Smithsonian National Zoological Park l Friends of the National Zoo



Rays of Interest

Freshwater Stingrays at the Smithsonian's National Zoo

The Flooded Forest in the Zoo's Amazonia exhibit has seen a lot of success with freshwater stingrays since the Zoo obtained its first four freshwater rays in 2001. A pair of Potamotrygon castexi have produced 28 pups. Six rays were donated to the Tennessee Aquarium, and the new pair and another female will be donated to the South Carolina Aquarium.

Stingrays have an interesting mode of reproduction. Following fertilization, embryos are first nourished by yolk from the egg, then the yolk's nourishment is supplemented by a kind of milk produced in the mother's uterus. The young are often born with an intact yolk sack, which is absorbed in two to three days.

Also known as river stingrays, these animals are native to South America. Stingrays are members of the elasmobranch subclass, a group of fish that includes sharks, skates, and sawfish. Despite appearances, they do have scales, which are known as dermal denticles or placoid scales, and give many of these fishes the texture of sandpaper.