European flounder
The European flounder is a widely recognized species of flatfish, characterized by its flattened body and unique eye placement, with both eyes on one side of its head. This adaptable fish inhabits various aquatic environments, including freshwater, saltwater, and brackish waters, and is commonly found along European coasts, ranging from Norway to North Africa. Typically residing at depths of up to 175 feet, the European flounder can migrate significantly upstream into rivers and lakes.
Growing up to 20 inches long and weighing between 6 to 7 pounds, the European flounder utilizes its capacity for color change to blend in with its surroundings, aiding in camouflage against predators. Its diet primarily consists of mollusks, shrimp, and young eels, using powerful teeth to crush the shells of its prey. The species reproduces by releasing millions of eggs, which float to the surface and hatch within about a week. The life cycle includes a notable metamorphosis where the left eye migrates to the right side, transitioning it into a right-eyed flounder. Although popular among sport fishermen, the European flounder has little commercial value, leading to minimal threat from fishing industries. Its lifespan is estimated to be around 15 years, although some relatives in its family can live much longer.
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European Flounder
The European flounder is a familiar species of flatfish. This flat-bodied fish has both eyes on one side of its head and lives on the bottom, where it camouflages itself by changing colors. It is a popular sport fish but has no value for commercial fishermen as do other species of flounders and flatfish.
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Pleuronectiformes
Family: Pleuronectidae
Genus: Platichthys
Species: Flesus
The European flounder is one of the most common and adaptable flatfish species. It can survive in freshwater, saltwater, and brackish water, where the other two types of water meet. It is often in coastal waters from the tidal lines to 175 feet (52 meters) deep but may migrate as far as 40 miles (65 kilometers) upstream to lakes and rivers. It is native to Europe's coasts and ranges north to Norway's arctic waters and south to North Africa.
This fish belongs to the order of fish called Flatfish and the flatfish family called right-eye flounders. It has a flattened body which lies on the bottom of the water. Its eyes and mouth are on the top side of its body. An adult European flounder measures up to 20 inches (50 centimeters) long and weighs six to seven pounds (2 1/2 to 3 kilograms). Long fins with soft rays along the edges of its body ripple in wave-like motions so the fish can swim on the flow of the tides. It is a poor swimmer but can swim if necessary. It mostly floats on the currents. If threatened, the flounder may take water into its mouth and release it in a jet from the gill slits on its underside. This causes the fish to rise from the bottom so it can swim away.
The flounder can change the color of its top side so it camouflages against the bottom. On sand, it is tan, but on mud, it is brown. A gravel bottom results in the flounder having spotted skin. Some flounders have even been able to look like checkerboards. All these changes take several days. The flounder often buries itself in the bottom until the change is completed. The fish's underside is generally white.
The diet of a European flounder consists of mollusks, shrimp, marine, or saltwater, worms, and elvers, or young eels. It has powerful teeth for crushing the shells of its prey. During low tide, the flounder's prey rests in the mud and sand. At high tide, the prey begins feeding on plankton which are easy for the flounder to catch. One threat to the European flounder is sport fishermen, but the fish faces no danger from commercial fishermen since it has no value at fish markets.
Between January and July, the female European flounder releases up to two million eggs, which the male fertilizes. This process is known as spawning. She releases the eggs at depths of 80 to 130 feet (25 to 40 meters), but the eggs float to the surface and hatch after 6 to 11 days depending on the temperature. They feed on plankton, and when they are about 1/2 inch (one centimeter) long, they metamorphose, or change. In this metamorphosis, the eye from the left side of its body moves next to the right eye. This makes it a right-eyed flounder. It is an adult after three or four years.
The life span of the European flounder is not known for certain but is estimated at around 15 years. Other members of the family may live 25 to 40 years.
Bibliography
Dias, Ester et al. “Habitat Use and Food Sources of European Flounder Larvae (Platichthys Flesus, L. 1758) across the Minho River Estuary Salinity Gradient (NW Iberian Peninsula).” Regional Studies in Marine Science, vol. 34, 2020, doi:10.1016/j.rsma.2020.101196.
"Flounder." North Western Inshore Fisheries and Conservation Authority, www.nw-ifca.gov.uk/managing-sustainable-fisheries/flounder. Accessed 15 Apr. 2024.
Spencer, Erin. "Fast Facts about Flounder." Ocean Conservancy, 16 Dec. 2022, oceanconservancy.org/blog/2022/12/16/fast-facts-about-flounder. Accessed 15 Apr. 2024.