Stingray Species and Groups: Ribbtontail, Six-Gill, Freshwater and Round Rays | Sea Life, Islands and Oceania

Home | Category: Rays

STINGRAY SPECIES

white-blotched river stingray

Stingrays belong to the family Dasyatidae. They are cartilaginous fish related to sharks. There are about 220 known stingray species organized into 29 genera and eight families: 1) sixgill stingrays (Hexatrygonidae); 2) deepwater stingrays (Plesiobatidae); 3) stingarees (Urolophidae), 4) round stingrays (Urotrygonidae), 5) whiptail stingrays (Dasyatidae), 6) river stingrays (Potamotrygonidae), 7) butterfly rays (Gymnuridae) and 8) eagle rays (Myliobatidae). Many sources list stingarees and round stingrays together as Urolophidae., [Source: Wikipedia]

There are many species of rays. These include stingrays, electric rays, manta rays, butterfly rays, and round rays. Sawfish and guitarfish are also classified as rays. Not all of these rays have stingers and not all rays sting.

Some stringrays such as the thorntail stingray (Dasyatis thetidis), are found in warmer temperate oceans. Other such as the deepwater stingray (Plesiobatis daviesi), are found in the deep ocean. River stingrays and a number of whiptail stingrays (such as the Niger stingray (Fontitrygon garouaensis)) are found in fresh water. Most spend most of their time near the sea floor but some, such as the pelagic stingray and the eagle rays, are pelagic.

Television adventurer Steve Irwin was killed by a short-tail stingray (Dasyatis brevicaudata), a huge but normally docile fish also known as a smooth stingray or bull ray. The largest of all stingrays, it can grow up to 4.3 meters (14 feet) long and weigh more than 340 kilograms (750 pounds). Short-tail stingrays possess two tail spines: “a slender spike in front of a huge jagged bayonet.” The ray that injured Irwin plunged its rear tail barb, reportedly close to 20 centimeters (eight inches) long, into his chest. [Source: Adam T. Hadhazy, Scienceline September 11, 2006]

Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Freshwater Stingrays

Freshwater stingrays live in the Amazon basin. Many feed on insects and break down their tough exoskeletons with mammal-like chewing motions. These creatures are more feared than piranhas because the injury is more painful and slower to heal than a piranha bite. Because parasites found on freshwater stingrays are more similar to those found in the Pacific than the Atlantic, scientists have deduced that 50 million years ago, before the Andes rose, the Amazon flowed into the Pacific. Swimming in the Amazon is generally okay. But the first basic rule is shuffle your feet in shallow water to avoid stepping on a stingray.

The stingray subfamily Potamotrygoninae lives only in fresh water, sometimes found more than 1600 kilometers away from the ocean. They lie buried in sand or mud in backwaters and shallows of rivers. Members of this group only occur in West Africa and the Atlantic drainages of South America. They do not appear in all South American Atlantic-draining river systems, however, and some, like Potamotrygon leopoldi, are only found in a single river. Their restricted habitat renders the group vulnerable to human activities). Freshwater stingrays in Africa, Asia and Australia are in another family, Dasyatidae.

Stingrays of the subfamily Potamotrygonidae (river stingrays) tend to be smaller, usually less than 30 centimeters in diameter and less than one meter long, although a few may attain two meters. A unique aspect of river stingrays is their chemical adaptation to fresh water; their blood contains very low concentrations of urea, and their rectal gland (used by fishes for salt secretion) is reduced. Some male river stingrays have more prominent cusps on their teeth than females do. Stingrays tend to have drab coloration, but river stingrays in particular often have various patterns and markings over the brown or gray background. /=\

Fishermen in rivers of many parts of the world fear the often abundant stingrays. River stingrays lie half buried on the bottom. Like marine stingrays, if stepped on, they can whip their tails upward to deliver a penetrating sting with their spines. The stinging cells of freshwater stingray branch out beyond the lateral grooves to cover a larger surface area along the entire blade. Due to this large area and an increased number of proteins within the cells, the venom of freshwater stingrays has a greater toxicity than that of marine stingrays.

Five species of river ray have been listed as potentially Endangered, but there is insufficient data to make a definite determination. River rays begin breeding in September or October. The young are usually born in February, but the duration of pregnancy depends on the specific geographic region. Gestation may take up to 12 months. Within any given group of rays, individuals appear to go through mating, gestation, and parturition (birth) at the same time as all the other females in the group.

