In complex animals, where the cells of internal organs are distant from the external environment, respiratory systems facilitate the passage of gases to and from internal tissues. In such systems, when there is a difference in pressure of a particular gas on opposite sides of a membrane, the ...
The process involves simple diffusion across gas-exchange organs like gills, skin, and air-breathing structures. Air-breathing species have evolved specialized mechanisms for extracting oxygen from the air in variable water levels. The adaptability of fish respiratory systems arises from diverse habitats...
Air-breathing fishes have evolved a variety of air-breathing organs (ABOs) for obtaining oxygen from above the water surface but retain gills, ventilated by cranial muscles, for the uptake of a variable proportion of their oxygen requirements, dependent on species and conditions, and for excretion...