“Flounder” is the common name for a diverse group of flatfish species. They belong to the suborder Pleuronectoidei, but no scientific name exists for the flounder. Instead, the term describes numerous species across several families, including Achiropsettidae (Southern Flounders), Pleuronectidae (Right-eye Flounders), Paralichthyidae (Large-tooth Flounders), and Bothidae (Left-eye Flounders).
These flatfish are masters of camouflage and live on the bottom of oceans worldwide. Among these families, the Paralichthyidae, or large-tooth flounders, are one of the most widespread. Continue reading to explore more about them.
Appearance
The most remarkable feature of a flounder is its asymmetrical body. As a flounder matures from its larval stage, one eye migrates to the other side of its head, resulting in both eyes being on the same side.
The size of a flounder varies significantly by species, with a typical length ranging from 9 to 24 inches. However, some species can grow as long as 37 inches. Their flattened bodies are an adaptation for their life on the seafloor. With two large, round eyes often raised on short stalks, they can have a wide field of vision above them while remaining buried in the sediment. These eyes can also move independently of one another.
The upward-facing side of the flounder is pigmented, often in patterns that provide excellent camouflage against the sand, mud, or gravel below. The blind side, which rests on the seafloor, is typically white or very pale.
The flounder’s incredible transformation from a normal-looking larva to a flatfish is triggered by the hormone thyroxine, the same hormone that causes a tadpole to change into a frog.
Common species
- Pleuronectidae (Right-eye Flounders): This family contains flounders whose eyes are typically on the right side of their head and includes many important food fish like plaice and halibut.
- Bothidae (Left-eye Flounders): This family is characterized by having both eyes on the left side of the body, and its members are often found in tropical and temperate seas.
- Paralichthyidae (Large-tooth Flounders): These are left-eyed flounders known for their large mouths and sharp teeth, which are adaptations for their predatory lifestyle.
- Achiropsettidae (Southern Flounders): This is a small family of flounders living only in the Southern Hemisphere, and they are unique because they lack pectoral fins on their sides. The southern flounder, Paralichthys lethostigma, is the largest of more than 25 species of flatfish found in Texas coastal waters. It is highly prized as both food and a recreationally harvested fish, and accounts for more than 95 percent of the flounder harvest in the state. Their tolerance to low salinity (less salty water) dramatically increases with age.
Habitat
Flounders inhabit the bottom of seas and oceans, often found near piers, bridges, and reefs. They are distributed in coastal estuaries and continental shelves worldwide, from temperate to tropical waters. The highest diversity of species is found in the Indo-West Pacific.
Southern flounder occur from North Carolina to the mouth of the Rio Grande and southward into Mexico.
Most flounder live at depths from the shoreline down to 1,600 feet, though some have been found at depths of over 5,000 feet. The conservation status of many flounder species is not fully known, but several commercially important species have been subject to overfishing and are now under strict management plans to ensure sustainable populations.
Diet
Flounders are skilled ambush predators, often hunting at night. They lie in wait, camouflaged on the ocean floor, before striking at unsuspecting prey. Their diet primarily consists of small fish, crustaceans, shrimp, and worms.
The specific composition of their diet varies by species and location.
Reproduction
Flounders begin life as symmetrical larvae that swim upright in the water column like typical fish. During this planktonic stage, they undergo a remarkable metamorphosis. When larvae develop into juveniles, their right eye moves across the top of the head to the left side. Summer flounder grow fast and have a relatively short life, about 12 to 14 years.
Males grow to more than 2 feet long, and females grow up to 3 feet. They can reproduce when they reach age 2 or 3. Summer flounder spawn in the fall and early winter when they migrate offshore.
Spawning occurs from October through February off the southeast Atlantic and Gulf coasts as water temperatures drop from about 73 degrees to 57 degrees Fahrenheit.
After this transformation, the young flounder settles on the seafloor, lying on its blind side, to begin its life as a bottom-dweller. The flounder’s incredible transformation from a normal-looking larva to a flatfish is triggered by the hormone thyroxine, the same hormone that causes a tadpole to change into a frog.
Threats
Due to their effective camouflage, adult flounder have few natural predators, but they can be prey for sharks, eels, and larger fish. Most of the species have been categorised as Least Concern by the IUCN. Their primary defense is to blend in with the seabed, making them nearly invisible.
The most significant threat to flounder populations globally is commercial and recreational fishing. Their mild, delicate flesh is highly valued, making them a popular target. This has led to overfishing in many regions, and fisheries are now often regulated to protect stocks from collapse.
7 More Interesting Facts About Flounders
- A flounder uses its fins to quickly burrow into the sand, leaving only its eyes visible.
- The lifespan of a flounder varies by species, typically ranging from 3 to 10 years in the wild.
- While they are capable of quick bursts of speed to catch prey or evade predators, they are not long-distance swimmers.
- Gulf flounder have numerous white spots scattered over the body and fins.
- The weight of a flounder is highly variable. While some large specimens can reach 15-20 pounds, many common species are much smaller.
- Fossil records show that flatfish have been around for at least 50 million years, with early ancestors showing intermediate stages of eye migration.
- While most flounder families are either “right-eyed” or “left-eyed,” the starry flounder is unique because individuals from this species can be either.
FAQs
Are Flounders dangerous?
A Flounder is not harmful to people, but it can be harmful to worms or other small aquatic animals. In coastal areas with a healthy population, they can be discovered deep underwater or on murky surfaces. Although they can locate prey in both of these locations, humans are a threat to their survival owing to overfishing.
How long does a Flounder live?
The usual lifespan of a Flounder is 3-10 years. Numerous things affect how they will live. These aquatic species’ lives are in danger, particularly because of global warming. The demise of many species that dwell in water is caused by a variety of factors, including water pollution. When rubbish is dumped into water bodies, Flounder eat it and frequently perish as a result.
Can a Flounder bite you?
Although flounders are carnivores, meaning they consume meat, their bites are unique from those of other carnivores. Typically, a flounder bite does not have to be painful; in other cases, it may not even feel like a bite at all.
