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A zap from an electric eel acts like a natural Taser. It gives the creature the power to stop prey in its tracks. This gives the eel the upper hand - er, fin - that allows it to prevent dinner from swimming away. And that zap acts directly on the prey's nervous system, scientists now show.

But that's not all. This species ( Electrophorus electricus) can release different types of electric discharges, the new study finds. The eels, which hunt at night, sometimes send out just two or three short pulses. These cause nearby fish to twitch against their will. The eels detect those involuntary movements - which shows them where their dinner had been hiding.

That the eel may use electricity to scout for prey is "a remarkable finding," Mark Nelson told Science News. A biologist and eel researcher at the University of Illinois at Urbana-Champaign, Nelson did not work on the new study. The new finding, he says, "elevates the eel's strategy from a simple, reflexive stun-and-strike behavior to a more deliberative process." ( Deliberate, as a verb, means "to consider carefully.")

Better understanding of those zappers

Researchers have long been fascinated by the electric eel. This species can release bursts of electricity measuring up to 600 volts. That's enough to stop a fish cold in about three thousandths of a second. However, little research has been done on the details of how the eel's body reacts to that electricity.

Biologist Kenneth Catania, works at Vanderbilt University in Nashville, Tenn. He became curious about the eels' stun-gun action while studying high-speed videos of an attack, he told Science News.

For the new study, he put two unconscious fish in a tank with an electric eel. One prey fish had been treated with curare (ku-RAAR-ee). This substance prevented the fish's nerves from communicating with its muscles. The other fish was left untreated. Catania watched as the eel approached. When it sent out electric shocks, the fish that had not been treated with curare began to twitch. The curare-treated fish, however, never flinched.

That experiment told Catania that the eel's electricity must act on the nervous system, and not on the muscles themselves. (If the electricity affected the muscles directly, both fish would have twitched.)

Before a full shocking attack, these eels often emit very short bursts of electricity, just two or three quick zaps. The short zaps can make nearby fish twitch, too. Catania wondered if the eel used this process to hunt for hidden fish.

To find out, he conducted another experiment. He put an unconscious fish in a plastic bag in the tank. The plastic insulated the fish from the eel's electricity. He also added an electric device he could control inside the bag. The device would made the fish inside twitch on his command.

Then he unleashed the eel. It soon sent out short bursts of electricity. When the bag kept the fish from responding to those small pulses, the eel didn't follow up. But when Catania flipped the switch to make the fish twitch (and seemingly respond to the eel's zaps), the eel unleashed its full electric force. That convinced the scientist that the eel uses those short bursts to hunt down hidden prey. He published his findings December 5 in Science.

Biologist Jason Gallant at Michigan State University, in East Lansing, did not work on the new study. Electric organs have evolved at least six times in different species of fish, he notes. Gallant says he'd like to know if other electric predators also send out zaps to scout for prey.

Video of an electric eel hunting and catching a small fish (shown in speeds slower than life). In full-color sequences, knocklike sounds indicate electrical discharges from the eels. Black-and-white sequences have been colorized (red) to indicate when the eel is releasing electrical charges.
Credit: Images, video, and illustration: K. Catania/Vanderbilt University; Produced and narrated by Ashley Yeager Power Words
eel A fish with a snakelike body and no scales. Many migrate from freshwater to saltwater when it's time to spawn.

electricity A flow of charge, usually from the movement of negatively charged particles, called electrons.

involuntary An action that is not done intentionally.

muscle A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

nerves Long, delicate fibers that communicate across the body of an animal. An animal's backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold, and pain.

nervous system The network of nerve cells and fibers that transmits signals between parts of the body.

organ Various parts of an organism that perform one or more particular functions. For instance, an ovary makes eggs, the brain interprets nerve signals, and a plant's roots take in nutrients and moisture.

predator (adjective: predatory) A creature that preys on other animals for most or all of its food.

prey Animal species eaten by others.

TASER A brand-name version of a "conducted electrical weapon" used by police, the military, prisons, security guards, and others. It sends out electrodes that deliver a stunning discharge of electricity into a person to incapacitate them. Such devices are popularly referred to as stun guns.

unconscious Not aware of and not responding to one's surroundings; not awake.

