The Influence of Gas Gland Metabolism and Blood Flow on Gas Deposition into the Swimbladder of the European Eel Anguilla Anguilla

The effects of blood flow through, and metabolic activity in, the swimbladder epithelium on gas deposition into the swimbladder have been analysed in the European eel, Anguilla anguilla. Blood flow in the artery supplying the retia was measured by Doppler flow probes; measurement of O2 and CO2 content in arterial and venous blood samples from the swimbladder allowed calculation of the rates of O2 removal from, and CO2 addition to, swimbladder blood. 83 % of the O2 removed from the blood was transferred into the swimbladder lumen and only 17 % was metabolized in the tissue. In spite of the deposition of CO2 into the swimbladder lumen, the CO2 content in rete venous blood was higher than that in arterial blood, indicating production of CO2 in the swimbladder tissue. The respiratory exchange ratio, calculated from O2 consumption and CO2 production of the swimbladder tissue, was significantly greater than one. Gas deposition into the swimbladder increased with increasing swimbladder arteriovenous pH difference, indicating acid release from gas gland cells, and thus their metabolic activity. The rate of gas deposition into the swimbladder increased with increasing blood perfusion of the swimbladder tissue. Under hypoxic conditions, gas deposition was significantly reduced, as was blood flow through the swimbladder tissue. The decrease in gas deposition during hypoxia coincided with a reduction in the swimbladder arteriovenous pH difference. The results therefore demonstrate that the rate of gas deposition is dependent on blood perfusion of the swimbladder tissue and on metabolic activity of the swimbladder tissue, both of which are reduced under hypoxic conditions.