Stingray, Giant Freshwater (Himantura Chaophraya)
The Giant Freshwater Stingray in Thailand is believed to be the largest freshwater fish on the planet reaching weights approaching 1000 lbs.
The prehistoric Giant freshwater stingray 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 highly understudied ancient predator is one of the largest living Dasyatidae (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 Giant freshwater stingray 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 mollusk 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 environments and is possibly the largest freshwater fish on the planet.
This mighty Paleozoic freshwater predator is easily identifiable due to its immense rounded disc-like shape measuring up to three metres in width with a prominent snout tip and whip-like tail.
The central section of the disc-like body of the stingray is houses the stingray’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 the freshwater stingray a limited field of vision of the water column above whilst buried in the muddy riverbed.
Directly behind the eyes of the Giant freshwater stingray is the spiracle area often referred to as the ‘sixth gill’ which acts as a primitive type of snorkel. This evolutionary 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 Giant freshwater stingray’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 of the stingray 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 allows 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 smooth underside/ventral side of the prehistoric stingray.
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 of the freshwater stingray 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 elasmobranches 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 fossils 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 claspers in this region.
This king of freshwater predators the ‘Giant freshwater stingray’ preys on fish, crustaceans, mollusks and other aquatic invertebrates. Himantura Chaophraya is considered threatened at the time of writing and is listed as vulnerable on the IUCN red list.
At the time of writing he Fishsiam team in Thailand has successfully captured and released four hundred and fifty Giant freshwater Stingray whilst fishing at the Ban Pakong River and Maeklong River in Thailand.
Fishsiam has featured in numerous TV documentaries concerning Giant Freshwater Stingrays in Thailand with our most recent notable appearances being with National Geographic explorer Dr.Zeb Hogan and Jeremy Wade River Monsters on Animal Planet.
In January 2009 the world’s first comprehensive attempt to scientifically study the amazing Giant Freshwater Stingray in Thailand began with National Geographic explorer Dr.Zeb Hogan and Dr.Nantaika Chansue from Chulalongkorn University working in collaboration with the Fishsiam team in Thailand.
During the highly adventurous and pioneering two week Giant freshwater stingray fishing expedition the scientists assisted by the fishermen conducted groundbreaking research and scientific examinations on various Giant Freshwater stingrays caught whilst fishing at the Maeklong River and Ban Pakong River in Thailand.
During the course of the two week Giant Freshwater Stingray expedition sixteen different Giant freshwater stingrays were captured to a record breaking estimated 300-350 kg’s and made available to the aquatic scientists.
Throughout the Giant Freshwater Stingray research expedition Dr.Zeb Hogan and Dr.Nantaika Chansue collected crucial scientific data from the Giant freshwater stingrays with assistance from the Department of Fisheries.
The groundbreaking stingray research expedition saw the scientists collecting DNA, Blood and Tissue samples in addition to conducting toxicology tests on the necrotic poison from the barbs of the freshwater stingrays.
During the course of the expedition, which saw us stingray fishing every day several Giant freshwater stingrays were surgically implanted with acoustic tags by the scientists. The miniature acoustic tags after being expertly surgically implanted inside the stingrays where firmly sealed with sutures and treated with antiseptic ointment.
After releasing the acoustically implanted stingrays back into the Maeklong River, several acoustic receivers were strategically deployed at various points in the Maeklong River to monitor the movements of the tagged fish.
Further comparison of blood samples taken from captive Giant freshwater Stingrays with wild Giant freshwater stingrays caught from the Maeklong River indicated highly increased health levels in the wild Giant freshwater stingray population in Thailand.
Cutting edge scientific analysis conducted by the Chulalongkorn research team in Bangkok of toxicology samples taken from the barbs of the stingrays has revealed a close chemical signature to that of the highly necrotic venom of a Pit Viper snake.
During the course of other research expeditions in Thailand we observed a degree of social interaction between the Giant freshwater stingrays, with hooked Giant freshwater stingray being followed up to the surface layers by other Giant freshwater stingrays on several occasions.
Whilst freshwater stingray fishing in Thailand we have captured several pregnant Giant freshwater stingrays which have miraculously given birth to live young.
Newborn Giant freshwater stingray young are born in perfect miniature and generally measure between 34cm -40cm. Giant freshwater stingrays are born in mixed sex groups consisting of both male and females.
During ultrasound examinations of Giant Freshwater stingrays caught whilst fishing in Thailand we have observed pregnant females to hold between 4-6 unborn Giant freshwater stingrays.
At the time of birth and prior to birth infantile Giant freshwater stingrays have small rounded caps on the end of their barbs. It is thought that these ‘barb protectors’ are shed as the young Giant freshwater stingray grow older.
Other interesting scientific data obtained during the research of pregnant Giant freshwater stingrays has shown blood samples taken from pregnant Giant freshwater stingrays to clot almost immediately. This coagulation of the blood from pregnant female stingrays is suspected to be an evolutionary defensive mechanism in the blood designed to stop blood leakage during birth and the attraction of predatory species as in other Shark species.
Giant freshwater stingray research in Thailand is still ongoing at the Maeklong River with the majority of fish caught by our clients now examined by veterinary scientists post capture.
Fishsiam Ltd is extremely proud to be the only fishing company in the world assisting with the scientific research of the Giant freshwater stingray in Thailand and is committed to the continued scientific study of this most enigmatic and under studied monster fish species.