River rays have always given me a sci-fi vibe.
Their silently hovering discs, with just the odd ripple or eye twitch to show something’s going on underneath, remind me of tiny little spaceships or cleaning bots. Brazil’s Xingu, with its beautiful “diamond”, or rare “eclipse” polkadots, even more so. But as with any futuristic tech, if handled clumsily it can be as dangerous as it is awesome.
Happy snoozing under the sands by day and crunching on crustaceans at night, the normally docile Xingu river ray belongs to the genus Potamotrygon, the most sting-happy rays of South America. Tipped with barbs, its tail can rip through flesh causing crippling pain and even tissue death (necrosis). Get stung too close to your vital organs, and you could be looking at actual death. It can regrow its stinger too, and not always one at a time, so occasionally you’ll find one packing double. But don’t worry, you can just grab some antivenom…oh.
Despite the common occurrence of stings – usually from species other than Xingu – stingray antivenom research is several agonising paces behind that of the spider and snake, so you’d be looking at anti-inflammatories, antibiotics, and maybe sticking the affected body part in hot water to help “deactivate” the venom. In severe cases, you won’t get it back again.
Xingu’s venom strength wanes with age, with the juveniles packing the most punch, but like many teenagers, guess where they like to hang around in summer? That’s right, by the shore. Not a happy combination.
However, it only really objects if you step on or harass it unnecessarily. This hasn’t stopped fishermen from hacking off Xingu’s stinger or killing it if hauled up as bycatch, so to lessen the pain for both sides, a push for local education and awareness is needed as well as the antivenom. Another duality: we seem to love it as much as we hate it.
Beautiful Xingu is a prized tank trophy. It’s banned from export, but captive bred rays occasionally pop up, as do illegally shipped ones, sometimes delightfully transported via PVC tube. Conservation wise it’s “Data Deficient”, which is never a good sign, and it’s restricted to the Xingu and Fresco rivers of the Amazon. Given that dams, sewage, and droughts due to El Niño are also stacked against it, its outlook isn’t great. At least it likes its babies – in the nice way for a change.
At up to 12 pups at a time, Xingu has larger litters than most river rays, and couldn’t decide over eggs or direct nourishment, so went with both: once the eggs hatch inside her, Mum feeds her babies with a milky substance. Females are slightly larger than males, and both have excellent eyesight as well as ampullae of Lorenzini – “shark nodes”– to detect small electrical fields in the murky depths.
So it’s not exactly bumping into us with its stinger, and to be fair, if I was cornered and poked by an alien, I’d respond appropriately too.
Latin: Potamotrygon leopoldi
What? Black river-dwelling stingray with bright starry spots.
Where? Brazil, endemic to the Amazon’s (shock!) Xingu River Basin.
How big? Up to 1.1 metre / 3.7 feet long.
Endangered? Currently listed as Data Deficient.
Probable motto: Please don’t annoy me, or we’ll both get hacked off.
They look beautiful. Do they need my help at all?
Restricted to a couple of the Amazon’s tributaries – and we all know how well that’s going – the Xingu could do with a bit more space.
International Rivers is campaigning against dams in parts of the Amazon, including another along the Xingu River.
WWF also looks out for the Amazon as a whole.
Just to prove I’m not fibbing:
“Freshwater stingray“. No date. Smithsonian’s National Zoo and Conservation Biology Institute.
Lameiras, Juliana Luiza Varjão et al. 2019. “Neotropical freshwater stingrays (Chondrichthyes – Potamotrygoninae): biology, general features and envenomation“. Toxin Reviews https://doi.org/10.1080/15569543.2018.1542406
“Polka-dot stingray: Potamotrygon leopoldi“. No date. Dallas World Aquarium.
“Potamotrygon leopoldi“. No date. FishBase.
“Potamotrygon leopoldi“. No date. IUCN Red List of Threatened Species.
“Potamotrygon leopoldi (Polka Dot Stingray, P13/14, P62)”. No date. Seriouslyfish.com.
Featured image credit: “Potamotrygon leopoldi“, by Mark Sabaj Pérez