Over the past several months, a photograph of a so-called "micro tang" has gone viral on more than one occasion, and the creature's strange appearance has sparked all sorts of questions from online commenters. Is the fish a fake? How big will this "micro" fish get? Is it dead? Is it a mutant?

Ask and the answers you shall receive. 

Image: Kevin Mattson

First off, this isn't a "micro" anything – but it is a real fish. What you're looking at is a larval (baby) surgeonfish in the genus Acanthurus. In a matter of months, tiny wonders like this one grow up to be a respectable ten to 12 inches (about 30cm) long. 

It seems this case of miniature mistaken identity can be traced to the Mr Good Travel Instagram page, who identified the fish as a "micro tang" in a post that racked up over 58,000 likes earlier this year. Before long, the fishy ID had surfaced on RedditFacebook and countless Pinterest boards.

The original image, however, belongs to Kevin Mattson, who notes that he released the fish alive, and in seemingly good condition, after the photo was taken. 

Mattson identified the fish as a blue tang. That name probably sounds familiar – thousands of parents flooded pet shops to buy one after Disney's "Finding Dory" hit the big screen. (Don't buy Dory – here's why.)

But the Dory ID isn't quite right either.

The common name "blue tang" is used for two different species of surgeonfish. Dory is a Pacific blue tang (Paracanthurus hepatus), and while that species does have a translucent larval stage, black banding near the tail and slightly different internal colouration make it a little different from Mattson's catch.

The second species is the Atlantic blue tang (Acanthurus coeruleus). This is definitely a warmer guess, and several media outlets settled on it as the correct ID. But Mattson scooped his specimen in Puerto Vallarta, which sits along Mexico's Pacific coast. That location falls well outside the native range for A. coeruleus. 

So what did Mattson really find? Our money is on a baby Achilles tang (Acanthurus achilles) or whitecheek surgeonfish (Acanthurus nigricans), both of which are commonly spotted off the coast of Baja. But that's just a hunch. 

Either way, we can definitely rule out "mutant invisible fish". Many fish species have translucent larva, and the see-through strategy makes sense: when you're tiny and defenceless, staying out of sight is key to survival. Baby Dorys, for example, don't turn blue for about 55 days.

If you have more information on this crazy critter, let us know in the comments below! 



Top header image: Elyne Dugény/Flickr