Tiny Fish Climb 50-Foot Waterfall

Democratic Republic of Congo —(Map)

Scientists have reported a surprising sight in the Democratic Republic of Congo – thousands of tiny fish climbing UP a tall waterfall. The fish use special fins to climb the rock wall behind the waterfall. The scientists say knowing about the unusual activity may be important for protecting the fish.

Shellears are small freshwater fish, about the size of a person’s little finger. About 17 years ago, a scientist from the University of Lubumbashi noticed thousands of these fish climbing the Luvilombo waterfall. He even filmed the fish climbing, but he later lost the video.

But his reports of the climbing fish got the attention of another researcher – Pacifique Kiwele Mutambala. Mr. Mutambala decided to go to Luvilombo Falls to see if he could confirm the story of the climbing fish. Fish have been known to climb waterfalls on other continents, but it had never been reported in Africa before.

Mr. Mutambala went to Luvilombo Falls during the rainy seasons of 2018 and 2020. What he saw amazed him. Small fish were clinging to the rock behind the falling water, making their way up the 50-foot (15-meter) waterfall. “I was very excited,” he said.

The scientists studied the fish. They learned that the shellears climb by pushing up with their back fins and using their front fins to grab onto the rock. The front fins have tiny hooks which help the fish to hold on to the stone. The fish move their bodies quickly, in a motion that’s almost like swimming straight up.

The fish don’t try to climb in the middle of the waterfall where the water is strongest; instead, they stay in the “splash zone” on the edges of the falls.

The climb is hard work, and the fish rest often by clinging to a flat spot on the rock. Sometimes they have to hang upside down under an overhang. In all, it takes about 10 hours for a fish to make the climb.

Sometimes the fish fall off and have to start again. The researchers point out that not all shellears can make the trip. Only the smaller, younger fish can climb up. Once the fish grow larger than about two inches (5 centimeters), they become too heavy to carry their own weight up the waterfall.

It’s still not clear why the fish climb up. They may be looking for food, or hoping to avoid predators. They may simply be trying to return home after being washed down by flood waters.

In any case, the discovery is an important reminder that animals often do things that humans don’t expect. As one scientist put it, “If you would ask a regular person, do you think fish can climb falls, most of them will tell you: you are crazy.”

The scientists say understanding the fish’s behavior is important for protecting them. Migrating fish like shellears depend on the river. If the water is lost to irrigation or a dam, it could cause serious problems for the fish. Said one scientist, “If there is no water, there are no fish.”