October 28, 2019

In September, scientists from the National Museum of Natural History at the Smithsonian Institution in Washington, D.C., announced the discovery of a new type of electric eel that has the strongest shock of all bioelectric animals: Electrophorus voltai. A native of South America’s Amazon River, E. voltai generates a powerful 860 volts, more than seven times the voltage of a typical American wall socket (120 volts). The eel is named after Alessandro Volta, the Italian physicist who invented the battery.

Electrophorus voltai, seen here, is one of two new electric eel species recently discovered in the Amazon. Credit: © L. Sousa

From 2014 to 2017, the Smithsonian team studied Amazonian electric eels with researchers from Brazil’s University of São Paulo. They tested the eels’ voltages and studied their muscle structures, body shapes, and DNA. To their surprise, the Amazon electric eel—long thought to be a single species, Electrophorus electricus—turned out to be three distinct species. E. electricus remained as the main type, but the team named E. voltai and another electric eel, Electrophorus varii, as new species. The three species differ in voltage as well as in head shape, sense organs, and distribution. E. electricus lives in northern Amazon basin waters, while E. voltai inhabits waters further south. E. varii swims among the slow-flowing lowland Amazon basin waters.

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The Amazon River, the world’s second longest river, is 4,000 miles (6,437 kilometers) long. Credit: WORLD BOOK map

The new findings reemphasize the incredible diversity of the Amazon River and rain forest, much of which is still unknown to science, as well as the importance of conservation and saving the region from deforestation, logging, and fires.

The electric eel stuns its enemies and prey with a powerful electric shock. The electricity-producing organs take up most of the body. The other inner organs lie just behind the head. Credit: © Andre Seale, Alamy Images

Electric eels are a long, narrow fish that produce strong electric discharges, or shocks. The animals are not true eels, but rather a type of knifefish.  An electric eel discharge can kill a fish and stun such potential predators as caimans (large reptiles) or humans. However, electric eels rarely harm people in the wild.

March 7, 2017

Off the coast of Brazil, where the Amazon River spills into the Atlantic Ocean, scientists are taking the first up-close and personal look at the recently discovered Amazon Reef. Existence of the large coral reef was not confirmed until an oceanographic survey of the area in 2012. The survey’s findings were published in 2016, and in late January 2017, scientists began exploring the reef two-by-two in a small submarine, the exploration craft of the Greenpeace ship Esperanza.

The Greenpeace ship Esperanza recovers its two-person research submarine from a dive to the Amazon Reef in February 2017. Scientists are just beginning to explore the recently discovered reef off the coast of Brazil. Credit: © Marizilda Cruppe, Greenpeace

In the late 1950’s, a ship collected sponges—animals that often inhabit coral reefs—from the floor of the Amazon Delta. Because of the area’s oxygen-poor, murky-brown mix of freshwater and ocean saltwater, however, the possibility of a reef there was largely discounted. Coral reefs typically grow in clear saltwater that allows enough sunlight to support photosynthesis in their algae and plants. Photosynthesis is the process in which organisms use energy from sunlight to make food. In the following decades, colorful reef fish were spotted in the same part of the Amazon Delta, and speculation grew that a reef existed beneath the waves.

Fish swim above the corals and sponges of the Amazon Reef off the coast of Brazil. This photograph is one of the first taken from a submarine launched by the Greenpeace ship Esperanza. Credit: © Greenpeace

Finally, in 2012, a team of oceanographers led by Rodrigo Moura of the Federal University of Rio de Janeiro, began studying the Amazon Delta’s sea floor. Using acoustic sampling, the researchers mapped the area, and subsequent dredging brought corals, sponges, and other reef species to the surface, proving the reef’s existence. After further study, the team published its findings in the journal Science Advances in April 2016.

The Amazon Reef stretches 600 miles (970 kilometers) along the Brazilian coast and covers an area of 3,600 square miles (9,300 square kilometers) with a depth range of 100 to 400 feet (30 to 120 meters). Since their first dive in late January 2017, oceanographers have turned the submarine’s lights on a wide variety of sea life, including three new fish species, rare manatees, yellow-spotted river turtles, and giant river otters. Given the Amazon Reef’s singular nature as the only known reef at the mouth of a major river, it may harbor many more undiscovered animals or plants as well. Further dives will help scientists learn how the reef functions and further define the ecology of the vast Amazon River Basin.

At a time when most reef systems are rapidly declining because of overfishing, pollution, and climate change, the discovery of a thriving reef in an unlikely place is encouraging. The reef is likely already in trouble, however, as oil companies are scouting the area and preparing to drill for oil. Drilling could severely harm the reef, as could any oil leaked into the delta waters.

February 17, 2017

Earlier in February, scientists learned that the dorado catfish (also known as the dourada or gilded catfish) of South America has the longest migration of any freshwater fish. These large catfish live in the Amazon River Basin, and their migratory path takes them from the foothills of the Andes Mountains to the mouth of the Amazon River on the Atlantic Ocean, and then back again—a trip of more than 7,200 miles (11,600 kilometers)!

The long-traveling dorado catfish navigates the waters of the Amazon River Basin throughout its life. Credit: © Michael Goulding, Wildlife Conservation Society

Catfish have pairs of fleshy whiskerlike growths near the mouth. These growths, called barbels, resemble the whiskers of a cat. Catfish differ from most other fish in that they do not have scales. Catfish live in many different places around the world, and they come in a variety of shapes and sizes. The dorado catfish (Brachyplatystoma rousseauxii) is just one of several different species (kinds) of catfish that live in the Amazon River and its many tributaries. Dorados can grow beyond 6 feet (2 meters) in length and are grouped with other “goliath” catfish, so named because of their large proportions. Their lengthy migration has long been suspected, but only recently have the details of their epic migratory journey been confirmed. A study of the distribution of larvae, juveniles, and mature dorados showed where the fish tend to be at different stages of life. The study, published in the journal Scientific Reports, was a group effort led by the Wildlife Conservation Society’s Amazon Waters Initiative. Ronaldo Barthem from the Museu Paraense Emílio Goeldi in Brazil led the research team.

This map shows the remarkable migration of the dorado catfish through the Amazon River Basin. Credit: © Wildlife Conservation Society

Barthem and his team found that dorados spawn in the Andes waters of Colombia, Ecuador, Peru, and Bolivia. The larvae then begin a precarious journey downriver, finding their way through such tributaries as the Madeira, the Marañón, and the Rio Negro—all major rivers themselves—to the mighty Amazon itself. The young catfish grow as they travel eastward, following the currents across Brazil to the eventual end of the Amazon north of Marajó Island on the Atlantic coast. There the fish gather in the vast and organically rich waters of the estuary, feeding, growing, and maturing. After a couple years, the fish get the urge to travel back upriver, taking the long swim—another two years—back to the spawning grounds where the life cycle begins again.

Dorados also live in the rivers of Guyana and Venezuela, and they are an important food fish for people throughout the Amazon Basin. Dorado catfish are not an endangered species, but their migration becomes increasingly difficult each year because of damming, deforestation, mining, and pollution.

Salmon and eels are other fish known for their long migrations, but their routes combine saltwater and freshwater routes and still fall short of the long swim of el dorado.