Sixgill Stingrays

six gill stingray

Sixgill Stingrays (Scientific name: Hexatrygonidae) are unique in that they have six pairs of gill openings and six gill arches, rather than five. They also have a distinctive triangular long snout, confluent with the rest of the disc created by the pectoral fins. They have a functional sting, but no reports of negative effects on humans have been reported. [Source: Monica Weinheimer, Animal Diversity Web (ADW)]

Sixgill stingrays are found in temperate and tropical marine environments and live in the western Pacific from Hong Kong to Japan, and off the coast of South Africa. They are found near Australia over the continental slope. They feed on small fishes and invertebrates. They in turn are preyed upon by sharks.

According to Animal Diversity Web: They are unique among rays in that their spiracles (respiratory openings) are closed with an external valve flap, rather than an internal valve. The spiracles are large and far behind the eyes. The snout is long and triangular, measuring over a third of the total disc length. The snout, which is confluent with the rest of the disc, is translucent, depressed (thin), and some investigators suggest that it may be used as an electroreceptive organ. The nostrils are set wide apart, as are the eyes. The mouth is broad and contains many small, blunt teeth. The disc is longer than it is wide, and has smooth skin with no denticles or thorns: “an unusually flabby ray.”

Sixgill stingrays have no dorsal fin. They do have small pelvic fins and a long, low caudal fin that reaches the tip of the tail. The tail is short, slender, not whip-like, and bears one or two serrated stinging spines. These rays are brownish pink, with a pale snout and dark caudal fin. Adults can measure up to 2 meters long. Some researchers, however, note that the flexible snout tip, which can move both laterally and vertically, may be used to probe for food in sand or mud.

Butterfly Rays

Butterfly Rays (Scientific name: Gymnuridae) is a family of rays with two genera and about 12 species. Their common name — butterfly rays — is derived from the fact that their pectoral fins form a disc that is much broader than it is long, forming “wings” that resemble those of a butterfly. These rays live marine environments and sometimes estuaries. They are bottom-dwellers that feed on a variety of crabs, shrimps, invertebrates, fishes, small crustaceans, and mollusks.. Some have a venomous spine on their short tails, but butterfly rays are considered far less dangerous than long-tailed stingrays. [Animal Diversity Web (ADW) /=]

Butterfly rays are found worldwide in tropical and warm temperate seas. They are widely distributed in the Pacific and Indian oceans and can heir range in the Atlantic includes the Mediterranean and Black Seas. They have been most commonly observed on the upper continental shelf. They prefer stretches of open sand and frequent shallow beaches and bays. Their main reproductions are sharks. Butterfly rays are eaten by some people and commonly caught as bycatch by commercial fishermen. In Australia, cuts from one species of butterfly ray are sometimes sold as skate flesh. Currently, there is no conservation threat to any member of this family.

According to Animal Diversity Web: Their pectoral fins create a disc that is more than 1.5 times as broad as it is long and extends forward to include the head, ending in a blunt, angular, short snout. The snout is rounder and blunter on females than on males, at least in the case of Gymnura micrura. The disc is brown, grayish, purplish or greenish in color, sometimes with pale and dark spots, and it may be naked or covered with small denticles. The head is even with the disc rather than elevated, giving the fish a very flat appearance from the side view. The eyes are located on the sides of the top of the head, with the spiracles (respiratory openings) close behind the eyes.

Their mouths are relatively large and located under the end of the snout. Since their mouths are directed downward and often placed against the sand, bottom-living rays use their spiracles rather than their mouths for water intake, and, if the gills are covered with sand, the spiracles are also used for expelling water. Butterfly rays have small, cuspidate teeth that do not form the crushing plates found in many other rays. Their dorsal fins, if present, are small. They lack anal fins, and rather than a caudal fin they may have low dorsal and ventral ridges on the tail. The slender tail is much shorter than the disc. Some butterfly rays have a stinging spine behind the pelvic fins. These fish range in size from less than 0.5 meters long to over two meters long.

