Recently, a man surnamed Wang discovered a group of large, pitch-black, scaleless fish in Dalian’s Xishan Reservoir in Northeast China’s Liaoning Province. Photo: web

Recently, a man surnamed Wang discovered a group of large, pitch-black, scaleless fish in Dalian's Xishan Reservoir in Northeast China's Liaoning Province. Experts identified them as African catfish (Clarias gariepinus), likely released into the wild by humans. This highly adaptable invasive species competes with native fish for resources and may disrupt local ecosystem.

"There was a splashing sound on the water's surface, and when I looked closely, I saw a group of huge fish I'd never seen before," Wang noted. The fish were swimming in a school of at least six or seven, with the largest nearly a meter long, their dark bodies glistening under the sunlight.

Familiar with local fish species, Wang found these creatures unusual: "They were completely black, moved very fast, and-most strangely-had no scales." He managed to catch one, measuring over 50 centimeters in length and weighing around 2.5 to 3 kilograms. The fish had smooth, scaleless skin and multiple whisker-like barbels around its mouth.

After analyzing Wang's footage, Li Honglong, an associate researcher at the Dalian Natural History Museum, confirmed the species to be Clarias gariepinus, also known as the African catfish.

Native to inland waters across much of the African continent, the tropical and subtropical fish aggressively competes with native species for ecological niches and preys on a wide range of aquatic organisms, depleting natural resources. Remarkably resilient, it can survive out of water and even migrate between dried-up ponds in its native habitat, much like the climbing perch. Li believes the catfish in Xishan Reservoir were likely released by humans. While the species thrives in temperatures of 25 to 30 C and can tolerate a range of 7 to 38 C, it is unlikely to survive Dalian's winter naturally.