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Electric eels get on their prey's nerves

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View the video A zap from an electric eel acts like a natural Taser. It gives the creature the power to stop prey in its tracks. This gives the eel the upper hand - er, fin - that allows it to prevent dinner from swimming away.

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Last summer, Alison Coulter got a big surprise as she piloted a boat along the Wabash River in Indiana. Coulter is a scientist at Purdue University in West Lafayette who studies fish called Asian carp. She was trolling the river to track the movements of these non-native fish. Here, the river teemed with the invasive carp. Startled by her boat's motor, a 60-centimeter (24-inch) carp leaped out of the river. The fish cleared the edge of the boat and whacked her right in the thigh.

Coulter got off easy. She sustained only a seven-centimeter bruise. In some cases, jumping Asian carp have broken a boater's nose, jaw or arm. These fish have even knocked some people unconscious.

The carp pose other dangers too. People have been introducing these fish, originally from Asia, into many new countries, including the United States. Once the carp reaches a new river or lake, the species multiplies quickly. These invaders also gobble a lot of food. Scientists worry that might threaten biodiversity, or the number of species living in a region. Many of the species left to starve might be native fish. If that happens, people who earn their living by angling for native fish might have trouble.

To better understand the threat, scientists need to learn more about Asian carp. Some researchers are investigating how far these invaders have spread. Another team is studying where the carp can reproduce. And still others are probing ways to block the fish from colonizing new rivers and lakes.

People will need to act fast to stop the carp from continuing to spread. "Once they get into an area, it's very difficult if not impossible to remove them," says Cory Suski. "And then you're stuck with them," explains this biologist at the University of Illinois at Urbana-Champaign.
Big eaters
Asian carp refers to several species. Two of them, the so-called bighead and silver carp, probably pose the biggest threats in American waters. Silver carp typically weigh up to 9 kilograms (20 pounds) and bighead carp weigh twice that much (although some bigheads have tipped the scales at a whopping 45 kilograms). A female can lay up to2 million eggs each year.

Bighead and silver carp are ravenous eaters. They swim with their mouths open, devouring algae, tiny aquatic animals called zooplankton and the eggs of other fish. "They'll eat just about anything," says Christopher Jerde. "If it's small and floating in the water, they'll eat it," explains this biologist at the University of Notre Dame in South Bend, Ind.

In the 1970s, people thought such voracious eating habits might come in handy. Perhaps the bighead and silver carp would remove excess algae from ponds on fish farms. So people brought the carp from Asia and released them into fish farms in the southern United States.

But the fish escaped.

The Asian carp spread northward into the Mississippi River Basin. This huge network of rivers and streams drains about 40 percent of the lower 48 U.S. states. The fish began eating a lot of the small organisms in the water. Meanwhile, native fish that also eat those organisms started to lose weight. In short order, the numbers of Asian carp exploded. In some areas, these non-native species became the most common fish.

People started to worry that the carp might reach the Great Lakes. Containing more than one-fifth of the world's surface fresh water, these five vast lakes straddle the border between the United States and Canada. Many native fish swim in those waters. If carp entered the Great Lakes, from there they could spread through connecting rivers and canals to even more of eastern North America.
DNA detectives
One possible pathway Asian carp could take into the Great Lakes is via a narrow canal passing through Chicago. It connects the Mississippi River Basin to Chicago's shoreline along Lake Michigan, one of those Great Lakes.

In 2002, people installed an electric barrier to keep invasive fish from swimming through this canal. The barrier creates an electric field that makes fish feel uncomfortable. When fish get too close to this field, they should turn and swim in the opposite direction.

But the truth is that no one really knew whether the electric barrier was blocking Asian carp. "Most people did not know where these fish were," explains Jerde.

One reason: Asian carp are hard to catch. So Jerde's team looked for a better way to detect them.

The researchers decided to search the water for carp DNA. DNA is a type of molecule found in all living things. Animals from the same species have similar DNA. If Asian carp were present, they would shed scales and mucous containing their DNA. Their poop contains DNA as well. By testing the water, scientists might be able to find evidence of Asian carp, even without observing the fish directly.

In 2009 and 2010, Jerde's team collected water samples along the Chicago canal and in other waterways in and near Chicago. They looked for evidence of Asian carp DNA. And, recalls Jerde, "We found their DNA in a lot of places nobody wanted to see it."