Butterfly rays usually bear between two and six live young at a time, after nourishing the embryos with milky fluid (histotroph) secreted by the uterus Embryos are so well nourished in the uterus that in Gymnura micrura, for example, the young ray’s net weight increases by 4900 percent from egg to birth, and are between 15-22 centimeters when they are born. Development in the uterus usually takes about two to four months. One species of butterfly ray, Gymnura natalensis, is born with an almost triangular shape, but develops much wider pectoral fins as it grows, and in adults the disc is more than twice as broad as it is long.

Round Stingrays (Stingarees)

common stingray

Round stingrays (Scientific name: Urolophidae) are also known as round rays and stingarees. Relatively small rays, they are members of the Urolophidae family, which consists of two genera and about 35 species of bottom-dwelling rays that live in warm seas. They usually lying partially buried under the sand. Their rounded pectoral discs are colored to blend in with the sand, mud, or rocks where they live. Urolophids feed on a variety of invertebrates, small fishes, and crustaceans. Their tails are notable by the presence of a well-developed caudal fin, are equipped with one or more serrated stinging spines. Like other rays round stingrays give birth to live young that developed in the body of the mother. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]

Many round stingrays feed on fishes, worms, shrimps, and other small organisms they uncover when they flap their pectoral fins along the bottom. Some are able to eat hard-shelled mollusks and crustaceans. Their main known predators are sharks Ray spines, some of them likely belonging to round stingrays, have been found embedded in the mouths of many sharks. For defense the rays have their spins and camouflage coloring that blends in with the sandy or rocky bottom. Some researchers describe round stingrays as almost impossible to find unless they move.

Round stingrays live in temperate, tropical, saltwater and marine environments. They reside in coastal areas, brackish water and on the sea bottom as well as in estuaries and intertidal areas. They are found in the western Atlantic, including the Caribbean Sea, and the eastern Atlantic as well as the Indian Ocean, the Mediterranean Sea and western Pacific, In the eastern Pacific they range from California to Chile.

Round stingrays are marine fish but they sometimes enter estuaries. They live mainly along coastlines and along the continental shelf in relatively shallow water but some occupy depths of at least 700 meters (2,300 feet) down the continental slope. They generally prefer sandy bottoms in which they can bury themselves, but a few species live on rocky sea bottoms or areas of sea vegetation such sea grass beds and kelp forest. Round stingrays generally have patterns and coloring that blends in with their surroundings. /=\

Round Stingray Characteristics

Round stingrays tend to be small, generally less than 76 centimeters (two feet) in length exclduing their tail. According to Animal Diversity Web: They are rays with a rounded, oval, or rhomboidal disc created by the pectoral fins. The disc is less than 1.3 times as broad as it is long. Their snouts are confluent with the rest of the disc. From the side they appear relatively flat, with the head not elevated. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]

The spiracles (respiratory openings) are close behind the eyes, which are dorsolateral (above and to either side) on the head. The mouth is small and located on the underside of the snout, and often has several papillae on its floor. Teeth are small and do not form flat crushing plates as in some other rays. There are five pairs of small gill openings, and the internal gill arches do not have filter plates or ridges. Some round stingrays lack a dorsal fin; in others the fin is small, located just in front of the sting and behind the pelvic fins.

The serrated stinging spine, located about halfway down the tail, is large and functional. A distinguishing feature of these rays is the presence of a moderately large, elongated caudal fin that extends to the tip of the tail. In the genus Urolophus the caudal fin lobes are confluent, while in the genus Urotrygon they are separate. The tail is slender but not whip-like, and shorter than in stingrays. In coloration round stingrays range from uniform grayish, yellowish, or brownish, to patterns of spots, reticulations, or dark mask-like bands. Their discs may be smooth or covered with small denticles.

Round Stingray Behavior and Reproduction

round stingray

Round stingrays appear to spend most of their time partially buried in the sand, or, for a few species, lying on rocks or among sea vegetation. They flap their pectoral fins to bury themselves with sand, and also to uncover the benthic (bottom-dwelling) organisms on which they feed. If stepped on they can thrust their flexible tails upward to deliver a sting with their tail spines. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]

Round stingrays can be social and form social groups. They communicate with vision, touch and chemicals usually detected by smelling and sense using vision, touch, sound, electric signals, magnetism and chemicals usually detected with smelling or smelling-like senses. In lab experiments, members of the round stingray family changed their feeding location according to artificially induced changes in the electrical field around them.

