White-edge freshwater whipray
Encyclopedia
The white-edge freshwater whipray (Himantura signifer) is an extremely rare species
of stingray
in the family
Dasyatidae, native to four river systems in Southeast Asia
. Measuring up to 60 cm (23.6 in) across, this ray has an oval pectoral fin disc and a very long, whip-like tail without fin folds. It can be identified by the presence of a sharply delineated white band running around the margin of its otherwise brown disc, as well as by its white tail and a band of dermal denticles along the middle of its back. This species feeds on benthic invertebrate
s and is aplacental viviparous. Its two long tail spines are potentially dangerous to humans. The International Union for Conservation of Nature (IUCN) has assessed the white-edge freshwater whipray as Endangered, as it is under heavy pressure from fishing
and habitat loss, degradation, and fragmentation
.
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 (11.4 in) across, collected from the mouth of the Sungai Ketungau off the Kapuas River
in West Kalimantan
, Indonesia
. Other common name
s for this species include freshwater stingray, pale whipray, and white-rimmed stingray. Within its genus, the white-edge freshwater whipway most closely resembles H. kittipongi, described in 2005. A 1999 phylogenetic analysis, based on cytochrome b
sequences, found that it is closely related to H. gerrardi and H. imbricata, which form a sister species pair.
, the white-edge freshwater whipray is 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
. Although these rivers are now isolated from one another, when sea level
s were low during the Pleistocene
epoch
(2.6 million to 12,000 years ago) they may have all been contiguous as part of the Central or North Sundaland
drainage basin
. At that time, this ray could have dispersed into its present range without having to enter salt water
. This bottom-dwelling species favors a sandy habitat
.
s. There is a flap of skin between the nares with a fringed, subtly concave or three-lobed posterior margin. The mouth is gently bow-shaped, with a groove running from the nasal flap around its corners. There are 38–45 upper tooth rows and 37–46 lower tooth rows; the teeth are well-spaced and arranged in a quincunx
pattern. Each tooth has a blunt conical crown with a transverse cutting edge; this edge is higher and serrated in males and lower and blunt in females. There is a row of 4–5 papilla
e across the floor of the mouth: a large inner pair, a smaller outer pair, and sometimes a central one of varying size.
The 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. Two recorded individuals had tail spines 86 and 87 mm (3.4 and 3.4 in) long with 70 and 89 serrations respectively. A band of skin running along the back from between the eyes to the tail base is roughened by small, flattened heart-shaped dermal denticles interspersed with small conical denticles. There are more denticles on the tail behind the spines, and small individuals also have a pearl spine in the center of the disc. The disc is brown above, with mottling in the center and on the tail base, a white spot between the eye and spiracle, and a sharp white band running around its periphery. The underside is completely white, as is the tail behind the spines. This ray grows up to 60 cm (23.6 in) across and perhaps over 2 m (6.6 ft) long.
members of its family, but unlike the specialized South American river stingrays of the family Potamotrygonidae
, 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 the large, complex ampullae of its marine relatives and the small, simple ampullae of potamotrygonid stingrays, which may be a consequence of varying salinities in its environment and demands that would place on electroreception
. The white-edge freshwater whipray feeds mainly on small benthic organism
s, including crustacean
s, molluscs, and insect
larva
e. Reproduction is aplacental viviparous with the developing embryo
s sustained by maternally produced histotroph ("uterine milk"), as is the case in other stingrays. Newborns measure 10–12 cm (3.9–4.7 in) across; males and females mature sexually
at 21–23 cm (8.3–9.1 in) and 25–26 cm (9.8–10.2 in) across respectively.
