Flounder are bottom-dwelling creatures adapted to their environment, and their diet reflects this specialized lifestyle. These flat-bodied fish are predatory carnivores, primarily consuming other animals found on or near the seabed. Their feeding habits are tied to their physical adaptations and the diverse aquatic habitats they occupy.
Main Dietary Components
Flounder primarily feed on a variety of invertebrates and smaller fish. Their diet includes crustaceans such as shrimp, crabs, and krill, along with marine worms like polychaetes. They also consume mollusks, including small clams and squid, and sometimes sea urchins.
Beyond invertebrates, flounder are active predators of small fish, such as mullet, anchovies, menhaden, and sand eels. They also prey on juvenile herring, Atlantic silverside, and other small bottom-dwelling fish. Fish eggs are another part of their diet.
How Flounder Diets Change
A flounder’s diet changes throughout its life stages, adapting to its size and developmental needs. Larval flounder feed on microscopic organisms like zooplankton and tiny crustaceans. As they grow into juveniles, their diet shifts to include small benthic invertebrates such as mysid shrimp, sand shrimp, amphipods, and chironomid larvae, along with small fish.
Adult flounder consume larger invertebrates and a broader range of small fish, reflecting their increased size. Environmental factors also influence their food choices. In estuaries, flounder larvae rely heavily on the benthic food web, while adults in muddy habitats consume more invertebrates. Conversely, flounder in sandy areas feed more on fish, and those in seagrass beds show a balanced intake of both fish and invertebrates. Seasonal changes also play a role, with prey availability dictating shifts in their feeding patterns.
Flounder Feeding Behavior
Flounder use their body structure and camouflage to capture prey. Their flattened bodies allow them to lie flush with the ocean floor, blending seamlessly with sand, mud, or gravel. They possess specialized skin cells called chromatophores, enabling them to rapidly change their color and pattern to match their immediate surroundings, making them virtually invisible to unsuspecting prey.
These fish bury themselves partially or completely in the substrate, leaving only their eyes exposed. This behavior is aided by the migration of one eye during their development; they are born with an eye on each side of their head, but as they mature, one eye moves to the other side, allowing both eyes to face upwards as they lie flat. Once prey, such as a small fish or shrimp, comes within striking distance, the flounder launches an attack, engulfing its meal with a quick gulp. They position themselves facing the current, waiting for food to be carried past them.