Don't Get Mekong

Saturday-Sunday, February 15-16, 2025

Don’t Get Mekong

Today’s special animal friend is the giant stingray, Urogymnus polylepis. Found in Southeast Asia and Borneo, it is the largest (heaviest) known freshwater fish in the world. The specimen found in the Mekong River in Cambodia on June 13, 2022, weighed 661 lbs. This exceeded the previous weight record for a freshwater fish — a giant catfish caught from the Mekong in 2005 — by 15 lbs. Two points: one, stay out of the Mekong, because two, it’s possible that there are larger catfish, larger stingrays, or both in there.

Catfish are omnivores, so they would eat you, but what about the 7-foot-wide, 13-foot-long (with the barbed tail) stingray? It will not eat you. Its small mouth has rounded teeth that are more like ridges, and it eats small fish and aquatic invertebrates. It is grayish brown on the back, like the river bottom on which it lives, and white with brown bands underneath. It is covered with brown mucus. This one is much smaller than the one caught on June 13:

Video on YouTube from AFP.

Like other rays, this species is viviparous. Females gestate one to four pups per litter, nourishing them with histotroph or “uterine milk,” a secretion produce by several ray and shark species. The pups are about a foot in diameter when they are born, typically in tidal estuaries. Jeremy from “River Monsters” catches a pregnant female in this 5-minute video:

The giant stingray’s sting is over a foot long, capable of piercing bone, and covered in toxic mucus. However, it is rare for humans to be stung.

The giant stingray is Endangered according to IUCN and Critically Endangered according to the government of Thailand. Overfishing is one of the threats. It is claimed that most are taken as by-catch by individual fisherman going after other species, but there is also a growing tourist presence trying to catch really big ones. Other threats include pollution, habitat fragmentation by dams, and collection for the aquarium trade.

Four very large rays, all of them female, were caught in the same general area in 2023. Dr. Zeb Hogan of the University of Nevada, Reno, believes that stretch of the river is a nursery area for females and pups. The great big one was released after receiving an acoustic tag that will last about a year, passing information about its movements to a recently installed array of 36 receivers. Dr. Hogan and his team hope to tag many more rays.

Dr. Hogan considers the identification of record-breaking large freshwater fish to be unexpectedly good signs for the health of their ecosystems.