On the mechanism of air ventilaton in anabantoids (Pisces: Teleostei)

Summary

Air ventilation in most Anabantoid species is diphasic, consisting of exhalation and inhalation. Exhalation is the release of air from the accessory breathing organs (suprabranchial chambers) through the mouth either into the water near the surface (e.g.,Ctenopoma) or directly into the atmosphere (e.g.,Osphronemus goramy). Inhalation, i.e., taking in fresh air through the mouth at the surface, immediately follows exhalation. X-ray films show (Figs. 5 and 6) that evacuation of the suprabranchial chambers during exhalation is total or nearly total. This, together with the fact that these chambers can contract at most to a very small extent, led to the conclusion that gas is replaced by water entering the chambers during exhalation and that this water is replaced by fresh air during inhalation. Further analysis of films, including conventional films showing the behavior of the opercular apparatus during air ventilation (Fig. 7), leads to a theory of a double-pumping mechanism responsible for air ventilation. This mechanism consists of the buccal apparatus and the opercular apparatus. It is suggested that both of these structures are able to act as both suction and pressure pumps, and thus air ventilation may be explained as the result of alternating activity of these two pumps.

In the monophasic air ventilation characteristic of (adult)Anabas testudineus, there is no exhalation phase comparable to that of other Anabantoids. Therefore, no water enters the suprabranchial chambers, which remain filled with gas during the whole ventilation process (Fig. 10). Ventilation is limited to one phase comparable to inhalation in other Anabantoids.

The structure of the accessory breathing organs (Fig. 1) and its progressive complication with growth (Fig. 4) were studied inOsphronemus goramy. The arrangement of the labyrinthine plates is in accordance with the requirements of transport of water and gas through the suprabranchial chambers. One plate (the ‘inner plate,’ Fig. 1) separates these chambers into atrium, ventro-caudal, and dorso-caudal compartments, each with its own opening (valve). This organization seems essential for the transport of gas and water through the suprabranchial chambers and ensures that during exhalation, water flows into the chambers from above, so that while water is filling these chambers displaced gas can be sucked through the deep-lying pharyngeal openings into the expanding buccal cavity.