SCIENCE

While you’re sitting around waiting for the movie start, here are 5½ facts you can drop about Dory’s species, the blue tang. (Mental Floss)

How do scientists study blue tangs? With coral reef surveys like this one.

Educators, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Discussion Ideas

• 1. Blue tangs aren’t always blue, and they’re not always tangs.
  • Juvenile blue tangs are bright yellow. And adult blue tangs can actually modulate their color based on environmental conditions. Under stress, for example, their blue coloration deepens to violet and the black marks may become slightly bleached.
    • Blue tangs get their color from cells called iridiphores, a type of chromatophore. Iridiphores are crystal structures of guanine (the famous G in our DNA tetrarchy of guanine, cytosine, adenine, and thymine). The crystalline arrangement reflects light at a specific spectrum and determines the animal’s color.
  • Dory’s species of blue tang, Paracanthurus hepatus, has many different names: blue tang, doctorfish, common surgeon, regal tang, palette surgeonfish, royal blue tang, hippo tang, flagtail surgeonfish, Pacific regal blue tang, and blue surgeonfish.
    • Paracanthurus hepatus is often confused with Acanthurus leucosternon and Acanthurus coeruleus. The three fish look very different, but are all known as blue tang—be careful when you’re researching!

• 2. Blue tang are everywhere and nowhere.
  • Blue tang are not listed on the IUCN list of endangered species; their populations are pretty healthy and they’re of “least concern.” However, as a nice sentence on Wikipedia notes, “the species’ range is broad, but it is common nowhere.”
    • Blue tang are indigenous to warm, shallow tropical reefs of the Indian and Pacific Oceans.
  • Blue tang are entirely helpless when they hatch, lacking a pigments, eyes, a mouth or even a heartbeat. They drift with the currents for about five hours after hatching.

• 3. Blue tang are important parts of the coral reef food web.
  • Adult blue tangs are omnivores that feed primarily on algae, but can also consume plankton. These first-order consumers keep “algae levels on coral down to a manageable level. Without the blue tang there to eat their fill, algae could overgrow and suffocate the reefs.”
  • Blue tangs themselves are prey for important secondary consumers such as tuna, grouper, and barracuda.

• 4. Blue tangs are poison.
  • Blue tangs often carry a toxin called ciguatera. Symptoms of ciguatera poisoning are usually limited to vomiting and diarrhea, but may also include more serious symptoms such as headaches, muscle aches, and even hallucinations and heart and breathing problems.
    • FYI: Some scientists think an outbreak of ciguatera poisoning in islands of the Malay Archipelago may have prompted the great Polynesian ocean migrations of the early 1000s. (!!!)

• 5. Blue tangs will cut you.
  • As its “surgeonfish” name indicates, blue tangs are handy with scalpels. The fish have caudal spines—very sharp spines that can be extended from either side of their caudal peduncle (the area where the tail joins the body). The caudal spine contains toxins that can cause a debilitating pain to small predators and uncomfortable irritation and pain in humans. Blue tangs extend their caudal spine and thrash around when threatened.
    • The defense mechanism is useful. Some parrotfish, which are similarly colored but lack caudal spines or toxins, often join groups of blue tang for protection.

• 5½. Think twice before adding a blue tang to your aquarium.
  • Blue tangs are already some of the most popular fish in saltwater aquariums, and many scientists and businesses think Finding Dory will only increase demand. However, while the aquarium trade may help save many species of reef fish (including clownfish—Nemo!), it doesn’t bode as well for the blue tang. The reason:
    • Blue tangs are not bred in captivity. That means they’re all caught in the wild, putting a stress on natural populations.

TEACHERS TOOLKIT

Mental Floss: Understanding ‘Dory’: 5 Facts About the Pacific Blue Tang

Nat Geo: Coral Reef Fish Survey Simulation activity

Nat Geo: Coral Reef Food Web illustrations

Animal Diversity Web: Paracanthurus hepatus