Our seas are filled with other worldly creatures; some are terrifying, although by fears unfounded, some cause us to laugh, others inspire awe, while still others take us aback when we first encounter them, for they look as if nature played a cruel trick leaving them grossly deformed by human standards.
The order Pleauronectiformes, also known as the Heterosomata, presents us with some of the most bizarre fish, the flatfish. Among the 350 or so species in this order are the flounder, sole, halibut, and turbot.
All of the flatfish begin as translucent larvae, bilaterally symmetrical with pectoral fins on each side and a dorsal fin on top, swimming upright like tuna, snapper, and the goldfish found in pet shops. Depending upon species and environmental factors, somewhere between 25 – 40 days after hatching, the larvae begin the metamorphosis into flatfishes. As the larvae deplete the stores in their egg sacs, their pituitary and thyroid glands begin to develop. While the exact mechanisms remain under study it is believed that the infusion of these hormones triggers the growth of s tomachs, the reconfiguration of boney structures, and the migration and restructuring of eyes which were once flat and located on both the right and left sides of their bodies. And, as the metamorphosis begins the little larvae start leaning to one side.
Upon completion of the six month long metamorphosis the flatfish have transformed from upright swimming fish to side swimming bot tom dwellers. Now-protruding eyes as well as the mouth are found together on one side, while one of the pectoral fins has disappeared. Which side depends mostly upon species; flounders are further differentiated and can be either right-side (Pleuronectidae) or left-side (Bothidae) flounder species, a determination made by the side upon which both eyes are located.
While evolution is a process that takes millions of years, watching the flatfish transform from ‘normal’ looking fish upon hatching to bot tom dwelling adults is like watching evolution fast forward. The flatfish are carnivores, feeding off the bot tom where they must camouflage themselves by both burying in sand and changing colors to match their surroundings. Remaining as upright swimming, symmetrical fish with eyes on both sides of their heads would have precluded their survival long ago.
Though when we first encounter a flatfish we are often taken aback by their seemingly deformed appearance, watching one of the Peacock Flounders found here in the Caribbean is a fascinating experience. With their sand colored upper bodies decorated most commonly by spots of peacock blue, the left-sided Peacock Flounder is one of the most beautiful fish in our waters.
Peacock Flounder have the ability to change colors entirely when the blue rings are replaced by stripes or other patterns of red, browns, or greens so that they match their environments. Scientists have found that one of the Peacock Flounder’s eyes ‘looks’ for environmental colors and patterns—and if that eye is covered the fish looses its ability to blend in. Their stemmed eyes act independently of each other, one looking for environmental changes while the other watches for the next meal.
Peacock Flounder are generally found on sandy bot toms around relatively shallow coral reefs but they have also been found at depths of 280 feet; however, it is difficult to find them because they tend to bury themselves in the sand with only their stemmed eyes protruding as they wait for small fish or crustaceans to pass by. Occasionally they can be found lying in the open upon rocks where their ability to change colors allows them to blend into the rocks’ surfaces. They are diurnal meaning they are active during the day and rest at night, well camouflaged by sand and coloration.
In the winter and early spring, Peacock Flounder can be found swimming in shallow water close to shores where there are currents leading out to sea. A female may lay as many as two or three million eggs per year. Once the eggs are laid, the male fertilizes them before the current carries them many miles out where they float along the surface until the eggs are ready to hatch, about two weeks later. Just before hatching, the eggs sink so the translucent larvae are virtually invisible against the bot tom as they await their 6 month long metamorphosis into flatfish.