Amphibians
Mudpuppy
Necturus maculosus · also called mudpuppy, waterdog, common mudpuppy
The mudpuppy is a large, permanently aquatic salamander of North American lakes and rivers, instantly recognisable by the maroon feather-dusters of gills flaring from each side of its neck. It never grows out of its larval body, never comes onto land, and can spend two decades in the same river.
Overview
Mudpuppies live in permanent fresh water — lakes, rivers, and big streams — across eastern North America, from Canada down through the Great Lakes and Mississippi drainage to the southeast. They favour water with plenty of cover: flat rocks, logs, undercut banks, and weed beds, where they shelter by day and emerge at night to hunt. They are active year-round, including under winter ice.
Gills for life
Most salamanders hatch with gills and lose them at metamorphosis. The mudpuppy keeps its external gills permanently — a condition called paedomorphosis — and never transforms for land. The gills are its main way of breathing, and it tunes them to the water: long, bushy, and blood-red in warm, still, low-oxygen conditions; short and stubby in cold, fast, oxygen-rich water. It also has only four toes on each foot, where most salamanders have five on the hind feet.
Hunting
Mudpuppies are nocturnal carnivores that eat crayfish, aquatic insects, worms, snails, small fish, and fish eggs, locating prey by smell and by water movement in the dark. They are slow but persistent foragers.
The folklore
Few animals attract as much false belief. Mudpuppies are said to bark, to be venomous, to be poisonous to eat, and to spoil fishing — none of which is true. They are entirely harmless. An angler who hooks one should unhook it and let it go.
An indicator species
Because a mudpuppy spends its whole life in one place, breathes through bare gills and skin, and lives a long time, it is very sensitive to pollution, silt, and low oxygen, and biologists use its presence or absence as a gauge of water health. It is also the sole host of the larvae of the mudpuppy mussel, tying the fates of the two species together.
Status
The mudpuppy is Least Concern and still widespread, but it is secretive and hard to survey, and local populations decline where water is degraded or where the salamandrid-killing details of pollution and dams take hold.
Mudpuppy: common questions
Why does the mudpuppy keep its gills its whole life?
The mudpuppy is paedomorphic — it becomes sexually mature and reaches full size while keeping larval features, most obviously the external gills, and it never undergoes the metamorphosis that would let it live on land. This is a fixed, inherited condition for the whole species, unlike the axolotl (which is normally paedomorphic but can sometimes be forced to transform) or the tiger salamander (which usually transforms but sometimes does not). Staying in the water full-time works well in the stable, permanent lakes and rivers the mudpuppy lives in.
Do the gills change size?
Yes, quite visibly. The gills are how the mudpuppy breathes, and it adjusts them to the water it is in. In warm, stagnant, oxygen-poor water the gills grow long, bushy, and bright red as blood flow increases to extract every bit of oxygen. In cold, fast-flowing, well-oxygenated water the same animal's gills become short and stubby because less surface area is needed. A mudpuppy will also fan its gills with a rippling motion to move fresh water over them.
Is a mudpuppy dangerous or poisonous?
No. Mudpuppies are the subject of a lot of false folklore — that they bark like a dog (they can make a faint squeak at most), that their bite is venomous, that they are poisonous to eat, or that their presence ruins fishing. None of this is true. They are harmless, non-venomous, and non-toxic. Anglers who hook one while fishing for other species should simply unhook it gently and return it to the water; historically many were killed on the mistaken belief that they were harmful.
Why do mudpuppies matter for water quality?
Because they live their entire lives in one stretch of water, breathe through exposed gills and permeable skin, and are long-lived, mudpuppies accumulate whatever is in their environment and are sensitive to pollution, siltation, and low oxygen. Declines or disappearances of mudpuppies are treated by biologists as an early warning about the health of a lake or river. They are also the primary host of the mudpuppy mussel, a freshwater mussel whose larvae can develop only on mudpuppy gills, so losing the salamander means losing the mussel too.