AIR BREATHING
A fish out of water usually dies because its gills collapse, reducing the area of the
respiratory surface, and become dry, effectively stopping the diffusion of oxygen into the
blood. Many fishes, however, have evolved methods of extracting oxygen from air. Such
adaptations permit these fishes to live in oxygen-poor waters, where they come to the
surface to gulp air, or in waters subjected to drying; or they may enable a species to
exploit environments, such as damp beaches, unavailable to other fishes. One method of air
breathing is the development of gills that either secrete mucus or trap moisture that
supports the gills and keeps them wet. Another method is to breathe through a damp skin,
as do the freshwater eels. Very commonly, special chambers have been developed in the
mouth, throat, or head in which inspired air is brought into contact with moist tissues
richly supplied with blood vessels. Some fishes have thin-walled areas in the intestine
where oxygen can be extracted from swallowed air. In still others, the swim bladder, often
mistaken for a lung because of its inflated shape and shiny, silvery white walls, is
modified into an air-breathing apparatus. Air breathing has become so important to some
species that they will drown if not allowed access to air.
Distribution - Anatomy - Circulation -
Respiration
Body Temperature -
Water
Balance -
Swimming -
Gas Bladder
Lateral Line System -
Evolution
- Reproduction