Water Opossum (Yapok)
The Water Opossum (Chironectes minimus), also locally known as the Yapok, is a marsupial of the family Didelphidae. This creature is found in the freshwater streams and lakes in Mexico, Central and South America to Argentina, and is the only living aquatic marsupial. It spends its days in bank-side burrows and emerges after dark to swim and search for fish, crustaceans and other aquatic animals, which it eats on the bank.
True opossums are unique to North America alone. The word “opossum” was taken from the native Algonquian word for the animal. Though the Yapok, as well as other marsupials in South America and Australia are called “possums,” they are not closely related to the Virginia animal, and only derive their name by a generally similar shape and appearance.
The Yapok is a small opossum, 10.6 to 12.8 inches long, with a 14.2 to 15.75 inch long tail. The fur is in a marbled gray and black pattern while the muzzle, eye stripe, and crown are all black. A light band runs across the forehead anterior to the ears, which are rounded and naked. There are sensory facial bristles in tufts above each eye as well as whiskers. The animal’s tail, furred and black at the base, is yellow or white at its end. The hind feet of the Yapok are webbed, while the forefeet (“hands”) are not.
The Water Opossum has several adaptations for its watery lifestyle. It has short, dense fur which is water-repellent. The broad hind feet are webbed and are used for propulsion through water, moving with alternate strokes. They are symmetrical as well, which distributes force equally along both borders of the webbing; this increases the efficiency of the water opossum’s movement through the water. Both males and females have pouches that open to the rear. The female uses her pouch to carry young, even while swimming. A strong ring of muscle makes the pouch watertight, protecting the young.
Yapoks mate in December and a litter of 1-5 young is born 2 weeks later in the nest. By 22 days the offspring are beginning to show some fur, and by 40 days or so their eyes are open, their bodies protruding from the mother’s pouch. At 48 days of age, the young opossums detach from the nipples but still nurse and sleep with the mother.