White-edge freshwater whipray
A rare freshwater stingray with a white-edged disc and venomous tail spines.
The white-edge freshwater whipray (*Fluvitrygon signifer*) is a stingray from the Dasyatidae family found only in four river systems across Southeast Asia. Its oval pectoral fin disc can reach 60 cm (24 in) across, and its tail is very long and whip-like, lacking any fin folds. The ray is easily recognized by a sharp, white band that runs along the edge of its otherwise brown disc, a white tail, and a band of rough, tooth-like scales (dermal denticles) down the middle of its back. It feeds on small bottom-dwelling creatures and gives birth to live young, with embryos nourished by a uterine milk-like substance. The two long spines on its tail are venomous and can be dangerous to people. The IUCN lists this species as Endangered, threatened by fishing and the loss, degradation, and fragmentation of its habitat.
The species was first described in 1982 by Leonard Compagno and Tyson Roberts, who gave it the name *signifer* (Latin for "sign-bearing") because of its unique coloring. The original specimen—an immature female 29 cm (11 in) across—was collected from the mouth of the Sungai Ketungau, part of the Kapuas River in West Kalimantan, Indonesia. It is also known as the freshwater stingray, pale whipray, or white-rimmed stingray. Within its genus, it most closely resembles *Fluvitrygon kittipongi*, described in 2005. A 1999 genetic study using cytochrome b sequences showed it is closely related to *Maculabatis gerrardi* and *Brevitrygon imbricata*, which form a sister pair.
This ray is one of the few members of its family that lives exclusively in fresh water. It is known from the Kapuas River (Borneo), the Indragiri River (Sumatra), the Perak River (Peninsular Malaysia), and the Chao Phraya River (Thailand). Though these rivers are now separated, during the Pleistocene (2.6 million to 12,000 years ago), when sea levels were lower, they may have been connected as part of a larger drainage basin in Central or North Sundaland. This would have allowed the ray to spread into its current range without entering salt water. It is a bottom-dweller that prefers sandy habitats.
The disc of the white-edge freshwater whipray is thin, oval, and slightly wider than long. The front edges meet at a broad angle at the tip of the snout, which sticks out a little. Its eyes are small, and just behind them are much larger spiracles.
Quick Facts
- Genus
- Fluvitrygon
- Species
- signifer
Facts from the source article.
Lore & Background
The white-edge freshwater whipray was described by Leonard Compagno and Tyson Roberts in a 1982 issue of Environmental Biology of Fishes, with the specific epithet signifer (Latin for 'sign-bearing') in reference to its distinctive coloration. The type specimen is an immature female 29 cm (11 in) across, collected from the mouth of the Sungai Ketungau off the Kapuas River in West Kalimantan, Indonesia. Other common names include freshwater stingray, pale whipray, and white-rimmed stingray. Within its genus, it most closely resembles Fluvitrygon kittipongi, described in 2005. A 1999 phylogenetic analysis, based on cytochrome b sequences, found that it is closely related to Maculabatis gerrardi and Brevitrygon imbricata, which form a sister species pair.
This ray has a thin and oval pectoral fin disc slightly wider than long, with a sharply delineated white band running around the margin of its otherwise brown disc. Its tail is about 3.5 times as long as the disc and bears two stinging spines on top; behind the spines the tail becomes slender and whip-like, without any fin folds. A band of dermal denticles runs along the middle of its back. It feeds on benthic invertebrates and is aplacental viviparous. The white-edge freshwater whipray retains the ability to synthesize urea for osmoregulation and can survive in brackish water with a salinity of 20 ppt for at least two weeks. Its ampullae of Lorenzini are intermediate in size and structure between those of marine relatives and potamotrygonid stingrays.
Reader's Guide
The white-edge freshwater whipray is significant as one of the few members of its family that seems to exclusively inhabit fresh water, known from four Southeast Asian river systems: the Kapuas River in Borneo, the Indragiri River in Sumatra, the Perak River in Peninsular Malaysia, and the Chao Phraya River in Thailand. These rivers may have been contiguous during the Pleistocene epoch when sea levels were low, allowing the ray to disperse without entering salt water. The species is extremely rare, with only about 10 specimens having been deposited in museum collections. Its venomous stings are capable of inflicting excruciating and even fatal wounds on humans. The International Union for Conservation of Nature (IUCN) has assessed it as Endangered, due to heavy pressure from fishing and habitat loss, degradation, and fragmentation. Dams built on the Chao Phraya in Thailand have fragmented the resident stingray population and reduced its genetic diversity. The Thai government began a captive breeding program for this and other endangered freshwater stingrays at Chai Nat during the 1990s, but by 1996 the program had been placed on hold.
Did You Know?
- Only about 10 specimens of this species have been deposited in museum collections.
- Its tail spines can reach up to 87 mm (3.4 in) long with up to 89 serrations.
- The Thai government began a captive breeding program for this ray at Chai Nat during the 1990s, but it was placed on hold by 1996.
More in Reef Sharks and Rays, Part 2 1-24
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