Breathing and function of the spiracles in Polypterus senegalus

Abstract

Summary Polypterus frequently visits the surface of the water and gives out a bubble of gas from beneath the operculum. At the same time the spiracles open for a fraction of a second. In the first experiment, fish were put in ordinary tap water without aeration but allowed access to the surface. In the second experiment, the fish were put in aerated water and allowed access to the surface. In the third experiment, fish were put in water and access to the surface was prevented by an iron mesh which was submerged 2 in. under the surface of the water. In the fourth experiment, fish were put in aerated water, also with no access to the surface. In the first and second experiments respiratory movements increased before the fish came to the surface followed by a decrease when the fish went to the bottom again. The rate of surfacing increased with the activity of the fish. An active fish in aerated water surfaced more frequently than an inactive fish in non-aerated water. In the third experiment, after introducing the iron mesh, the number of respiratory movements gradually increased, reaching a maximum after which they decreased and the fish died. In the fourth experiment, in spite of the iron mesh, the fish survived but under high respiratory tension. It is concluded that the spiracles in Polypterus are used to inhale air either under conditions of low oxygen concentration or during periods of high activity.