Catching ‘Dory’ fish can poison entire coral reef ecosystems | Science News for Students

Catching ‘Dory’ fish can poison entire coral reef ecosystems

Blue tangs and other popular saltwater-aquarium fish often are caught using cyanide
Jun 17, 2016 — 1:48 pm EST
blue tang

Every “Dory” sold in shops was caught from the wild. And there’s a high likelihood it was caught using a dangerous poison, new research shows.

Stéphane Duquesne/Flickr (CC-BY-NC 2.0)

The popularity of animated kids’ movies — Finding Nemo and its new sequel, Finding Dory — could spell doom for many coral reef communities, a new study warns. But even without families trying to bring home the types of fish portrayed in these films, coral-reef species are in trouble. The aquarium industry has been harvesting fish as pets. And more than half of the saltwater fish sold as U.S. pets may have been caught with a deadly poison — cyanide. That is the finding of a new study.

Many kids fell in love with orange-and-white clownfish after watching the 2003 classic Finding Nemo. Its namesake was one of these fish. Owing to the movie’s popularity, many parents bought kids their own Nemo. People purchased so many Nemos that some wild communities of the fish plummeted in number.

Now there are worries that a new movie out this week, Finding Dory, may have a similar effect on Dory’s species, the blue tang.

clownfishToday, it is possible to buy a clownfish that has been bred in captivity. That has taken pressure off wild populations of the fish. But no one has been able to do this successfully for blue tangs. So every blue tang that is sold in a shop has to come from the wild. A surprisingly large number of those fish are captured using cyanide, new research shows.

For those who supply pet-shop fish, cyanide is “cheap and easy” wayto catch them, notes Craig Downs. He directs the Haereticus Environmental Laboratory in Clifford, Va. A diver simply adds a pellet of cyanide to a bottle and squirts a bit on a target fish. Or someone may pump larger quantities down from a boat. The poison quickly stuns the fish, Downs explains. It then can be captured and later sold.

But cyanide is deadly. Coral exposed to cyanide can bleach and die. Non-targeted fish and other organisms left behind also can die. Even the fish caught for sale in pet shops may die within a few weeks or months after the cyanide treatment.

“If you survive [exposure], you’re messed up for the rest of your life,” Downs says. There are laws that should prevent divers from using the cyanide-stun method to capture fish. And animals caught this way are not supposed to be allowed into the United States for sale. But “this practice happens all through the Indo-Pacific,” says Downs. (That’s a term for waters of the Indian and Pacific Oceans.) As many as 30 million fish may be caught this way every year, Downs says. Of those, some 27 million may die.

How they know cyanide had been used

There is no way for someone purchasing a fish in a pet store to tell if the animal had been exposed to cyanide. “You have to be a fish pathologist” to see the signs, Downs says. But after being exposed to the poison, a fish’s body turns it into another chemical. This is thiocyanate (THY-oh-SY-uh-nayt). The fish will excrete the new chemical in its urine. Experts can detect residues of the thiocyanate in the water.

Downs works with Rene Umberger. She is director of For the Fishes. This conservation group works to protect fish and coral reefs from the aquarium trade. Recently, the pair wanted to get an idea of how many of the fish sold in pet stores may have been caught using cyanide. They purchased 89 fish from shops in California, Hawaii, Maryland, North Carolina and Virginia. Then they collected samples of the water in which each fish had been swimming. This water contained the fish’s pee.

green chromisThe pair sent their samples off to an independent laboratory. More than half of the fish had been exposed to cyanide, the lab tests showed. These included many of the blue tangs — or Dorys. The green chromis, another popular (though less movie-famous) fish, tested positive for the chemical at an even higher rate.

The pair also obtained some fish from companies that breed fish in captivity. (In other words, these fish were never in the wild.) None of those fish excreted thiocyanate. This confirms that only wild-caught fish had been exposed to cyanide.

The researchers will present these results later this month at the International Coral Reef Symposium in Hawaii.

Cyanide stunning is very common

Most of the 11 million saltwater fish sold in the U.S. aquarium trade come from coral reefs in the Indo-Pacific. In some places, such as Hawaii and Australia, there are laws about catching these fish. These countries can be quite protective of the environment. And there often is good government enforcement of their laws. As a result, their local fish can be collected without too much harm.

But in many places, few laws exist. Or there may not be enough enforcers to police those laws (or ensure that they are followed). In these places, fish collectors may use quick, inexpensive — but very destructive — practices, such as cyanide.

