Intestinal respiration is an auxiliary respiration in the finch and puffer, some catfish and carp fish, which ingest air from the water surface and pass it through the intestines. Blood oxygenation takes place in certain parts of the intestine, which has clusters of blood capillaries in its walls.

Doras and Callichthys have so well developed intestinal respiration, which is their main respiration, that if these fish are kept in water, but do not give them the opportunity to rise to the surface and take in air, they die in about 2 hours. But if kept in moist air, they live for several hours.

The finch rises to the surface of the water to ingest air at: t= 10° 2-3 times per hour, and at 25-30° already 19 times. If the water is boiled, i.e., reduce P02, the finch rises to the surface at t = 25-2.7°' once an hour. At t=5° in running water it did not rise to the surface for 8 hours. In these experiments it is clearly enough shown that intestinal respiration, which is an addition to gill respiration, quite satisfactorily copes with its function at low demands of the organism in 02 (at t = 5 °) or at high concentration of oxygen in the environment .(running water). But gill respiration is not enough, if the exchange in the body is increased (t  = 25-30 °) or strongly reduced P02 in the environment (boiled water). In this case, intestinal respiration is additionally activated, and the finch receives the required amount of oxygen.