It was upstream of the canal's electric barrier. It turned up in waterways very close to Lake Michigan. The DNA even showed up in one part of the lake. The findings made Jerde feel "sick." It was the last thing he had wanted to find.

And it got worse. In 2011, Jerde's team identified Asian carp DNA in a second Great Lake: Erie. But tests of many other rivers and streams connected to Lake Michigan outside of the Chicago area came back negative. "The good news," says Jerde: The DNA suggests these fish are not yet everywhere. Still, alien carp DNA in two of the Great Lakes is troubling. "It's a red flag," he says.
Egg hunt
Asian carp will spread and readily colonize a new region if they can reproduce in many types of rivers. These fish reproduce by spawning. A male releases sperm into the water. These reproductive cells can fertilize eggs deposited by a female fish. Over time, the fertilized eggs will float down a river and hatch.

Coulter wanted to find out whether Asian carp were particular about the water conditions needed to spawn. In Asia, these fish usually spawn in big rivers. Coulter wanted to probe whether that was true in the United States as well.

So she and her colleagues traveled down the Wabash River in Indiana by boat in 2011 and 2012. This river is part of the Mississippi River Basin. After netting eggs, the researchers brought them into the lab for identification.

To their surprise, the biologists found Asian carp eggs even in a narrow, shallow part of the river. That means the fish can reproduce in more places than scientists had previously thought possible. And the fish spawned over an extended period - from May through September. Being adaptable makes them an especially successful invader, Coulter concludes.

She is now studying how far and fast these carp swim. She's also investigating whether their movements depend on temperature or the flow of the river. Knowing such details could help scientists predict where the carp will turn up next.

Researchers at the U.S. Geological Survey have studied whether Asian carp could successfully reproduce if they become more common in the Great Lakes. The fish will need to spawn in nearby rivers. A study published in June 2013 now indicates that four rivers connected to the Great Lakes have the right water conditions for Asian carp eggs to develop and hatch.
Keep out!
Scientists know that Asian carp are on the move. Can they be stopped?

An electric barrier isn't foolproof. For example, fish might shield themselves from the electric field by swimming alongside barges, a type of boat. Suski, the scientist at the University of Illinois at Urbana-Champaign, wanted to come up with a second line of defense.

His team wondered whether carbon dioxide, a gas, might block the carp. Fish can sense carbon dioxide (CO ₂) in the water. If CO ₂ levels get too high, fish might find it hard to breathe and swim away. So Suski wondered: "Do fish get grumpy when you expose them to CO ₂?"

In experiments conducted in 2010 and 2011, the Illinois researchers placed bighead and silver carp into small containers. Then the experts added varying amounts of CO ₂ to the water and observed the fish. At higher CO ₂ levels, bighead carp breathed more slowly and gulped for air at the surface. And the silver carp all passed out, rolled on their backs and floated.

In a second test, the fish got a choice. Researchers put individual silver carp into one chamber that was connected to a second. Then they began adding CO ₂ to the first chamber. Most fish fled into the second chamber.

The findings suggest that pumping CO ₂ into the water might help keep Asian carp away, says Suski. But if the gas spreads into the rest of the river, it might perturb the behavior of native fish as well. So Suski's team is working on ways to confine the added CO ₂ to just one part of a river.

By learning more about Asian carp, Suski and other scientists hope to keep the fish from wreaking havoc on native animals. If carp and other invasive species spread unchecked, says Jerde, the environment that people see today "may not be the same environment they have 10 years from now."
Power Words
algae A large group of mostly photosynthetic organisms, meaning they use light and carbon dioxide to make sugar and oxygen. Algae range from long seaweeds to single-celled microorganisms.

Asian carp Several species of fish native to Asia. Several have been introduced to many new countries, including the United States. The term covers bighead, silver, grass and black carp.

bighead carp A species of Asian carp that can weigh up to 45 kilograms (100 pounds). Bighead carp eat small organisms such as zooplankton.

carbon dioxide A gas (CO ₂) made of one carbon atom and two oxygen atoms.