A 2008 report by the National Oceanic and Atmospheric Administration estimated that 90 percent of the saltwater aquarium fish imported into the United States had been captured with cyanide or other illegal methods. Downs suspects that the true numbers for his fish are higher than he and his colleague are now reporting.

Here’s why. Fish excrete detectable levels of thiocyanate for only a short time. So if their pee is not tested quickly enough, any evidence that they had been poisoned might disappear.

And there’s another sign that his team's new data may underestimate cyanide exposures in imported fish. Downs’ team has developed a new, more sensitive method for detecting cyanide exposure. The initial results using it, Downs says, show that many more fish may have been exposed than the first method that he had used showed.

Buying Dory — blue tangs — was never a good idea. The fish come from the wild. And they require a lot of upkeep. But the new evidence shows that the way these fish are caught harms not only them but also the coral reefs in which they had lived.

Still, this doesn’t mean that people should stop buying all saltwater fish, Downs says. “If consumers really want to have coral-reef fish, then [try] going the cultured route,” Downs says. By cultured, he means seek out fish that had been raised in captivity — not collected in the wild.

More than 1,800 species enter the U.S. aquarium trade each year. Only around 40 are captive-bred. That may not be many, but identifying them is easy. Umberger’s group released a free app for Apple devices called Tank Watch. This app lists them all. The app doesn’t list every species that may be in a store. But if a species isn’t on the good list, buyers can assume it is coming from the wild using a harmful technique.

Better yet, Downs argues, is simply to travel to where these fish live and “visit the fish there.”

Power Words

(for more about Power Words, click here)

bleach    A dilute form of the liquid, sodium hypochlorite, that is used around the home to lighten and brighten fabrics, to remove stains or to kill germs. Or it can mean to lighten something permanently, such as: Being in constant sunlight bleached most of the rich coloring out of the window drapes. This term also can apply to coral reefs. It describes what happens when coral expel the algae that live in them. This causes the coral to turn white. And it can lead to coral death.

breed    (noun) Animals within the same species that are so genetically similar that they produce reliable and characteristic traits. German shepherds and dachshunds, for instance, are examples of dog breeds. (verb) To produce offspring through reproduction.

chemical    A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

coral   Marine animals that often produce a hard and stony exoskeleton and tend to live on the exoskeletons of dead corals, called reefs.

cyanide    Any chemical compound containing a pairing of carbon and nitrogen, but especially sodium cyanide (NaCN). These compounds have had a number of industrial uses, from pesticides and the extracting of silver and gold from ore, to dyes and the hardening of metals. They also are deadly poisons.

ecosystem    A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

National Oceanic and Atmospheric Administration, or NOAA      A science agency of the U.S. Department of Commerce. Initially established in 1807 under another name (The Survey of the Coast), this agency focuses on understanding and preserving ocean resources, including fisheries, protecting marine mammals (from seals to whales), studying the seafloor and probing the upper atmosphere.

organism   Any living thing, from elephants and plants to bacteria and other types of single-celled life.

pathologist   Someone who studies disease and how it affects people or other infected organisms.

reef    A ridge of rock, coral or sand. It rises up from the seafloor and may come to just above or just under the water’s surface.

species    A group of organisms that share similar traits and ancestry, and can usually breed to produce fertile offspring. It is also the basic rank in a classification system called taxonomy. A species name (such as sapiens)  is usually given with the next highest rank, the genus (such as Homo).

thiocyanate     It is a highly toxic chemical that can be absorbed through the skin. It is used to enhance the potency of some weed killers and medicines. It is also produced in the body of animals exposed to cyanide. It is a chemical made as the body attempts to detoxify cyanide.

trade      (in economics) A term for industries that make or provide things for sale to others. In this case, they trade products or supplies for money. For instance, the aquarium trade is the industry that provides animals and plants for people who have aquariums.


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R. Umberger and C.A. Downs. Assessing the prevalence of cyanide-caught fish in the U.S. marine aquarium trade. 13th International Coral Reef Symposium. June 24, 2016. Honolulu, Hawaii.

A.L. Rhyne et al. Revealing the appetite of the marine aquarium fish trade: the volume and biodiversity of fish imported into the United States. PLOS ONE. Published online May 21, 2012. doi: 10.1371/journal.pone.0035808.

E.W. Bruckner and G.G. Roberts. Proceedings of the international cyanide detection testing workshop. February 6-8, 2008. U.S. Department of Commerce.

Further Reading

S. Ornes. “Threatened corals get fishy rescue.” Science News for Students. December 6, 2012.

S. Ornes. “Changing climate alters fish behavior.” Science News for Students. June 22, 2011.