Oxygenation of European seabass (Dicentrarchus labrax L.) in cages through aeration and effect on lipid metabolism

Two groups of the same batch of European seabass were used in an industrial-scale trial in sea cages in Vorios Evoikos, Greece. For about one month, one of the two cages was oxygenated by use of compressed air injected in seawater through an AirX frame (Oxyvision A/S, Norway) at 3.5 m depth, while oxygen concentration and temperature were monitored every 30 min. The liver, gut, and pyloric ceca samples were taken from fish of both groups for measurement of gene expression of phospholipase A2 (PLA2) and hormone-sensitive lipase (HSL), and for histological analysis at the middle and end of the experiment. Real-time qPCR was performed with housekeeping genes ACTb, L17, and EF1a. The expression of PLA2 increased in pyloric caeca samples from the oxygenated cage, suggesting that aeration improved the absorption rate of dietary phospholipids (p < 0.05). Expression of HSL increased significantly in liver samples from the control cage, in comparison with the aerated cage (p < 0.05). Histological examination of sea bass samples revealed an increased fat accumulation in the hepatocytes of fish in the oxygenated cage. The results of the present study showed increased lipolysis induced by low DO levels in farmed sea bass in cages.