Mudpuppies never lose their gills as they mature. Even though they have lungs mudpuppies spend their entire lives underwater. The adult gills resemble fish gills in many ways. The bright red exposed gills are often found closed against the body in cool, highly oxygenated water.  In warmer, poorly oxygenated water, the gills expand to increase water circulation and provide a greater surface area for oxygen intake. Mudpuppies also absorb oxygen through their skin and by occasionally breathing air at the surface.

Other distinguishing features of mudpuppies, as compared with other salamanders, are the absence of eyelids and of an upper jaw. They show a degree of parental care, tending to the eggs after attaching them to submerged stones and logs.

Mudpuppies prefer shallow lakes and streams that have slow-moving water and rocks to hide under but have been found in up to 90 feet of water.  The mudpuppy diet consists of small fish and many invertebrates, including crayfish, snails, and worms. Mudpuppies mature at four to six years and can live to be more than twenty years old.