Hogchoker

The hogchoker, a right-eyed fish, eats worms and crustaceans. (Clinton & Charles Robertson/CC BY 2.0)

There are more than 700 species of flatfish, several of which are regularly found in the Chesapeake Bay: hogchokers, blackcheek tonguefish, windowpanes and summer, winter and smallmouth flounders. (Bay whiffs and fringed, fourspot, yellowtail and southern flounders are “rare” and “uncommon” visitors to the Lower Bay.) 

A body like a squashed pancake doesn’t lead to automatic membership in the flatfish fraternity. For one thing, flatfish skeletons are made of bone and not cartilage (sorry, rays). And both eyes are located on one side of its upper head (sorry, mola mola). Here are other features that make a flat fish a flatfish.

We flatter ourselves: A flatfish isn’t born flat. Its eyes are located on each side of its head, and it swims in the water column. Within a week or two, the larva moves to the bottom as metamorphosis begins. Its entire skull twists as one eye migrates to the other side until it is close to the other eye. The body turns flat in a couple of weeks. The skin changes colors. The mud-facing side becomes lighter while the water-facing eye side becomes darker. It’s also at this time that the larva switches from pigging out on plankton to become a crustacean-crunching, fish-feasting adult predator. This new diet requires an adaptation in its gastrointestinal system.

Winter flounder

The winter flounder, a right-eyed fish, eats small crustaceans and worms. (National Marine Sanctuaries/Public Domain)

Fintastic finesse: Flatfish have one long dorsal fin and a long anal fin, each stretching from the tail to near their head. This helps them swim sideways. These fins are ray fins — webs of skin held by bony spines — that the fish can bend to create a hollow in the sea floor where they bury themselves. They can also scrunch up their ray fins to push them along the bottom.

Lying low: Flatfish, as a rule, are ambush predators. When they cannot bury themselves, but their nervous system can change their skin color to blend in with their surroundings, from sand and mud to pebbly bottoms. That’s called dynamic camouflage. They spend most of their time waiting for prey to come to them: small invertebrates and crustaceans and other fish. Their camouflage ability also hides them from predators that find flatfish as tasty as most humans do.

Flatfish fossil

The fossil, Amphistium paradoxum, lived 50 million years ago and is an early relative of flatfish. Unlike modern flatfish, which have both eyes on one side of their head, one of the eyes of this “transitional” fossil is located at the top-center of its head. (Totodu74/Wikimedia Commons)

Eye-popping peepers: How does a buried fish know when prey is passing by? Their protruding eyeballs can rotate 180 degrees like periscopes. Flatfish species are either right-eyed or left-eyed, depending on which eye migrates. If the left eye moves right, it is a right-eyed fish. If the right eye joins the left eye, it is a left-eyed fish.

Can you match the listed flatfish to their descriptions? Answers are below.

  • Blackcheek tonguefish
  • Hogchoker
  • Smallmouth flounder
  • Summer flounder
  • Windowpane
  • Winter flounder

1. I’m related to turbots and can grow up to 18 inches long. I have spots on my body and fins, and I’m so thin that parts of me are almost transparent. You can find me year-round in shallow water with sandy and muddy bottoms, most often in the Lower Bay.

2. At 4.5 inches, I’m small enough to be eaten by winter flounder. I have large scales but a small mouth for my body size. I’m olive brown with dark splotches. I’m common in the Lower Bay’s muddy bottoms and channels.

3. A member of the sole family, I’m one of most abundant fish in the Bay. I am 6–8 inches long, a blotchy muddy brown with narrow stripes across my back. I can be found from the Bay’s mouth to tidal freshwater. I’m supposedly quite delicious but my rough scales and abundance of bones make me inedible. This opinion is shared by the livestock that farmers tried to feed me to.

Blackcheek tonguefish

The blackcheek tonguefish, a left-eyed fish, eats small crabs, shrimps, worms and copepods. (Rob Aguilar/Smithsonian Environmental Research Center)

4. I am olive green with reddish brown spots and the thickest fish in this group. In the Bay, I can grow up to 16 inches long but I’m limited to small prey because of my little mouth. I am good eating (even my roe). My young hang around in muddy or vegetated bottoms during the summer while adults head for cooler, deeper water, returning when temperatures get colder. I was once caught near the mouth of the Susquehanna River, but I’m becoming more rare in the Bay. Some say that I might become extirpated here as temperatures rise.

5. Despite being common, I’m rarely seen. My 8-inch elongated body tapers sharply at the tail. I have a black splotch on the cheek and no pectoral (side) fins, and my three other fins are connected and completely surround the body. Instead of hiding in the bottom of a depression, I press my belly against one of its sides.

6. I’m also called a fluke, and I’m an important commercial catch and sportfish. Adults of 30 inches or more are found in the Bay’s deeper open waters in summer. My back has scattered spots.

ANSWERS

  1. Windowpane
  2. Smallmouth flounder
  3. Hogchoker
  4. Winter flounder
  5. Blackcheek tonguefish
  6. Summer flounder

Kathleen Gaskell is the Bay Journal's copy and layout editor and author of the Chesapeake Challenge. Contact Kathleen at kgaskell@bayjournal.com.

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