Abstract
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.
Highlights
The European sea bass, Dicentrarchus labrax (L.), is a highly cultured fish species in Mediterranean mariculture [1,2], which had a decisive impulse from the rapid decline of natural fisheries stocks
Water oxygen levels below 6 mg/L can be stressful for sea bass, while levels below 2.85 mg/L can be lethal for all fishes [9]
DLT15+ cells were observed in thymus, gut, and gills compared with spleen, head kidney, and blood
Summary
The European sea bass, Dicentrarchus labrax (L.), is a highly cultured fish species in Mediterranean mariculture [1,2], which had a decisive impulse from the rapid decline of natural fisheries stocks. Hypoxia and hypercapnia, generated during fish maintenance, can influence the adrenal reaction as an “adaptive-syndrome” by raising stress hormones cortisol and catecholamines [4,5,6]. It can delay larval development [7] and could provoke fish death, depressing severely the metabolism of brain and skeletal muscles [8]. The serum content immunoglobulins shown (lymphocytes, granulocytes, and macrophages) scattered in the mucosa, with a prevalence of to be higher in sea bass reared in hyper-oxygenated water [14]. 2. Results groups the highly significant predominance of T lymphocytes compared with Ig‐positive cells (4.2 and 2.9 times more numerous in HO and NO, respectively). A rise of T cells (+75%) was found in the
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