Flounder is the common name for a group of flatfish belonging to the order Pleuronectiformes. These fish are best known for their flattened bodies and the unique placement of both eyes on one side of the head. As bottom-dwelling fish, flounders spend most of their lives resting on the seafloor. Their mild, delicate white flesh has made them an important food fish in Korea and many other countries, where they are enjoyed as sashimi, grilled, braised, steamed, or fried dishes.

In this article, we’ll explore the flounder’s characteristics, habitat, behavior, diet, reproduction, and ecological importance.

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What Is a Flounder?

Flounders belong to the order Pleuronectiformes, which includes numerous species of flatfish.

Common species found in Korean waters include the Marbled Flounder, Brown Sole, Stone Flounder, and several other flatfish species.

Flounders are widely distributed throughout the East Sea (Sea of Japan), Yellow Sea, and South Sea around Korea, as well as the North Pacific, North Atlantic, European coastal waters, and the coasts of North America.

Adult flounders generally measure:

• Body Length: Approximately 20–50 cm (8–20 inches)
• Maximum Length: Up to 100 cm (39 inches), depending on the species
• Weight: Approximately 300 g–5 kg (0.7–11 lb)

Their average lifespan is about 10–20 years, depending on the species.

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Characteristics of the Flounder

1. Both Eyes on One Side of the Head

The flounder’s most distinctive characteristic is that both eyes are located on the same side of its head.

As larvae, flounders look like ordinary fish with one eye on each side. During development, however, one eye gradually migrates to the opposite side, resulting in the unique appearance of the adult.

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2. Flattened Body

Flounders have an extremely flat, laterally compressed body.

This body shape allows them to lie close to the seafloor, helping them avoid predators and ambush unsuspecting prey.

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3. Exceptional Camouflage

Flounders possess remarkable camouflage abilities.

They can change their body coloration to closely match the surrounding sand, gravel, or seabed, making them extremely difficult for both predators and prey to detect.

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Behavior

Flounders are bottom-dwelling carnivorous fish.

Their typical behaviors include:

• Living on the seafloor
• Resting while partially buried in sand
• Hunting by ambush
• Leading a mostly solitary lifestyle
• Being active during both day and night
• Migrating during the spawning season

They are often observed lying almost completely buried beneath the sand, with only their eyes exposed to watch for approaching prey.

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Diet and Habitat

Flounders are carnivorous fish.

Their primary food sources include:

• Shrimp
• Crabs
• Marine worms
• Small clams
• Small fish
• Various bottom-dwelling invertebrates

Preferred habitats include:

• Sandy seabeds
• Muddy bottoms
• Coastal waters
• Continental shelf regions
• Marine depths of approximately 10–300 meters (33–984 feet)

Different species inhabit environments ranging from shallow coastal waters to much deeper offshore habitats.

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Ecological Importance

Flounders are important mid-level predators in marine ecosystems.

By feeding on benthic invertebrates and small fish, they help regulate prey populations and maintain ecological balance.

They also serve as prey for large fish, sharks, seals, and seabirds, making them an essential link in the marine food web and contributing to the health of seafloor ecosystems.

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Relationship with Humans

Flounders are among the most economically valuable food fish in Korea and many other countries.

They are widely prepared as sashimi, grilled fish, braised dishes, steamed fish, fried fillets, and dried seafood, prized for their mild flavor and tender white flesh.

Flounders are also rich in high-quality protein, omega-3 fatty acids, vitamin B12, and selenium, making them a highly nutritious seafood.

To ensure sustainable populations, many countries have implemented catch quotas, seasonal fishing closures, juvenile release programs, and fisheries management regulations.

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The flounder is a remarkable bottom-dwelling fish distinguished by its unique eye placement, flattened body, and extraordinary camouflage abilities. As an efficient ambush predator, it plays a vital role in maintaining the balance of marine ecosystems while also serving as one of the world’s most popular and nutritious seafood species.

With continued conservation of healthy marine habitats and responsible fisheries management, flounders will remain both an ecologically important species and a valuable seafood resource for generations to come.