ous stings of the white-edge freshwater whipray are capable of inflicting excruciating and even fatal wounds on humans. This species is extremely rare, with only about 10 specimens having been deposited in museum collections. Most of its range is subject to heavy fishing pressure; this ray is infrequently caught using fish trap
s, spears, and bottom-set lines; it is sold for meat and the aquarium trade
. Habitat loss and degradation, from pollution
, logging
, and dam
construction, likely poses a greater threat to the survival of this species. In Thailand, dams built on the Chao Phraya have fragmented the resident stingray population and effectively reduced its genetic diversity
. Because of diverse threats faced by this ray and the lack of exchange between the different rivers it inhabits, the International Union for Conservation of Nature (IUCN) has assessed the white-edge freshwater whipray as Endangered. 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Dasyatidae, native to four river systems in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
. Measuring up to 60 cm (23.6 in) across, this ray has an oval pectoral fin disc and a very long, whip-like tail without fin folds. It can be identified by the presence of a sharply delineated white band running around the margin of its otherwise brown disc, as well as by its white tail and a band of dermal denticles along the middle of its back. This species feeds on benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s and is aplacental viviparous. Its two long tail spines are potentially dangerous to humans. The International Union for Conservation of Nature (IUCN) has assessed the white-edge freshwater whipray as Endangered, as it is under heavy pressure from fishing
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
and habitat loss, degradation, and fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
.
Taxonomy and phylogeny
The white-edge freshwater whipray was described by Leonard CompagnoLeonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
and Tyson Roberts in a 1982 issue of Environmental Biology of Fishes, with the specific epithet signifer (Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "sign-bearing") in reference to its distinctive coloration. The type specimen is an immature female 29 cm (11.4 in) across, collected from the mouth of the Sungai Ketungau off the Kapuas River
Kapuas River
The Kapuas River is a river in the Indonesian part of Borneo island, at the geographic center of Maritime Southeast Asia. At in length, it is the longest river of Indonesia and one of the world's longest island rivers...
in West Kalimantan
West Kalimantan
West Kalimantan is a province of Indonesia. It is one of four Indonesian provinces in Kalimantan, the Indonesian part of the island of Borneo. Its capital city Pontianak is located right on the Equator....
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for this species include freshwater stingray, pale whipray, and white-rimmed stingray. Within its genus, the white-edge freshwater whipway most closely resembles H. kittipongi, described in 2005. A 1999 phylogenetic analysis, based on cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
sequences, found that it is closely related to H. gerrardi and H. imbricata, which form a sister species pair.
Distribution and habitat
One of the few members of its family that seems to exclusively inhabit fresh waterFresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
, the white-edge freshwater whipray is known from four Southeast Asian river systems: the Kapuas River in Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
, the Indragiri River
Indragiri River
The Indragiri River is a river in Sumatra, in the Indonesian province of Riau. It is formed from the union of the Ombilin River and the Sinamar River, and empties into the Strait of Malacca....
in Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, the Perak River
Perak River
Perak River is the second longest river in Peninsular Malaysia after Pahang River in Pahang, Malaysia. A number of towns are on the banks of the river including the royal town of Kuala Kangsar...
in Peninsular Malaysia
Peninsular Malaysia
Peninsular Malaysia , also known as West Malaysia , is the part of Malaysia which lies on the Malay Peninsula. Its area is . It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the island of Sumatra...
, and the Chao Phraya River
Chao Phraya River
The Chao Phraya is a major river in Thailand, with its low alluvial plain forming the centre of the country. It runs through Bangkok, the capital city, and then empties into the Gulf of Thailand.-Etymology:...
in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
. Although these rivers are now isolated from one another, when sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
s were low during the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
epoch
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
(2.6 million to 12,000 years ago) they may have all been contiguous as part of the Central or North Sundaland
Sundaland
Sundaland is a biogeographical region of Southeastern Asia which encompasses the areas of the Asian continental shelf that was exposed during the last ice age. It included the Malay Peninsula on the Asian mainland, as well as the large islands of Borneo, Java, and Sumatra and their surrounding...
drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
. At that time, this ray could have dispersed into its present range without having to enter salt water
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
. This bottom-dwelling species favors a sandy habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
.
