I’ve always thought of stingrays as saltwater animals, though I don’t have any particular reason to think this. But there are freshwater rays, and today’s animal also has the distinction of being the largest of the freshwater stingrays. It is unimaginatively called the giant freshwater stingray.

These animals are found rivers in southeast Asia; in Thailand, Malaysia, and Borneo. Giant freshwater rays tend to hang out at the bottom of rivers, and especially like muddy and sandy areas. They are sometimes found in estuaries, but there have been no reports of these stingrays in fully marine habitats.

A map of the distribution of the giant freshwater stingray. Image by Yzx, CC BY-SA 3.0, via Wikimedia Commons

As I mentioned, these stingrays get pretty big. Did I say pretty big? I meant huge. Giant, even. They can reach widths of almost two meters and lengths of five meters (though much of this is thanks to the rays’ long tails), and weigh in at 500-600 kg. The stingrays’ tails are equipped with a spine near the base. This spine measures over 35 cm long, making it the largest spine found on any stingray. Giant freshwater rays are coloured perfectly for a life on muddy river bottoms, being brown on top and light on the bottom.

Giant freshwater stingrays mainly rely on electric signals to sense and catch their prey, which mainly consist of small, bottom-dwelling fish and invertebrates, such as crustaceans and molluscs. The stingrays themselves have very few predators, thanks to their massive size. Even small stingrays are hard to hunt, thanks to their colouring and that stinger on their tails, which is covered in a toxic mucus.

A giant freshwater stingray in captivity. They tend to do quite poorly in aquaria, because it is difficult to provide them with adequate food and space. Image by Barry Rogge, CC BY 2.0, via Wikimedia Commons

Not a lot is known about reproduction in giant freshwater stingrays. It is believed that the rays find mates using the same electrical sensory organs that help them hunt. Once females have mated, they head into estuaries, which act as nursing grounds for the rays. They give birth to one to four live young, and care for them until they are ready to move into freshwater areas.

As is the case with most giant, interesting species, the freshwater stingray has suffered from population declines in recent years. They have been hunted for meat, aquaria and sport, and also are affected by habitat degradation. The giant freshwater ray is currently considered endangered, and thus far conservation programs have proved ineffective.

I have a mild fear of swimming in oceans, because I have an active imagination and can picture all the giant creatures swimming beneath me. I’ve always felt quite a bit safer in rivers and lakes, but after writing about some terrifyingly large freshwater critters, I’m not so sure. Maybe I should just avoid swimming altogether. Can you imagine one of these guys swimming up beside you as you take a leisurely dip in the Mekong? I think I would faint.

Cover image by BEDO (Thailand), CC BY-SA 4.0, via Wikimedia Commons