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Rough waters: one of the world's most turbulent rivers is home to a wide array of fish species. Now, large dams are threatening their future.

For most of its length, Africa's Congo River is calm. The continent's largest river slowly meanders over a high, flat plateau, collecting water from 3.6 million square kilometers (1.4 million square miles) of land. Near the cities of Kinshasa and Brazzaville, the water forms a large pool. Then, the water plunges off the plateau to form the lower Congo River.

Over the next 350 km (217 mi), the water descends more than 280 meters (918 feet) to reach the Atlantic Ocean. This extreme drop in height combined with the huge amount of water in the river creates powerful currents. "The largest rapids on Earth are found in the lower Congo," says Melanie Stiassny, an ichthyologist at the American Museum of Natural History in New York. Stiassny studies the fish that live in these wild waters.

FISH STOCK

The violent rapids make studying much of the lower Congo tough. Only a few areas have calm enough water to travel by boat, so Stiassny gets help from world-class river kayakers. They travel with instruments on their boats to collect data such as the water's speed and depth. Even these expert boaters can safely ride on only a small portion of the river--the rest is too dangerous.

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The lower Congo has one of the most diverse fish populations in the world. More than 300 species of fish are found in this small stretch of river. In a similarly long portion of the Mississippi River, you would be lucky to find 20 fish species.

Roughly 80 of the fish species found in the lower Congo River are endemic, or found no place else. One such species is Lamprologus lethops. Stiassny thinks this blind fish lives in river canyons as deep as 160 m (525 ft) below the surface.

WALL OF WATER

Stiassny has discovered that the diversity of fish in the lower Congo is likely the result of the river's extreme conditions. She has been analyzing the DNA (chemical that carries hereditary information) of different fish populations in the river.

Members of a single species of fish should have similar DNA. However, Stiassny has found significant differences in the DNA of individuals of the same species living in different areas. In one case, individuals living on one side of the river had significantly different DNA than that of the same species living on the opposite side.

Stiassny thinks that the river's powerful currents are acting as a natural barrier for the fish. They can't swim across the currents to interact and mate with one another. "The genetics have diverged so much that we can say there is no connection between the two populations," says Stiassny. Over time, the separation might cause populations of the same species to develop new characteristics and become different species.

PROTECTING THE RIVER

Many of the unique fish that live in the river may soon be at risk of disappearing. Two hydroelectric dams have been built already on the lower Congo River to generate energy, mostly for mining. There are plans to build an even larger dam. "That could be the end of the ecosystem as we know it," says Stiassny.

She hopes the information she has been gathering will be used to make predictions about how different dam designs might affect the river. That information could be used to create a dam that preserves important fish habitat.

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check it out

Most fish that you see--from pouting goldfish to iced salmon--are among the roughly 30,000 species of ray-finned fish. Fish make up more than hall of all known vertebrates, or animals with a backbone, and live in most waters of the world. To find out more information about fish and their adaptations to water, check out the Milstein Family Hall of Ocean Life at the American Museum of Natural History, ask your teacher, or go to www.amnh.org.

web extra

For more information about fish and a video interview with Stiassny, visit: www.scholastic.com/scienceworld

Rough Waters

PRE-READING PROMPTS:

* Do you know where the Congo River is?

* Africa's Congo River has one of the most diverse fish populations of any river on Earth. What do you think created this exceptional diversity?

* What human activities do you think could be threatening the Congo River's habitat?

DID YOU KNOW?

* The Congo River is Africa's most powerful river and Earth's second largest river by volume, after the Amazon River in South America. The Congo River drains a basin of 3.68 million square kilometers (1.42 million square miles).

* At 4,700 km (2,920 mi) in length, the Congo is the eighth longest river in the world and the second longest river in Africa (after the Nile).

* The Congo River drains water from both the Northern and Southern Hemispheres and crosses the equator twice. This unique route causes the river's volume to be relatively stable throughout the year because some part of its watershed is always in a rainy zone.

CRITICAL THINKING:

* The Congo River has the potential to be a rich source of hydroelectric power for West Central Africa. It also is a transportation and communication resource for large areas not served by roads. How do you think the people and governments of the countries surrounding the Congo River balance their needs for power and transportation with the need to protect the river's incredible diversity of plant and animal life?

CROSS-CURRICULAR CONNECTIONS:

LANGUAGE ARTS: When Melanie Stiassny studies the Congo River, she enlists the help of world-class kayakers that navigate the rough waters. Have students write a short story about what it is like to brave those rapids in search of the special fish that Stiassny researches.

RESOURCES

* Take a look at the American Museum of Natural History's animation of land-cover mapping of the Congo River using satellites and computers: www.amnh.org/sciencebulletins/bio/vlcongoriver.20060601.

* Check out the nonprofit group International River's fact sheet about the proposed hydroelectric dams on the Congo River. www.internationalrivers.org/en/node/345.

* Watch clips from National Geographic's Explorer episode about the bizarre fish of the lower Congo at their Web site: http://channel.nationalgeographic.com/series/explorer/3826/Overview.

DIRECTIONS: Match the word in the left column with the correct phrase in tile right column.
-- 1. ichthyologist   a. belonging exclusively to a certain place;
                     found no place else

-- 2. endemic         b. animals with a backbone

-- 3. hydroelectric   c. scientist who studies fish

-- 4. vertebrates     d. having to do with the generation of
                     electricity from the energy of falling water


ANSWER

Rough Waters

1. c 2. a 3. d 4. b
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Title Annotation:EARTH: RIVERS
Author:Norlander, Britt
Publication:Science World
Geographic Code:60AFR
Date:Apr 20, 2009
Words:1097
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