A mysterious case of dying fish in the lower Congo River helped scientists discover that this body is the deepest river on the planet. It’s also a place where raging rapids, powerful currents and even submerged “waterfalls” divide the water, much as mountain ranges can separate habitats on land.
These impassable river barriers isolate fish populations and have shaped the emergence of hundreds of species, according to research presented on Dec. 12, 2019, here at the annual meeting of the American Geophysical Union (AGU).
Scientists’ first glimpse into the lower Congo’s depths began more than a decade ago, when they spotted pale, blind fish that appeared only when dying or dead. It turned out, those fish were killed by the bends, or decompression syndrome, in which air bubbles form in the blood and in body tissues.
In the researchers’ effort to understand how that was possible, researchers discovered that parts of the river bottom lay many hundreds of feet below the surface deeper than in any river on Earth.
Melanie Stiassny, a curator in the Department of Ichthyology at the American Museum of Natural History in New York City, studies the biodiversity and evolution of fish in the turbulent rapids of the lower Congo, the final 200-mile (322 kilometers) span before the river empties into the Atlantic Ocean in the Democratic Republic of Congo. Stiassny led the research investigating the puzzle of the dying fish.
More than 300 species of fish are found in the lower Congo alone, Stiassny said at the AGU meeting. The rapids there are so powerful that they physically separate fish populations, driving new species to evolve even when there isn’t much physical distance separating the animals from their close relatives.
Future US, Inc. 11 West 42nd Street, 15th Floor, New York, NY 10036.