The Active Transport of Oxygen and Carbon Dioxide into the Swim-Bladder of Fish

I N T R O D U C T I O N During the experiments with their bathyscaphe P6r£s, Picard, and Ruivo (1958) at a depth of 2200 m observed fishes (Halosaurus johnsonii) which floated. These fishes have therefore the same density as the surrounding water. T h e density of a fish without a gas-filled swim-bladder is practically independent of depth and it is a few percent higher than the density of the surrounding water (Denton and Marshall, 1958). A fish with a gas-filled and closed bladder, however, is as a Cartesian diver at a depth in an unstable equilibrium of floating. According to Borelli (1679) fishes should control the volume of the swim-bladder by muscular activity. But this view is in contrast to several experimental findings (Moreau, 1876; Jacobs, 1930, 1932, 1940). Morphological studies (Jaeger, 1903; Marshall, 1960) showed that the rete mirabile (Delaroche, 1809; Woodland, 1911;Krogh, 1922; Scholander, 1954; Wittenberg et al., 1964), the gas gland (Muller, 1840), and the oval (Winterstein, 1921; Ledebur, 1929) of the bladder are organs which may be involved in the secretion (Bohr, 1894; Jacobs, 1932) and the resorption (Moreau,