The Giant Amphibian of the River

Mudpuppy (Necturus maculosus)

The mudpuppy is the only wholly aquatic salamander in New England. It is by far the largest salamander found in Massachusetts with adults occasionally reaching total lengths of 15 inches or more.

Larval mudpuppy, note the stripes.

Most of the amphibians have an aquatic larval stage, then metamorphose and enter a terrestrial juvenile/adult stage. Most amphibians lay their eggs in water. The eggs hatch and the predaceous larvae swim around feeding on small invertebrates. Larval salamanders are well adapted for an aquatic existence. They have large feathery, external gills at the back of their heads. The gills have an enormous surface area which allows direct respiratory exchange between the larvae and the surrounding water. Larval salamanders also have an enlarged, fleshy fin along the dorsal and ventral surfaces of their tail that enables them to swim more efficiently.

Depending on the species, the larval phase of development may last from a few weeks to 2-3 years. Most species of salamanders undergo a radical metamorphosis at the end of the larval period and transform into terrestrial juveniles, i.e. smaller versions of the adult stage.

During metamorphosis larval salamanders undergo many anatomical and physiological changes. They absorb their big bushy gills. Such large highly vascularized organs would be impossible to keep moist on land and could be easily damaged in a terrestrial organism. The large fleshy fin folds on their tails that propelled the larvae through the water provide no benefit on land and are resorbed.

Larval mudpuppies, like all other aquatic salamander larvae, have large bushy gills and a large fin fold on their tail fin. They are brownish in color and have very distinct light stripes which extend from near the tip of their nose to the tip of their tail.

Larval mudpuppy, note the stripes.

Mudpuppies retain this larval appearance for three years. Mudpuppies are paedomorphic; they undergo a partial metamorphosis and retain some juvenile characteristics as adults. Unlike any other Massachusetts' salamander, mudpuppies never lose their gills. In an aquatic environment external gills are more efficient at exchanging gases than are internal lungs so selective pressures have favored those animals that retained their gills through metamorphosis. Curiously, mudpuppies have lungs but they use them to maintain buoyancy in the water much as a fish uses its swim bladder. Mudpuppies never lose the large fleshy fins on their tail either. Since the adults are aquatic, this large fleshy fin fold enables them to swim more efficiently. About the only obvious change in an adult mudpuppy is the loss of their larval stripes; their color is a uniform brown with blue-black spots.

Adult mudpuppy, approximate length 15 inches; note the extended gills behind the head, just in front of the legs.

It is believed that adult mudpuppies do not occupy the same habitat throughout the year but undertake migrations during the breeding season. Adults may migrate into shallow streams or the shallows of lakes where they form small breeding aggregations or congresses in the late fall. In the Connecticut River egg laying probably occurs around the first or second week of June, although the exact time is temperature dependent. The female attaches her 48-128 eggs individually to the bottom of a submerged flat rock or other structure. Eggs take around 40 days to hatch.

For inquiries concerning amphibians and reptiles, contact Alan Richmond, Biology Department, Box 5810, Morrill Science Center, University of Massachusetts, Amherst, MA 01003-5810