Round stingrays are viviparous (they give birth to live young that developed in the body of the mother) and iteroparous (offspring are produced in groups such as litters multiple times in successive annual or seasonal cycles). They engage in internal reproduction in which sperm from the male fertilizes the egg within the female and engage in seasonal breeding. There is no evidence of post-birth parental care. After an extended nurturing period inside their mothers’ bodies, young rays are born live to feed and fend for themselves.

Round Stingrays, Humans and Conservation

Round stingrays are seldom purposely commercially fished but they are frequently caught in large numbers in nets as bycatch. Several species have eaten. Some are reported to be “chewy unless prepared properly.” Native peoples in many parts of the family’s range have used ray spines for spear tips, daggers, or whips. Because of their low birth rates and sometimes restricted range, round stingrays are susceptible to human activity, although only one species is currently known to be threatened. There is Little specific information regarding lifespans but is assumed they grow and mature slowly and are long-lived. As is the case with other rays. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]

Round stingrays can cause serious wounds with their tail spines. The serrated spine tip can be difficult to remove without surgery if it breaks off in the wound. Because they tend to occupy shallow water and are often colored to blend in with the bottom, they are a hazard to swimmers, waders and beachgoers. /=\

Round stingrays have not been evaluated by the International Union for Conservation of Nature (IUCN) Red List: One species in the Australian genus Urolophus is listed as near threatened. It lives in an area of intensive fishing and females often abort embryos when captured and they only bear two young at a time anyway.

Bluespotted Ribbontail Rays

Bluespotted ribbontail rays (Scientific name:Taeniura lymma) are also known as lagoon rays, fantail rays, blue-spotted stingray and ribbon-tailed stingrays. They are colorful, often-photographed fish found in the Indo-Pacific region. Reaching a length of two meters and a weight of 30 kilograms, they possess blue spots scattered over a greenish or yellowish body, with blue strips running along the sides of its tail. The species is often found in sandy areas next to reefs and rests in cave or crevices, These rays both forage for food and lie in wait in the sand for prey to come their way. The tail contains a powerful toxin that can result in a nasty sting if the ray is mishandled or stepped on.

blue-spotted ribbontail ray

The body of bluespotted ribbontail ray contains no bones; instead it is held together by cartilage. The stinging barbs on its tail can be regenerated if broken off. It is said the venom contained within the stinging barbs can be broken down by heat and thus soaking a wound caused by a barb in hot water can break down the venom and reduce the pain. But this claim has not been verified. Bluespotted ribbontail rays are that it is one of the few species of rays that can retain their urine. [Source: Jennifer Miller, Animal Diversity Web (ADW) /=]

Bluespotted ribbontail rays are found primarily in the Indo-west Pacific, mostly in shallow continental shelf waters in temperate and tropical seas. They prefer areas with sandy or sedimentary substrates in which they bury themselves. They are typically found at depths of less than 25 meters (82 feet), often near coral reefs. In Australia, these rays have been observed from Ningaloo Reef, Western Australia to Bundaberg, Queensland. They have also been recorded in southern Africa, the Red Sea and the Solomon Islands. Bluespotted ribbontail ray are most numerous close to shore. They have been observed around coral rubble and shipwreck debris. Divers and snokelers often locate this ray by detecting its distinctive ribbon-like tail poking out from a crack in the coral.

The bluespotted ribbontail ray’s beautiful coloration makes it a popular aquarium fish. In Australia, it is often eaten and hunted for its meat. It is said they are very hard to take care of in an at-home aquarium. The sting of the blue-spotted stingrays can be very painful. Although this species is very wide ranging and common, it is threatened by capture for food and the marine aquarium fish trade. It is also hurt by damage to coral reefs. The International Union for Conservation of Nature (IUCN) Red List lists these rays as “Near Threatened”; They have no special status according to the Convention on the International Trade in Endangered Species (CITES). Because this species has a long gestion period and only about seven live young are produced in each litter, it is vulnerable to population collapses from overfishing and habitat loss. /=\

