Pleuronectiformes
Pleuronectiformes, commonly known as flatfishes or flounders, is an order of fish characterized by their laterally compressed bodies and the remarkable ability to lie on their sides. This adaptation, known as asymmetry, allows them to camouflage themselves effectively on the seabed, often blending seamlessly with the sand, gravel, or algae. Flatfishes are found in both marine and brackish waters worldwide, inhabiting a variety of depths, from shallow coastal areas to the abyssal depths of the ocean.
Characteristics
Pleuronectiformes exhibit several distinctive features that set them apart from other fish orders. Their most striking characteristic is their flattened body shape, which results from a developmental process called lateralization. During larval stages, they possess a typical, symmetrical body plan, but as they grow, one eye migrates to the opposite side of the head, resulting in both eyes being on the same side of the body. This process gives them their characteristic flat appearance. Other distinguishing characteristics include:
- Asymmetry: One side of the body, called the blind side, is usually pigmented, while the other side, the eyed side, is pigmented and contains both eyes.
- Mouth: The mouth is usually skewed, with the jaw on the eyed side typically larger than the jaw on the blind side.
- Fins: They possess a dorsal fin that runs along the entire length of their upper body, a pectoral fin on each side, a caudal fin (tail fin), and an anal fin on the underside of their body.
- Scales: Most species have small, cycloid scales (smooth, rounded scales).
Environment and Distribution
Flatfishes inhabit a wide range of marine environments, including coastal waters, estuaries, and the open ocean. Some species prefer sandy bottoms, while others favor rocky reefs, coral reefs, or muddy seabeds. Their distribution is global, with species found in all oceans except the Arctic Ocean. Some flatfishes are demersal, meaning they live close to the bottom, while others are pelagic, living in the water column.
Diet and Behavior
Flatfishes are carnivores, feeding primarily on invertebrates such as crustaceans, mollusks, and worms. Some larger species also prey on small fish. They typically lie in wait on the seabed, using their camouflage to ambush prey. Their flattened body shape allows them to remain perfectly still for long periods, blending seamlessly with the surroundings.
Commercial Importance
Many flatfish species are commercially important and are widely caught for consumption. Some of the most popular flatfish species include halibut, sole, flounder, and turbot. These species are often prized for their delicate flavor and firm texture.
Classification
The order Pleuronectiformes is divided into two suborders: Psettodoidei and Pleuronectoidei. The Psettodoidei contains only one family, the Psettodidae, which includes the single genus Psettodes. The Pleuronectoidei comprises nine families, including:
- Bothidae (Lefteye Flounders)
- Citharidae (Citharids)
- Cynoglossidae (Tonguefishes)
- Paralichthyidae (Lefteye Flounders)
- Pleuronectidae (Right-eye Flounders)
- Poecilopsettidae (Poecilopsettid Flounders)
- Scophthalmidae (Turbots)
- Soleidae (Soles)
- Symphysanodontidae (Symphysanodontid Flounders)
References
For further information, please refer to the following resources: