Giant Freshwater Stingray Profile
You don’t usually associate rivers with dangerous fish. Mammals and reptiles, sure. There are lots of those in the freshwater. Parasites, too, are at the other end of the size spectrum. But fish, not so much. They’re all in the ocean!
But there are some dangerous fish in the rivers, too. And of all the flat, stabby water circles found in rivers, the giant freshwater stingray is perhaps the most impressive.
Giant Freshwater Stingray Facts Overview
| Habitat: | Rivers and estuaries |
| Location: | Southeast Asia |
| Lifespan: | Unknown |
| Size: | Confirmed 2.2 m (7.2 ft) across, possibly much bigger |
| Weight: | Confirmed 300 kg (660 lb), possibly up to 2000kg (4,400 lb) |
| Colour: | Black/brown |
| Diet: | Small invertebrates, crustaceans, molluscs, small fish |
| Predators: | Humans, large carnivorous fish |
| Top Speed: | Unknown |
| No. of Species: | 1 |
| Conservation Status: | Endangered (IUCN) |
Giant freshwater stingrays are a type of whipray found in Southeast Asian rivers and pack an enormous punch. These may well be the largest fish in freshwater habitats, and as stingrays, they come with a barb as standard that can hack and sting into both flesh and bone.
They’re potentially dangerous, but only if you interfere with one, and otherwise quite calm and avoidant of humans. Unfortunately, overfishing has reduced these elusive river giants and they’re now in need of looking after.
Interesting Giant Freshwater Stingray Facts
1. They’re whiprays
The species name polyepsis means “multiple scales”, and it’s one that’s commonly known as the giant freshwater whip ray, having been grouped in the genus Himantura until 2008 when it was moved into the genus Urogymnus.
But despite all this shuffling, it’s remained in the Dasyatidae family, along with all the other whiprays, or whiptail stingrays. This is the most diverse of the ray families and has around 90 species in 19 genera.
Most whiprays live in the ocean, but a handful have evolved to live in freshwater, like this giant subject, Urogymnus polylepis, who seems to be able to handle both.
These stingrays are characterised by an exceptionally long tail, giving them a whiplike appearance, and it’s used much in the same way as a whip, to defend the ray from attackers. 1
2. They sting
This might be a surprise, given the previous fact, but these whiptail rays are of course a subcategory of stingrays, and even more, they’re a freshwater subgroup among the whiptail rays.
Freshwater stingrays pack a serious punch. While all stingrays have toxins around a bony barb in the tail for defence, the toxicity of freshwater varieties appears to be more potent.
This is a cartilaginous fish with no incentive to harm anyone other than in self-defence, and would much rather be left alone. But when it isn’t, a toxic barb powerful enough to pierce bone can be deployed, and to great effect.
A sting from this barb can bring with it a plethora of unpleasant symptoms, such as headaches, nausea, vomiting, and heart arrhythmias, sometimes even seizures. But the venom itself is usually not fatal.
Curiously, though, of all the animal venoms, that of the stingray is some of the least researched. 2
3. They can be legitimately dangerous
While stingrays really got their name out there by being involved in the death of Steve Irwin, this peculiar incident was the zoological equivalent of choking to death on a sandwich. Stingrays, in general, are far less dangerous than sandwiches, and attacks are both incredibly rare and usually pretty superficial.
But common stingrays are about 45cm across and weigh around 15kg. Enormous versions of this, like the giant freshwater stingray, are potentially ten times the size and mass and pack a whipping toxic barb that is scaled appropriately.
While they share the timid and hesitant nature of their smaller cousins, a monster this size is far more dangerous when put into a position of panic by fishermen or heavy-footed tourists.
The stingers are covered by a toxin-producing glandular tissue or mucous; and as such, each sting causes intense inflammation, excruciating pain and skin necrosis. But this isn’t likely what will kill you.
The barb is around 40cm long and very sharp. It’s also at the end of a whipping tail and can cause fatal damage by itself.
