Flounder are a diverse group of flatfish, characterized by their flattened bodies and their preference for dwelling on the ocean floor. These demersal fish are found in various aquatic environments worldwide, including oceans and estuaries. Their body shape allows them to lie inconspicuously on the seabed, a characteristic central to their survival and feeding strategies. They are an example of adaptation to a bottom-dwelling lifestyle.
Common Prey
Adult flounder are carnivorous, primarily consuming bottom-dwelling or slow-moving organisms. Their diet includes small fish like mullet, anchovies, and menhaden, ambushed from their camouflaged positions on the seafloor. Crustaceans, such as shrimp and crabs (e.g., mysid shrimp, sand shrimp, and various amphipods), form a significant portion of their diet.
Mollusks, including bivalves like clams and occasional cephalopods such as squid, also contribute. Worms, particularly polychaetes, are another food source. Diet composition varies by location and prey availability, allowing flounder to capitalize on the most abundant food sources.
Feeding Habits and Adaptations
Flounder employ specialized adaptations for their bottom-dwelling feeding habits. A primary adaptation is their camouflage ability; specialized skin cells allow them to rapidly change color and pattern to blend seamlessly with the seafloor. They can also partially bury themselves in sediment, leaving only their eyes exposed, which is essential for ambush predation.
When prey comes within striking distance, flounder lunge forward swiftly. Their unique eye migration is another adaptation; born with one eye on each side, one eye migrates as they mature, positioning both on the upward-facing side of their flattened body. This provides a wide field of vision for spotting prey while lying flat. Flounder primarily use suction feeding, rapidly expanding their mouth cavity to create a vacuum that draws in organisms.
Diet Across Life Stages and Species
The diet of flounder varies considerably across life stages and species. Juvenile flounder typically consume smaller organisms, with larval and post-larval stages often feeding on zooplankton and small crustaceans such as copepods and mysid shrimp. As they grow, their diet shifts, transitioning from microscopic meiofauna to larger macrofauna, including small invertebrates such as amphipods, isopods, and bivalve siphons.
Adult flounder incorporate more substantial prey into their diet, frequently including larger crustaceans and a variety of fish species. For instance, Summer Flounder, also known as fluke, are opportunistic feeders, consuming a mixed diet of fish and invertebrates, with larger individuals preying on fish like weakfish, spotted hake, and even juvenile Winter Flounder. Dietary variations between species, such as the Arrowtooth Flounder, can also be influenced by geographical location and water depth, reflecting regional prey availability.