Stingray, Giant Freshwater. (Himantura Chaophraya). Max weight 450 kg+/ 1000lbs. Predatory.
The Giant Freshwater Stingray is the largest freshwater fish on the planet reaching weights approaching 1000 lbs. This prehistoric relic
inhabits some of the wildest and remote waters on earth including the Mekong, Maeklong, Ban Pakong, Chaophraya, Tachin and Tapi Rivers in
Thailand and is also distributed in Borneo, New Guinea and Australia. This nomadic and understudied ancient predator is one of the largest
living Dasyatids (whip-rays) family of fishes left on the planet. The Giant Freshwater Stingray belongs to the class Chondrichthyes, which
includes all 850 species of sharks, rays, skates, and chimaeras. These fishes have cruised the oceans since the Paleozoic era. The basic
dorsoventrally compressed body plan of the ray is thought to have originated during the Jurassic period, approximately 100 Mya. This design,
coupled with a lack of a swim bladder and powerful jaws designed for crushing hard shells of molluscs such as clams and muscles, has made
the ray the successful benthic predator it is today. The Giant freshwater stingray is found throughout the great river systems of Thailand
in freshwater and estuarine enviroments and is possibly the largest freshwater fish on the planet. This mighty Paelozoic predator is easily
identifiable due to its immense rounded disc-like shape measuring upto three metres in width with a prominent snout tip and whip-like tail.
Within the central section of the disc the main body of the ray is located housing the fish’s internal organs and in some specimens
displaying the endoskeleton of the creature.
At the front of the pronounced body section small protruding ‘periscope’ eyes are located allowing it a limited field of vision
of the water column above whilst buried in the muddy riverbed. Behind the eyes is the spiracle area often referred to as the ‘sixth
gill’ which acts as a primitive type of snorkel. This adaptation allows them to breathe more easily while they are hiding in the
substrate.
The Giant Freshwater Stingray has a dark brown surface on its upper/dorsal side with a highly abrasive textured skin covered in
placoid scales, the tiny tooth-like structures that protect the skin of elasmobranchs and give it a sandpaper-like texture. The
creature’s underside is of a very smooth nature characteristically white in colour with a grey to brown colouration around the
edges. A huge cavernous mouth is located on the underside lined with highly abrasive crushing pads. Jelly-filled sensory pores
"Ampullae of Lorenzini", located on the skin around the nose and mouth on the underside of the disc, are present in most
elasmobranchs and allow sharks and rays to detect minute electric fields generated by living things. This is especially useful
for freshwater stingrays because it helps them to hunt down prey that might be buried in the riverbed or hiding in murky water.
In addition two rows of five gill slits are located on the underside/ventral side of these prehistoric predatory giants.
The Giant Freshwater Stingray is armed with two venomous barbs located close to the base of its tail which have two components:
the sharp inner barb used for piercing, and a thin sheath surrounding it that contains the venom. When the spine is deployed, the
barb pierces the venom sac along with the victim's skin, and the poisonous slime is introduced into the wound. The barb is extremely
sharp (it has been known penetrate bone), and it operates under the same principle as an arrowhead-- it slides into flesh fairly
easily, but the serrated edges make it very difficult and painful to extract. The tail is very flexible and can bend pretty much
any direction within a split second, inflicting serious damage. In addition to causing great pain, the venom contains enzymes that
cause tissue death. Similarly to the teeth or dorsal spines of a shark, stingray spines are thought to have originated from
placoid scales, the tiny tooth-like structures that protect the skin of elasmobranchs and give it a sandpaper-like texture.
Placoid scales, just like shark teeth, are lost and re-grown on a regular basis.
Determining the sex of these mighty living fossil’s is a relatively easy exercise with male specimens displaying obvious
genitalia called claspers similar to those of a shark at the base of the tail. Female specimens are easily distinguishable by
an absence of genitalia in this region.
This king of freshwater predators preys on fish, crustaceans, mollusc’s and other aquatic invertebrates. Himantura Chaophraya
is considered threatened and is listed as vulnerable on the IUCN red list.
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