Getting to know the Peacock flounder.

By Kelly Currington

I’m pretty confident in saying that most of us have seen “The Little Mermaid” movie and probably fell in love with Ariel’s adorable little sidekick, Flounder. Though not actually a flounder fish, he wiggled his way right into people’s hearts and became a household name, so much so, that people often associate the word “flounder” with this animated character.

Though not as plump or as traditionally “cute” as Ariel’s flounder, the Peacock founder (Bothus Iunatus: Genius Bothidae) is a beautiful and unique creature with just as big a personality—you just have to take the time to get to know them.

This pair of male and female flounders are likely initiating a mating dance.

Whether snorkeling or diving in the stunning waters of the Turks & Caicos Islands, you have undoubtedly passed right over this obscure fish and never knew it, as they are masters of disguise. You think you see movement in the sand out of the corner of your eye, but when you turn to look, you see nothing more than sand—but there is something there, invisible in plain sight.

Flounder are distinctly identifiable by their flatness and shape of their bodies—lending to their other known name of flatfish—and having both eyes on one side of their bodies. Amazingly, these pronounced physical characteristics are not present at birth, but instead develop over the course of three growth stages: egg, larval, and adulthood.

They start life with one eye on each side of their head just like most fish, but then something straight out of a science-fiction movie happens as they mature from larvae to adulthood, through a process called metamorphosis. One eye literally migrates to the other side of the fish’s head through a slit formed during separation of the dorsal fin from the cranium, resulting in both eyes being positioned on the same side, which renders the fish blind on the side the eye moved from. This method is distinctive of this species. Peacock flounders’ eyes are on the left side, which is more brightly colored than the right.

This close-up shows how a flounder’s eyes are both on the right side of the body, giving them better vision as they lay buried in sand.

This eye migration is a crucial adaptation of nature that is necessary for their survival. Flounder lay buried in the sand, hiding from predators and hunting potential prey, so if their eyes were on opposite sides of their head they would have a limited range of vision, leaving them vulnerable to predators and it would diminish their ability to hunt effectively. 

Their coloration is also different from larvae to adulthood, as the pigment cells (larval melanophores) which are located on both sides of the body in low abundance, disappear from the blind side and are only present on the side with the eyes. Other changes are also happening at this time—their body depth increases, they become more rounded in shape, the swim bladder disappears, and teeth develop. 

Another interesting tidbit about these flat fish is that the pelvic fin on the eye side is longer than the side with no eye. Luckily, this asymmetry does not hamper the flounder’s mating game. In fact, a male will breed with up to eight spotted beauties in his territory year-round.

The warming and cooling of the sea is what most likely controls when spawning happens. The male and female flounders approach each other and touch snouts, then the female will swim away. If the male follows, the mating dance begins. He approaches her from the left side and raises his pectoral fin high. She moves her pectoral fin up and down, possibly signaling that she’s ready to mate. The male will slide underneath her and they slowly rise together off the sea floor to a height of around two meters (approximately six and half feet), where the male releases his sperm at the same time the female releases her large clutch of eggs, creating a cloud of sperm and eggs in the water column. This process ensures that the highest number of eggs will be fertilized in what is called “serial spawning.”

This process only lasts only about 15 seconds and then both fish return to the sea floor where the male will “check” the female to ensure her eggs were released. If he detects that they were not, he will repeat the dance until he is satisfied the spawning was successful. Once he is satisfied, the male and female will return to the floor and swim away from each other quickly.

The spawning is intentionally done in the water column so that the eggs will be carried by the currents. Fertilized eggs float near the surface as they drift, but as the embryos develop, the eggs sink. Around fifteen days after the mating dance, the hatchlings emerge and float in the open ocean for the next four to six months, going where the current takes them. This is when the magical eye migration happens.

This male Peacock flounder is raising his pectoral fin, one of the first steps in the mating dance.

Don’t underestimate this serial lover, the male is also a formidable adversary and protects his territory and his ladies with an unexpected fierceness, running off any other male attempting to play on his turf or woo one of his paramours. These females are vital to the longevity of the species as they can lay two to three million eggs each year, increasing the odds of survival. 

Since camouflage directly contributes to a flounder’s survival, nature has equipped them with the ability to blend into their background in less than eight seconds by changing color to match their immediate environment like sand and coral. This enables them to flee from predators and hide in plain sight. In one study they were even capable of matching a checkerboard pattern. (Can you imagine how much fun “hide & seek” would have been as kids if we could do this?) There is still a lot that isn’t understood about how they control the change, but studies have found that it is directly linked to their vision and hormones and is controlled through neurotransmitters, which send signals that mediate changes in the melanophores. Different colors result from different concentrations of pigment granules in different areas. 

Though flounder do rely heavily on ambushing their prey, they are also active hunters and can swim steadily at about 0.37 miles per hour, hitting bursts of nearly 0.5 miles per hour. That’s pretty quick for a little flat fish. Flounder prey mainly on benthic organisms (creatures that live on the sea floor) such as small crustaceans like shrimp and crabs; fish including anchovies, mullet, and menhaden; and invertebrates.

Flounder are mainly solitary creatures, coming together to spawn. Individual male and female territories differ in size, with males having a larger territory and females having more sub-territories within the male’s boundaries. Males have a home turf ranging from 50 to 360 m², and one male’s territory does not overlap another’s. The females’ turf ranges from 20 to 50 m². Both genders spend their days and nights in different areas. Male flounder spend their nights closer to shore, while females seek deeper water; both return to their daytime territories early in the morning. 

Larger fish like snappers, sharks, and rays are predators of flounder. When a perceived threat presents itself, flounder dive into the sand and bury themselves in the substrate, leaving only their eyes exposed, or change their color to perfectly match coral they may be on. Since each eye can move independently of the other, they have a clear view of the world above them and will only reappear when the threat has been eliminated. They can sense movement and vibrations in the water through their lateral line. This allows them to “feel” the water and know if it’s safe to emerge.

It’s estimated that these fish can live up to ten years. They can be found in very shallow waters, literally skimming the shoreline, to as deep as 80 meters (262 feet), so whether snorkeling off the beach or diving on the reef, you are likely to enter flounder territory. This is one reason to be aware and careful where you walk in the shallows and where your fins are when diving. 

Flounder move through the water with grace and elegance, their bodies flowing over the floor with absolute precision. The first time I encountered a swimming flounder, it reminded me of a little magic carpet and that’s still how I describe them.

When you are lucky enough to be immersed in the sea, regardless of the depth, slow down and soak it all in. Sharpen your awareness of the creatures that call it home and you will open a world seen through the eyes of Ariel. Protect and preserve this wonderland!

Author Kelly Currington says, “I always turn to the sea when my soul needs calming. Being immersed in the weightlessness of the underwater world and absorbing all the energy that it holds is a healing process for me. Learning as much as I can about the creatures I encounter connects me to the sea and brings a level of respect and an appreciation for them that drives me to be a better version of myself. I hope sharing what I learn will do the same for others.”