The venom is just the cherry on top. If you survive the slashing machete attack of the tail, you’re in for 20 hours of unrelenting pain, and a few more days for it to gradually fade away. Of course, huge wounds like this can easily become infected, especially when necrotising venoms further damage the tissue. 3
4. They’re invasive in Brazil
So it’s fair to say they’re not very popular among fishing communities in Brazil, where this species appears to have invaded.
Locals have no familiarity with wounds from this animal, and it has made its way into populated areas where it has been stepped on more than once. Sand mining and fishing in the Brantas River has already provided us with a few cases of serious wounding by this fish and promises many more as it gets a foothold in the region.
5. They’re the largest freshwater stingray
Some call this animal the largest freshwater fish in the world. This is not yet verified, but it could be true, based on unconfirmed accounts of its size.
It’s hard to measure a fish this shape, let alone one that’s as slippery and heavy as it is. Confirmed cases show us that it grows to at least 2 meters across, and some say it can reach 5m. 500kg specimens are known, and it is hypothesised that they can grow up to four times that mass.
At its confirmed weight, it’s one of the biggest fish in the river. At its maximum possible weight, there’s nothing heavier. This would make it the largest freshwater fish. The trouble is, almost nobody has access to big round scales to get a proper reading. 4
6. They’re the largest freshwater ECG
This stingray has a huge amount of surface area, and much of this surface is taken up by sensory organs called Ampulae of Lorenzini, which are gell-filled pores, capable of picking up electrical signals.
Like sharks, rays use these organs to find prey hidden in the sand, and the sheer size of this stingray may mean it has the biggest organ of the kind in all of the fishy domains.
Its only real competition comes from the 1.5m-wide face of a whale shark, and the 5-meter flappy area of the giant manta. But since both of these live in the ocean, its title of “Biggest freshwater ECG detector” is secure.
7. They’re covered in mucous
This is one of those things that’s frowned upon in humans but is actually a great idea for some animals. Mucous is much more than just the disgusting by-product of a respiratory infection, it’s a complex, functional tissue that serves a range of purposes, and in stingrays, it’s part of their armour.
Not only does it protect the ray from bacterial and blunt-object skin intrusions, but it also contains various immunity markers as well as toxins, which help protect and defend the animal, respectively.
There appear to be strong antimicrobial properties in the mucous, which is not only of interest to the stingrays but also has medical researchers’ ears pricked. 5
8. They’re a bit of a mystery
Despite all we know, this massive animal is relatively under-studied, and now that they’re endangered, we run the risk of sending them to extinction before we even know anything much about them.
They live in the murkiest of waters, spend most of their time hidden in the mud, and are generally shy animals, though it’s thought they are also likely very intelligent. 6
9. They’re being killed
Some communities hunt them on purpose for their meat and cartilage, others catch them by mistake and kill or maim them out of fear.
Their enormous size makes them a target of collectors and sports fishers, and their habitat is being destroyed.
In their native Mekong, damming has reduced viable habitats, and deforestation has led to various waterways problems, such as increased runoff and other pollution.
Throughout its range in Southeast Asia, this is a ray that’s in a lot of trouble, and the species is now listed as Endangered by the IUCN.
Giant Freshwater Stingray Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthes |
| Order: | Myliobatiformes |
| Family: | Dasyatidae |
| Genus: | Urogymnus |
| Species: | polylepis |
Fact Sources & References
- Author Name (Year), “Article Name”, Publication.
- Rikho Jerikho (2023), “Foreign stingers: South American freshwater river stingrays Potamotrygon spp. established in Indonesia”, scientific reports.
- Vidal Haddad Junior (2013), “Injuries by marine and freshwater stingrays: history, clinical aspects of the envenomations and current status of a neglected problem in Brazil”, BMC.
- Author Name (Year), “Article Name”, Publication.
- Guilherme Rabelo Coelho (2019), “Biochemical and biological characterization of the Hypanus americanus mucus: A perspective on stingray immunity and toxins”, NIH.
- “Giant freshwater stingray”, National Geographic.