Bluespotted Ribbontail Ray Characteristics and Behavior

Bluespotted ribbontail rays are colorful stingrays with distinct, large, bright blue spots on their oval, elongated bodies. Their snout is rounded and angular with broad outer corners and their Its caudal fin is broad and reaches to the tip of the tail. Their disc diameter reach lengths of 95 centimeters (37.4 inches), with their average length being 25 centimeters (9.84 inches). The tail tapers and can be equal to or slightly less long than the body length. At the tip of the tail are two sharp venomous spines. Adults are olive-gray or gray-brown to yellow on their backside, and white on the bottom with numerous blue spots. Juveniles are pale gray or brown and the spots are black or rusty red and white. These patterns and markings are distinct to each individual. [Source: Jennifer Miller, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: The tail of Bluespotted ribbontail ray can be easily recognized by the blue side-stripes found on either side. It has large spiracles that lie very close to its large eyes. The mouth is found on the underside of the body along with the gills. Within the mouth are two plates, which are used for crushing the shells of crabs, prawns, and mollusks. Propulsion is achieved using its pectoral fins which make up the bulk of its oval, disc shaped body. Blue-spotted stingrays have fin muscles which are found throughout the entire length of the fin. All of these muscles are active except at low speeds when they are not needed to propel the body through water. /=\

Blue-spotted stingrays may be found alone or in small groups, mostly in shallow waters over reef flats. they are rather shy and will usually swim away rapidly if disturbed by divers. When threatened, blue-spotted stingrays will use their venomous tail to inject poison. The venom is produced and delivered into narrow groves running lengthwise along the underside of the stinger. The entire structure is covered by a thin layer of skin which, when broken, releases its venom into its victim.

Bluespotted ribbontail rays communicate with electric signals and chemicals detected by smelling and sense using vision, touch, electric signals and chemicals usually detected with smelling or smelling-like senses. They use electroreception to communicate with other bluespotted ribbontail rays. Structures called the ampullae of Lorenzini allow them to detect slight electrical impulses within the water. /=\

Bluespotted Ribbontail Ray Food, Eating Behavior and Predators

Blue-spotted stingrays feed on a wide variety of sea creatures — bony fish, crabs, shrimp, polychaetes and other benthic invertebrates living on or near the bottom of the sea . Since their mouths are located on the underside of the body, prey is trapped by pressing it prey into the sea floor with their discs and then directed into the mouth by maneuvering the disc over the prey. [Source: Jennifer Miller, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: The bluespotted ribbontail ray has very distinct feeding behaviors. During high tide, it migrates in groups into shallow sandy areas of tidal flats to feed on sand worms, shrimps, hermit crabs, and small fishes. At low tide it recedes back into the ocean, usually alone to hide in the coral crevices of the reef.

Bluespotted ribbontail ray can detect its prey through an electroreceptor system. The nostrils are partly covered with a broad fleshy lobe, known as the internasal flap. This is covered in sensory pores and extends to the mouth. These pores form part of the ampullae of Lorenzini (the electrorecption system.) This electroreceptor system can detect electrical fields produced by the prey. This electroreceptor system cannot only be used to detect prey but can also be used to detect predators and other members of the same species. /=\

The most dangerous predator to blue-spotted stingrays are human beings. Besides humans, the only other type of predator known to this species of stingrays is the hammerhead shark. Hammerheads are able to avoid being stung by the poisonous spines of stingrays by pinning them down.

Bluespotted Ribbontail Ray Mating, Reproduction and Offspring

Bluespotted ribbontail ray are ovoviviparous (eggs are hatched within the body of the parent) and iteroparous (offspring are produced in groups such as litters). They engage in internal reproduction in which sperm from the male fertilizes the egg within the female. The breeding season is from late spring through the summer.The gestation period ranges from 4 to 12 months. , The average number of offspring being seven. [Source: Jennifer Miller, Animal Diversity Web (ADW) /=]

During courtship, the male often follows the female putting his sensitive nose close to her cloaca in search of a chemical signal that the female emits. Courtship usually includes some sort of nibbling or biting of the disc. The teeth of the male are used to hold the female in place during population. The male fertilizes the female via internal fertilization through the use of his claspers. /=\

Bluespotted ribbontail ray embryos are nourished by the yolk of eggs and the eggs are retained within the female until they hatch.. When blue-spotted stingrays are born, they hatch out of egg cases, bearing the same distinctive blue markings as adults and looking like miniature versions of adults. When born, the young stingrays are about nine centimeters (3.5 inches) long. Young are born out of the egg cases with soft tails encased in a thin layer of skin to prevent injury to the mother during birth. The skin is eventually lost and the tail becomes a valuable protective devise at a young age. /=\

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023