Description
The white-edge freshwater whipray has a thin and oval pectoral fin disc slightly wider than long. The anterior margins of the disc converge with a broad angle at the tip of the snout, which is slightly protruding. The eyes are small and immediately followed by much larger spiracleSpiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. There is a flap of skin between the nares with a fringed, subtly concave or three-lobed posterior margin. The mouth is gently bow-shaped, with a groove running from the nasal flap around its corners. There are 38–45 upper tooth rows and 37–46 lower tooth rows; the teeth are well-spaced and arranged in a quincunx
Quincunx
A quincunx is a geometric pattern consisting of five points arranged in a cross, that is five coplanar points, four of them forming a square or rectangle and a fifth at its center...
pattern. Each tooth has a blunt conical crown with a transverse cutting edge; this edge is higher and serrated in males and lower and blunt in females. There is a row of 4–5 papilla
Papilla (fish mouth structure)
The papilla, in certain kinds of fish, particularly rays, sharks, and catfish, are small lumps of dermal tissue found in the mouth, where they are "distributed uniformly on the tongue, palate, and pharynx"...
e across the floor of the mouth: a large inner pair, a smaller outer pair, and sometimes a central one of varying size.
The 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. Two recorded individuals had tail spines 86 and 87 mm (3.4 and 3.4 in) long with 70 and 89 serrations respectively. A band of skin running along the back from between the eyes to the tail base is roughened by small, flattened heart-shaped dermal denticles interspersed with small conical denticles. There are more denticles on the tail behind the spines, and small individuals also have a pearl spine in the center of the disc. The disc is brown above, with mottling in the center and on the tail base, a white spot between the eye and spiracle, and a sharp white band running around its periphery. The underside is completely white, as is the tail behind the spines. This ray grows up to 60 cm (23.6 in) across and perhaps over 2 m (6.6 ft) long.
Biology and ecology
Like the other freshwater and euryhalineEuryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
members of its family, but unlike the specialized South American river stingrays of the family Potamotrygonidae
Potamotrygonidae
River stingrays are Neotropical freshwater fishes of the Potamotrygonidae family .They are native to northern, central and eastern South America, living in rivers that drain into the Caribbean, and into the Atlantic as far south as the Río de la Plata in Argentina...
, the white-edge freshwater whipray retains the ability to synthesize urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
for osmoregulation
Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
and can survive in brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
with a salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
of 20 ppt for at least two weeks. Its ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
are intermediate in size and structure between the large, complex ampullae of its marine relatives and the small, simple ampullae of potamotrygonid stingrays, which may be a consequence of varying salinities in its environment and demands that would place on electroreception
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
. The white-edge freshwater whipray feeds mainly on small benthic organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s, including crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, molluscs, and insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. Reproduction is aplacental viviparous with the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s sustained by maternally produced histotroph ("uterine milk"), as is the case in other stingrays. Newborns measure 10–12 cm (3.9–4.7 in) across; males and females mature sexually
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 21–23 cm (8.3–9.1 in) and 25–26 cm (9.8–10.2 in) across respectively.
Human interactions
The venomVenom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous stings of the white-edge freshwater whipray are capable of inflicting excruciating and even fatal wounds on humans. This species is extremely rare, with only about 10 specimens having been deposited in museum collections. Most of its range is subject to heavy fishing pressure; this ray is infrequently caught using fish trap
Fish trap
A fish trap is a trap used for fishing. Fish traps may have the form of a fishing weir or a lobster trap. A typical trap might consist of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of...
s, spears, and bottom-set lines; it is sold for meat and the aquarium trade
Fishkeeping
Fishkeeping is a popular hobby concerned with keeping fish in a home aquarium or garden pond. There is also a fishkeeping industry, as a branch of agriculture.-Types of fishkeeping systems:...
. Habitat loss and degradation, from pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
, logging
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
, and dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
construction, likely poses a greater threat to the survival of this species. In Thailand, dams built on the Chao Phraya have fragmented the resident stingray population and effectively reduced its genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
. Because of diverse threats faced by this ray and the lack of exchange between the different rivers it inhabits, the International Union for Conservation of Nature (IUCN) has assessed the white-edge freshwater whipray as Endangered. The Thai government began a captive breeding
Captive breeding
Captive breedingis the process of breeding animals in human controlled environments with restricted settings, such as wildlife reserves, zoos and other conservation facilities; sometimes the process is construed to include release of individual organisms to the wild, when there is sufficient...
program for this and other endangered freshwater stingrays at Chai Nat during the 1990s, but by 1996 the program had been placed on hold.