How Does a Lungfish Breathe?

It's all in the name. Lungfish are a rare, snake-like species of fish that actually breathe air through their lungs in much the same way we do. The origin of this freshwater fish dates back to the Devonian period -- its primitive bony skeleton and ability to breathe air serve as reminders of a bygone era from which many species did not emerge as unchanged as the lungfish.

  1. Origin

    • The existence of lungfish has been traced back millions of years. Over that time, many different species of lungfish have died out. Only six species exist today, which are divided into two families: the Lepidosirenidae, found in South America and Africa, and the Ceratodidae, found in Australia. The Lepidosirenidae family has two lungs, while the Ceratodidae has only one.

    Lungs

    • It's important that the lungfish have two lungs in the extremely dry conditions of Africa and South America because during periods of drought, the lungfish must survive in mud with no hope of water for several months. The lungfish can get away with one lung in Australia because even during the worst dry spells, there will likely be at least a puddle of water. A lungfish's lungs work through gas exchange (as in humans) and are composed of complex internal air sacs that increase the surface area for gas exchange. When in the water, the lungfish breaks the surface to inhale air through two small nostrils on the tip of its snout.

    Gills

    • Of all the lungfish, the Australian species is the only one with the ability to respire through its gills. The fish can decide when it's best to gather oxygen from the air or underwater. When its gills are in use, the circulatory system of the lungfish function similarly to a typical fish. In all lungfish other than the Australian species, there are a set of gills present. These are basically useless because they've atrophied, hence the need for two lungs instead of one.

    Meaning

    • It seems rather counterintuitive that a fish needs air to breathe. The principles of evolution, though, allow us to understand why the lungs of these fish have not evolved away and become strictly gills. Because of the dry and drought-prone climate lungfish inhabit, they're better off breathing air, as water shortages are common in these areas and could surely kill them were it not for their ability to breathe outside of water. When a water shortage occurs, the lungfish covers its body in a protective secretion and lies dormant in mud (or lies in what meager water supply it can find), all the while breathing air.