The Secretion of Oxygen into the Swim-bladder of Fish I. The transport of molecular oxygen

Fish were maintained in sea water equilibrated with a gas mixture containing a non-equilibrium mixture of the three molecular species of oxygen, O18-O 18 (mass 36), O18-O t6 (mass 34), and Ole-O 16 (mass 32). Analyses in the mass spectrometer, of the gases secreted into the swim-bladder showed that no change in the relative abundance of these three molecular species had occurred during the secretory process and that therefore no exchange of atoms between oxygen molecules had occurred. Scission of the oxygen-oxygen bond probably does not occur during the transport process. It is concluded that the active transport of oxygen into the swim-bladder by the gas gland is a transport of molecular oxygen. Gases are brought into the swim-bladder of fishes through the combined action of a glandular epithelium, the gas gland, and a vascular structure, the rete mirabile, supplying blood to the gland. Oxygen constitutes the major portion, up to 95 per cent, of the gas mixture elaborated by the gland and is the substance transported. The partial pressure of oxygen in the swimbladders of fish living at great pressures in the depths of the sea may exceed 150 atmospheres (Blot, 1807; Richard, 1895; Schloesing and Richard, 1896; Scholander and van Dam, 1953). The partial pressure of oxygen in the swimbladder of these fish is commonly 500-fold or in one case, 10,000-fold (Kanwisher and Ebeling, 1957) greater than the partial pressure of oxygen in the ambient sea water. Biot (1807), the discoverer of the phenomenon, stated that these pressure differences were achieved by active secretion of oxygen. Nitrogen and argon, although constituting only a small proportion of the total gases may also be present at partial pressures far greater than the ambient. They are brought into the swim-bladder by a physical mechanism (Wittenberg, 1958) which is a corollary of oxygen secretion.