Abstract
Channa argus breathes air in the following manner: The opercula begin to abduct before the fish breaks the surface.The buccal cavity distends to transport gas from the air-breathing organ into the cavity.Expiration seems to be effected by a hydrostatic head and the contraction of the buccal and pharyngeal cavities, and is done directly into the air.Then the buccal cavity again distends to inspire air. The following abduction of the opercula transports the gas into the air-breathing organ while the branchiostegal membrane prevents the backflow of water.When the fish is breathing bimodally in water, nearly complete renewal of gas occurs at each air breath as evidenced by close agreement between composition of the gas in the air-breathing organ just after inspiration and that of the atmospheric air.When the fish is deprived from water, it violently struggles and repeats air breathing at a markedly higher rate.Ventilation of the air-breathing organ becomes less efficient in this condition, which is illustrated by lower Po2 and higher Pco2 of the gas throughout a breath hold.Our conclusion is that the gas in the organ is replaced by water entering the organ during expiration and then the water is replaced by inspired air when the fish breathes air during bimodal breathing.
