Why an Axolotl Waves Its Gills

An axolotl looks as if it wears six tiny feather dusters beside its head. These are external gills, meaning they grow outside its body. This salamander lives in water throughout its life. Wild axolotls live in canals near Mexico City. Their gills help them take in the oxygen their bodies need.

Water contains dissolved oxygen. This oxygen is mixed into the water and cannot be seen. It is not the same as a bubble of air. Like other animals, an axolotl needs oxygen to help its body use food for energy. Gills allow it to collect oxygen without coming to the surface for every breath.

A heading for a close look at these gills could be “A Large Surface in a Small Space.” Each gill stalk has many thin branches called filaments. These give the gills much more surface area than smooth stalks would have. More surface area means more space where oxygen can pass from the water into the animal.

Inside the filaments are tiny blood vessels, tubes that carry blood. Oxygen passes through the thin outer covering of the gills and enters the blood. The blood then carries oxygen around the body. A drawing showing arrows from the water into a filament could have this caption: “Oxygen moves from the water into the blood.”

There is a problem, though. As oxygen enters the gills, the water right beside them has less oxygen left. An axolotl can flick its gills backward. This movement brings different water past the filaments. With that nearby water refreshed, more oxygen is available. Moving through the water can also help bring new water past the gills.

The gills are not an axolotl’s only way to get oxygen. Oxygen can also pass through its skin, and it can gulp air into its lungs at the surface. Still, those feathery branches do important work underwater. They are useful breathing parts, not decorations!