Stingray, Freshwater


Potamotrygonidae sp.


Adult length: vary in size from 10 to 12 inches across and approximately 3 feet long.  Appearance: flat-bodied with five ventral slot-like body openings called gill slits, upper surface is covered with denticles (sharp tooth-like scales), eyes and spiracles are located on top of the head, ventrally located mouth. Most species are brownish or grayish and often have distinctive spotted or mottled patterns, but a few species are largely blackish with contrasting white spots.

Family

Potamotrygonidae

Order

Myliobatiformes

Class

Chondrichthyes

Range

South America

Habitat

Freshwater river systems - calm waters, especially the sandy edges of lagoons, brooks and streams

Life Expectancy

Sexual Maturity

About 3 years

Diet

In the wild, juveniles initially feed on plankton and adults eat small mollusks, crustaceans and the larvae of aquatic insects and catfish; in the Zoo, they are fed a scientifically developed, commercially available diet and chopped fish.

Status

IUCN – Data Deficient

Behaviors

Stingrays are generally non-aggressive and intelligent creatures. They are often found lying still, buried in the sandy sediment at the bottom of a stream, particularly during the warmest part of the day. Females produce eggs, but these develop inside the female. The young hatch inside the female and are then ‘born’ live after a gestation period of no more than three months. The litter size varies massively, from 3 to 21 young.

Adaptions

Freshwater stingrays have a venomous caudal barb, and are one of the most feared freshwater fishes in the Neotropical region. The stingray’s venom apparatus is composed of the tail, or caudal appendage, along with a barbed spine and its enveloping integumentary sheath, and associated venom glands. There is a wedge-shaped area of tissue that is in close contact with the spine; thus, when the spine is lying flat against the dorsal surface of the ray, it is bathed in a mélange of venom and mucus. All stingray venoms are very similar. They contain serotonin, 5-nucleotidase, and phosphodiesterase. The latter two enzymes are responsible for the necrosis and tissue breakdown seen in stingray envenomations; serotonin is the cause of inexorable pain in the region of the injury. These actions will continue unabated if left untreated. Most batoids have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such as snails, clams, oysters, crustaceans, and some fish.

Special Interests

The genus name, Potamotrygon, is from the Greek potamos that means ‘river’ and trygon, which means ‘three angles’, and may refer to its body shape. It is said that the natives of South America fear the stingray more than they do the piranha. River stingrays are the only family of batoids completely restricted to freshwater habitats. There is a great deal of confusion concerning the terms sting, spine, and barb. The sting properly refers to the entire structure: the spine, its sheath, and the venom glands. The term spine properly refers to the rigid surface of the sting, which is made of dentin. The barbs are the backwards facing serrations associated with the lateral aspect of the spine. Depending on species, one or more spines may be present on the dorsal surface of the tail. The barbs facilitate the tearing of the ray’s integumentary sheath and the broadening of the victim’s wound. Barbs also work like a backwards pointing fish hook and make disengagement more time consuming and traumatic. Since the serotonin in stingray venoms produces severe and immediate onset of local pain, any sting that is relatively free of pain indicates that no actual envenomation occurred and the “lucky” victim endured a “dry” sting. This may be due to one or more of several reasons: the sheath was previously ruptured, releasing its venom store; the sheath failed to penetrate the wound; the sheath failed to rupture, so the venom remained contained; or, the spine had been broken off previously. For those who receive a dose of venom along with the physical trauma of being hit, the tissue necrosis and subsequent secondary bacterial infection that occurs is extremely difficult to treat; and many months and several courses of intravenous antibiotics may be necessary.

Folklore

Conservation

Jacksonville Zoo History

Freshwater Stingrays first arrived at the Jacksonville Zoo and Gardens in 2008. So far we have had three types: some subspecies crosses to test the waters; Orange-Spotted Freshwater Stingray (Potamotrygon motoro); and a Pearl Freshwater Stingray which is a stingray still waiting for its appropriate taxonomic classification.

Exhibit

Range of the Jaguar