DNA A long, spiral-shaped molecule that carries genetic information. DNA can be found inside nearly every cell of an organism.

invasive species A non-native species whose introduction may cause ecological and economic damage.

native An individual or species that grew up or evolved in a particular region of the world. Invasive species are non-native organisms and often thrive in a new region because they have escaped the natural predators that kept their numbers in check.

silver carp A species of Asian carp that usually weighs up to 27 kilograms (60 pounds). Silver carp can jump high out of the water when startled by the vibration of boat motors.

spawn To release or deposit eggs.

sperm A male reproductive cell.

zooplankton Tiny floating animals in the water that feed on single-celled plants and plantlike organisms.
Word Find (click here to print puzzle)

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Last summer, Alison Coulter got a big surprise as she piloted a boat along the Wabash River in Indiana. Startled by her boat's motor, a 60-centimeter (24-inch) carp leaped out of the river. In some cases, jumping Asian carp have broken a boater's nose, jaw or arm.

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When things die, nature breaks them down through a process we know as rot. Without it, none of us would be here. Now, scientists are trying to better understand it so that they can use rot — preserving its role in feeding all living things.

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Fighting big farm pollution with a tiny plant

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Fertilizer runoff can fuel the growth of toxic algae nearby lakes. A teen decided to harness a tiny plant to sop up that fertilizer.

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Water sensor quickly detects algal poison

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A new sensor can detect poisons from harmful algae within minutes so that drinking-water plants can start timely treatments.

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Ocean of the future may make shrimp small and colorful

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Carbon dioxide released into the air can end up in the ocean, making it more acidic. A teen showed that this acidification could shrink shrimp and make them more colorful.

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SAN JOSE, Calif. - Many people like milk. But Glenn Grimmett, 13, truly loves it. He downs around 1.9 liters (a half gallon) every day. So this teen at the Weiss School in Jupiter, Fla., was understandably upset when he learned that bad things sometimes taint that milk - such as dangerous chemicals from fungi and drugs used to kill bacteria. Then he designed a science fair project to probe for pollutants in his milk. And he found several.

Glenn showed off the results of his dairy investigation at an event known as Broadcom MASTERS (for Math, Applied Science, Technology and Engineering for Rising Stars). The competition brings together students with winning middle-school science-fair projects from across the United States. Finalists shared their work with each other and the public here on October 3. This annual science program was created by Society for Science & the Public. It's sponsored by Broadcom, a company that builds devices to help computers connect to the Internet.

Cow's milk contains many proteins and vitamins. But it also can include things such as added hormones and other chemicals fed to the cows. Such additives can help cows grow quickly and produce more milk. However, these chemicals can end up in the milk we drink. Milk also can pick up chemicals from a cow's feed. Glenn was especially concerned about two of them - aflatoxin M1 and antibiotics.

Aflatoxin M1 is a toxin produced by the fungus Aspergillus. That fungus can grow on many crops, including both peanuts and the grain that's fed to cows. The toxin is a known carcinogen, or substance that can cause cancer. In the United States, milk is tested for aflatoxin M1. It is illegal to sell milk containing this toxin at levels higher than 0.5 parts per billion - or one aflatoxin molecule per two billion molecules of milk.

Antibiotics are drugs used to kill germs. Many farmers give them to their cattle to help prevent disease. By keeping livestock healthy, antibiotics also can help animals grow faster. But the Food and Drug Administration places limits on the how much of these drugs can be present in milk sold in the United States.

Glenn wanted to find out if there were antibiotics or aflatoxin M1 in milk. So he went to local grocery stores and bought 25 different brands of milk. Then he ran a test called an ELISA, which stands for enzyme-linked immunosorbent assay. It can detect very small amounts of chemicals in a liquid.

ELISA tests come in kits, with all the solutions you need. Glenn got his by calling up Abraxis, a company that makes a type he wanted to use. "I contacted the CEO," he says, which is the man who heads that company. "He allowed me to rent some of his equipment," Glenn says. "He also let me rent ELISA test kits."

Says Glenn, "I did my testing at home in my bathroom because it's well ventilated." For safety, the teen wore safety glasses, protective gloves and a lab coat. When he finished, "I returned all the chemicals to the company that gave it to me," he notes.

He searched for aflatoxin M1 and two antibiotics - tetracycline (Teh-trah-SY-kleen) and sulfamethazine (SUL-fa-METH-uh-zeen).

Glenn found that 42 percent of his milk samples contained some aflatoxin. Amounts were quite low, below 0.5 parts per billion. The European Union has even tougher standards, permitting even less of the toxin. All but one milk sample met the European standard as well.

