. This study remarks the sensitivity of sea bass adaptive immunocytes to oxygen concentration, evidenced by the modification of parameters. Sea bass culture under high-flow water recycling and at around 12-13 mg/L oxygen concentrations is therefore suggested to enhance the immune response capacity.