American Oceans

Winter Flounder

Winter Flounder – or Pseudopleuronectes americanus – is a coastal fish common to New England. Going by the names flounder, sole, lemon sole, and blackback flounder, this wild fish often appears in aquariums and restaurants.

Winter Flounder or Pseudopleuronectes Americanus on black rock

Currently sitting below its target population in many areas, efforts to rebuild the Winter Flounder population are ongoing.

If you’ve been curious to learn more about the Winter Flounder, we’re here to help. Read on for some interesting, fun facts, as well as information on the Winter Flounder’s habitat, lifespan, and much more.

Characteristics & Appearance

The Winter Flounder has a distinctive appearance that makes it easy to tell apart from most other fish. Here are the physical characteristics of the coastal flatfish.

Weight & Length

Winter Flounder are typically around the same size regardless of sex. They grow above two feet in length and can commonly grow much larger.

They average between four and five pounds, rarely growing significantly larger than this average weight.

Physical Characteristics & Color

Winter Flounder have a thick, oval-shaped body. This shape lets them hide in coastal seagrasses and kelp thickets much easier.

As a flatfish, Winter Flounder are typically much flatter than most fish. Their eyes are on the right side of their body, resting their left on the seafloor. Having both eyes on one side allows them to have better vision, given their shape.

Coloring among Winter Flounder ranges from a muddy brown to a dark red. Shades of olive or deep slate are also common. Their upper side is almost entirely black, though many may have lighter colorations of the shade.

Finally, their underside is almost completely white. The Winter Flounder’s fins have tinges of pinks and reds, with some sporting yellow as well.

They’re much more colorful than most other flounder species capable of camouflage by changing their coloration.

Lifespan & Reproduction

The Winter Flounder has a decently long lifespan among the fish world, living between 15 and 18 years if allowed to live its full lifespan.

Winter Flounder will spawn during the winter and spring, preferring shallow inshore waters. Like many other sea creatures, Winter Flounder tend to return to the areas they were born to spawn.

Females carry between 500,000 to 1,500,000 eggs for a spawning session. They deposit these eggs on the ocean floor about 40 times over the spawning season. When hatched, these flounder are called larvae.

Roughly six weeks after birth, the larvae settle near the ocean floor, where they begin transforming into juveniles.

Over the weeks, their left eye will move to the right side of their body. Survival rates are heavily dependent on water temperature, quality, and salinity.

Once fully adapted into juveniles, Winter Flounder quickly grow into adults. After two years or so, a Winter Flounder is typically considered an adult flounder.


Winter Flounder live in the Atlantic ocean on the east coast of North America. The most common area ranges from North Carolina to the Gulf of St. Lawrence, Canada.

In particular, you can find Winter Flounder just north of Delaware Bay. There are also three main stocks of Winter Flounder in the Gulf of Maine, Georges Bank and the Southern New England/Mid-Atlantic stocks.

Where Do Winter Flounder Live?

Winter Flounder stick close to the shore, especially among seabeds of kelp and seagrass. They can survive in much colder water than other flounder species, including below freezing, with their ideal temperature being between 32 and 50 degrees Fahrenheit.

These fish survive such frigid temperatures with a protein that works as an “antifreeze” agent.

They also tend to lie dormant near the floor of the ocean, where they’ll lie in wait to conserve energy and avoid predators.

Food & Diet

Winter Flounder are predatory hunters that prey on myriad water creatures. Due to better visibility, they primarily hunt during the day and are much more dormant at night. Technically omnivorous, they’ll usually always prefer other fish and crustaceans over plant matter.

What Do Winter Flounder Eat?

At their larvae stage, the Winter Flounder will subsist mainly on plankton. Phytoplankton and zooplankton are both on the menu, eating whatever they can get their hands on as they continue to grow.

plankton for winter flounder to eat

Once they metamorph into juveniles, they eat larger and larger prey, though plankton remains a staple of their diet.

Once adults, Winter Flounder are limited on what they can eat by their small mouths. Larger prey is safe from the Winter Flounder simply because the fish can’t manage to get them into its mouth. 

As adults, they’ll feed mainly on small invertebrates. Shrimps and larger plankton will remain on their menu for as long as they can find them, with shellfish, small crabs, and worms filling out their diet.

small shrimps for winter flounder to eat

Many Winter Flounder will seek out invertebrates like young squids or octopi, depending on the environment. Small mollusks may also find their way into a Winter Flounder’s belly.

Threats & Predators

The Winter Flounder is far from at the top of the food chain. Here are some of the many threats that the Winter Flounder faces throughout its life.

Human Threats

Unarguably, the biggest threat to a Winter Flounder’s safety is humanity. Their coastal habitat makes them exceptionally susceptible to pollution. 

Winter Flounder are also easy to overfish and have rapidly declined in many areas. Most of their habitats along the east coast have laws protecting them or limiting how you can catch them, including requiring specialist gear.

Climate Change & Global Warming

Climate change and global warming play a massive part in the declination of Winter Flounder. These fish prefer colder waters, and the rapidly heating oceans are detrimental to them, especially in spawning and reproduction.

Changing ocean temperatures also affect plankton, the primary food source as larvae and juveniles.


The Winter Flounder has a large number of predators. As adults, they mostly have to worry about the Atlantic cod, the spiny dogfish, and the monkfish.

However, juveniles have many more threats. Many fish will feed on them at this stage, including striped bass, toadfish, and even other flounder. Birds, invertebrates, skates, and many other marine mammals will prey on young flounder.

Other Threats

Their coastal habitat opens them up for threats from much of humanity’s byproducts. Boats going over their habitat can ruin the forests of kelp and seagrass that they call home, making it difficult for them to find safety. Pollution can also kill off them or their food source, spelling disaster.

Trash can also easily end up in their habitat. Oil spills have historically destroyed much of their livable habitats as well.

Conservation Status

The Winter Flounder is subject to overfishing in many of its stocks. Overfishing has depleted the Georges Bank stock, but regulations have helped ease this.

The same is true for the Southern New England/Mid-Atlantic stock. However, the Gulf of Maine stock is not subject to overfishing.

As a whole, the Winter Flounder has a large population, plentiful along much of the North American east coast.

Their numbers are not predicted to fall drastically, and they are currently not endangered or threatened.

Fun Facts About Winter Flounder

  • Winter Flounder are born with an eye on either side of their head, and the left migrates to the right side weeks after hatching
  • Winter Flounder hatch within days of being successfully fertilized
  • Winter Flounder are heavily limited in what they can eat due to their small mouths
  • A unique protein in the Winter Flounder helps keep it from suffering adverse effects of cold waters, letting it survive in below-freezing temperatures
  • The Winter Flounder’s eyes are on its right side, while the summer flounder’s eyes are on its left side
  • A female Winter Flounder can lay eggs more than 40 times in a single spawning season

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