More concerning to Glenn, 14 of his 25 milk samples contained small amounts of sulfamethazine, and five contained tetracycline. Low amounts of antibiotics, over long periods of time, can lead to resistance- as bacteria evolve to fight off the drugs we use to kill them.

Most milk is tested for these drugs. Milk with more than 30 parts per billion of sulfamethazine or 300 parts per billion of tetracycline can't be sold. Glenn would prefer that milk contain no antibiotics at all. His test is much more sensitive than the tests generally used, and could detect even trace amounts of the drugs. The teen argues that the milk industry needs a test that is more sensitive than it has now but is still quick, easy and reliable. "It needs to be able to test four million tankers each year," he notes. Someday, Glenn hopes that routine milk tests will detect even trace levels of antibiotics and help to keep them out of his favorite drink.

Power Words

aflatoxin These are chemicals produced by the fungi belonging to the genus Aspergillus. They can cause cancer in humans and diseases in animals such as turkeys. Because they grow on grain and nut crops, they can get into food, including cow's milk.

antibiotic A germ-killing substance prescribed as a medicine (or sometimes as a feed additive to promote the growth of livestock). It does not work against viruses.

antibody Any of a large number of proteins that the body produces as part of its immune response. Antibodies neutralize, tag or destroy viruses, bacteria and other foreign substances in the blood.

Aspergillus A genus of fungi which grows on grains, nuts and seeds. It produces a group of chemicals - called aflatoxins - which can cause cancer.

carcinogen A substance, compound or other agent (such as radiation) that causes cancer.

CEO An acronym for Chief Executive Office, which is typically the person who runs a company.

dairy Containing milk or having to do with milk. Or a building or company in which milk is prepared for distribution and sale.

ELISA (or enzyme-linked immunosorbent assay) This is a test used to detect very small amounts of chemicals in a liquid.

enzymes Molecules made by living things to speed up chemical reactions.

European Union The confederation of 28 European countries that have agreed to work peacefully together. Residents of EU can move freely between its member countries and sell goods to them. Most members have also adopted the same currency, known as the Euro.

Food and Drug Administration (or FDA) A part of the U.S. Department of Health and Human Services, FDA is charged with overseeing the safety of many products. For instance, it is responsible for making sure drugs are properly labeled, safe and effective; that cosmetics and food supplements are safe and properly labeled; and that tobacco products are regulated.

fungus ( plural: fungi) One of a group of single- or multiple-celled organisms that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.

hormone (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.

parts per million (billion or trillion) Frequently abbreviated as ppm (or ppb or ppt), it is a measure of the number of units of some material that it mixed into another. The units should be the same (or equivalent) for both materials. The term is used to describing extremely small concentrations of one chemical dissolved in another. For example, a solution of 300 parts per billion of sodium in water would mean that there are 300 sodium atoms for every billion water molecules.

proteins Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins.Medicines frequently work by latching onto proteins.

resistance (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection.

Society for Science and the Public (or SSP) A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: The Intel Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

solution A liquid in which one chemical has been dissolved into another.

standards (in research) The values or materials used as benchmarks against which other things can be compared. For instance, clocks attempt to match the official standard benchmark of time - the second, as calculated by the official atomic clock. Similarly, scientists look to identify a chemical by matching its properties against a known standard for a particular chemical. (in regulations) A limit above which something may not be used, sold or considered safe.

sulfamethazine A type of antibiotic, which is a chemical that can kill bacteria.

tetracycline A type of antibiotic, which is a chemical that can kill bacteria.

ventilation (v. ventilate) The movement of fresh air into a room or processes that move air around and between different rooms.

vitamin Any of a group of chemicals that are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be made by the body.

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SAN JOSE, Calif. - Many people like milk. But Glenn Grimmett, 13, truly loves it. He downs around 1.9 liters (a half gallon) every day. So this teen at the Weiss School in Jupiter, Fla., was understandably upset when he learned that bad things sometimes taint that milk - such as dangerous chemicals from fungi and drugs used to kill bacteria.

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Fattening maggots to create a designer food

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Davia Allen wants to reduce food waste by feeding it to fly larvae - which can then serve as food for poultry, fish and people.

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Teen develops water-saving pods for seeds

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In California's drought, every drop of water counts. A teen developed a capsule to keep sprouting seeds wet and reduce water use.