Photograph by Joel Sartore, National Geographic Photo Ark
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Blue tangs can be found in the clear waters of coral reefs. Experts believe that as many as a quarter-million of them are taken from the wild each year for the aquarium trade.

Photograph by Joel Sartore, National Geographic Photo Ark

What is a blue tang?

Blue tangs are small fish native to coral reefs in the Indo-Pacific. The animals are easy to spot, thanks to their characteristically vibrant colorations of royal blue and canary yellow.

The blue tang’s notorious color patterns are not as reliable as you might think. Juvenile blue tangs are bright yellow, for instance. And as adults, the fish will flush deeper blues and violets as a sign of stress.

Blue tangs may look relatively harmless, but when in danger they can raise a pair of razor-sharp, venomous spines on either side of their tails. The fish then whip their bodies from side to side, threatening to stab predators with their toxin-tipped stingers.

Additionally, people who eat blue tangs have been known to develop a serious foodborne illness called ciguatera poisoning. Symptoms include vomiting, diarrhea, and dizziness. Ciguatera poisoning occurs because tangs sometimes eat large quantities of creatures called dinoflagellates, which create several kinds of toxins that build up in the tang’s body.

Mistaken identities

The blue tang goes by many common names, including palette surgeonfish, regal blue tang, hippo tang, flagtail surgeonfish, royal blue tang, Pacific regal blue tang, and blue surgeonfish.

There are also a number of other fish species that are sometimes referred to as blue tangs, including Acanthurus leucosternon, which can be distinguished by its black face, and Acanthurus coeruleus, which lives on the other side of the world in the Atlantic Ocean.

This is why experts assign animals scientific names in Latin. While there are many blue tangs, there is only one Paracanthurus hepatus.

Habitat and diet

Blue tangs can be found in the clear waters on and surrounding coral reefs. They inhabit a wide range across the Pacific and Indian Oceans that stretches from American Samoa to the eastern coast of Africa.

While blue tangs are omnivores and have been known to chow down on tiny aquatic creatures known as plankton, the bulk of their diet comes from algae. The fish use small, sharp teeth to nip and scrape algae off the coral reef.

This makes the fish important cogs within the larger ecosystem. Without blue tangs and other fish that perform this algae-cleaning service, the plants would suffocate and kill coral, sending the whole food chain into disarray.

Threats to survival

While the blue tang is listed as a species of least concern by the International Union for Conservation of Nature (IUCN), there is some worry about the way the fish is targeted by the aquarium trade. Until 2016, no one knew how to breed blue tangs in captivity, which means that all of the fish being sold into the market were sourced from the wild. Experts say this could mean as many as a quarter-million blue tangs have been removed from their homes on reefs each year.

Worse still, blue tangs and other wild reef fish are commonly caught with squirt bottles full of cyanide, which stun the fish long enough for people to catch them. Juveniles are usually targeted because they flock to stony corals where they can be caught en masse. But that method can also kill the fish on contact, as well as injure or kill other animals nearby.

The coral reefs that the blue tang call home are also under threat from things like ocean acidification and coral bleaching. This means habitat loss may also be a danger to the fish.

Conservation

National Geographic grantee Shannon Switzer Swanson has been documenting the trade in wild-caught saltwater fish, including blue tangs, for aquariums and doing research to better understand fishing communities in Indonesia that participate in the trade.

The discovery of how to breed blue tangs in captivity may one day mean that it’s not necessary to capture the animals in the wild. However, it will take time before those findings can be scaled up to meet the high demand for this species among aquarists.


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