What is a Flatfish?

Mary McMahon
Mary McMahon

A flatfish is a fish in the order Pleuronectiformes. The fish are extremely unusual, and in addition to being valuable food fish, flatfish are also the subject of intense scientific scrutiny. Certainly an encounter with a flatfish is never forgotten, as the fish look truly bizarre. Many species also happen to be quite tasty, making flatfish a common inclusion on restaurant menus and in the cases of fishmongers.

Flatfish are a popular catch for the fishing industry.
Flatfish are a popular catch for the fishing industry.

Flatfish start out living perfectly ordinary lives. When they initially hatch, they are bilaterally symmetrical, as are many other animals on Earth. However, as they mature, flatfish slowly become laterally compressed, and their bodies undergo changes which cause them to start swimming on their sides. Since flatfish live on the bottom of the ocean, this adaptation would render one of their eyes essentially useless. Fortunately, nature comes to the rescue, because flatfish have migrating eyes. As they mature, one eye slowly migrates to the top side of the fish, so that the fish end up with both eyes on one side of their body.

As a general rule, the blind side of a flatfish is pale, while the top side is dark or mottled. These color adaptations assist with camouflage. When the fish reach full maturity, they are far from symmetrical, since they live their lives on their sides. Many of the flatfish also look extremely peculiar, since they are so compressed. Indeed, they have been unfavorably likened to roadkill, since their bodies have a slightly squashed appearance.

The coloration of flatfish allows them to conceal themselves along the sandy or rocky floor of bodies of water. Unsuspecting dish drifting by overhead become easy prey. The fish can move rather quickly, considering their strange body morphology. Fishermen can catch flatfish either with hooks and lines or through dredging with nets. Dredging is not very environmentally friendly, however, as it profoundly disturbs the marine environment.

There are approximately 500 species of fish which are considered flatfish. Of these, flounder, sole, halibut, turbot, dabs, and plaice are among the most popular for food fishes. Many flatfish are also sustainably harvested or farmed, making them excellent ecological choice, for people who are concerned about the fishing industry. The fish tend to have white flesh, which can be firm to very tender and flaky. Given the wide range of species, there are a number of ways to prepare and season flatfish, ranging from broiling to grilling, with sauces like lemon dill sauce to mango salsa.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@browncoat - Another fun fish to spot when you are snorkeling or scuba diving is the moray eel. I always check out all the crevices in the rocks to see if I can see one.

But I have to say I would rather spot a flatfish on my plate! My uncle used to catch flounder and let us have some and I think they are really delicious.

I don't live close enough to him to take advantage of his flatfish lures anymore but I still try to get them at the fish market when they are fresh.

You can tell by checking the smell. If they smell too "fishy" they are no longer fresh.


Flat fish might be ugly, but they are incredibly fun to spot when you are out snorkeling. I'd always wanted to see one and the first time I did it made me really happy. I know, dorky right? They are just so difficult to find, as they are the color of the sea floor and they kind of swish themselves into the sand as even better camouflage.

I tried pointing it out to my friend and she couldn't see it, even when I swam down and tried to show her. It wasn't until the fish moved that she spotted it!


This is a really amazing fish species. I think it's also a great example of evolution and how species adapt physically to changing circumstances.

If one of the eyes of flatfish didn't migrate to the other side when they are older, that eye would always be staring at the sand because of the way they lie down on the ocean floor.

But they have adapted to those conditions by having both eyes on one side. It is so logical and natural! I think it shows the potential of all species to transform and survive.

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