Flounder are indeed fish, unequivocally classified within the vast and diverse group of aquatic vertebrates. Their distinctive appearance, particularly their flattened bodies and unusual eye placement, often leads to questions about their classification. While they may not resemble a typical fish swimming upright with eyes on either side of its head, their unique form is a result of remarkable adaptations that allow them to thrive in their specific marine environments.
Understanding Flounder as a Fish
Flounder belong to the animal kingdom, specifically within the phylum Chordata, which includes all vertebrates with a backbone. They are further classified under the class Actinopterygii, or ray-finned fish. Within this class, flounder are part of the order Pleuronectiformes, a group of flatfish encompassing over 500 species including soles and halibuts.
Despite their unique morphology, flounder possess characteristics shared by all fish. They breathe using gills, which extract oxygen from water. Their bodies are supported by a vertebral column, or backbone, which is a defining feature of vertebrates. Flounder also have fins for movement and stability, although their dorsal and anal fins are notably elongated, spanning much of their body length to facilitate their distinctive undulating movement across the seafloor. Most flounder species are covered in scales, and they are cold-blooded.
Flounder’s Unique Characteristics
The most striking feature of flounder is their flattened body shape, which is a specific adaptation for life on the seabed. They lie almost perfectly flush with the ocean floor, minimizing their profile and allowing them to blend seamlessly with the substrate. This flat form is not present at birth; flounder larvae begin life resembling typical fish, swimming upright with an eye on each side of their head.
Metamorphosis occurs after hatching. During this process, one eye gradually migrates across the top of the head to join the other eye on a single side. This eye migration involves complex changes. Once complete, both eyes are positioned on the upper surface, allowing the flounder to observe its surroundings while lying flat on the bottom. The eyeless side typically loses its color and becomes the underside.
This unique body structure is complemented by remarkable camouflage abilities. Flounder can rapidly change the color and pattern of their eyed side to match the surrounding sand, gravel, or mud. This is achieved through specialized skin cells called chromatophores, which can expand or contract to alter the fish’s appearance. This camouflage is important for their survival, enabling them to hide from predators and ambush unsuspecting prey like small fish, shrimp, and crabs.