Japanese Flounder: A Fascinating Flatfish
This fascinating flatfish undergoes a profound transformation, adapting for a life of camouflage on the ocean floor where it is both predator and prized catch.
The Japanese flounder (Paralichthys olivaceus) is a temperate marine flatfish with significant economic and cultural value in East Asia. Known as “hirame” in Japan and “gwangeo” in Korea, it is a prized finfish in both wild-caught and aquaculture markets. Its popularity stems from its rapid growth and desirable taste.
Distinctive Biological Features of the Japanese Flounder
The Japanese flounder’s most striking feature is its asymmetrical body, a characteristic of flatfish. As an adult, both eyes are on the left side of its head. This asymmetry is an adaptation for its bottom-dwelling lifestyle and develops during a metamorphosis in its larval stage.
The flounder’s coloration provides effective camouflage. Its top side is an olive or brownish color with darker spots, allowing it to blend with sandy or muddy seabeds. The underside, which faces the seafloor, is white, helping the fish avoid detection by predators and prey.
Japanese flounders possess a large mouth with strong, sharp teeth. Adult fish can reach lengths of up to 103 centimeters and weigh 9.1 kilograms, though the average size in commercial catches is smaller.
Natural Habitat and Ecological Niche
The Japanese flounder is native to the Northwest Pacific’s temperate coastal waters, including Japan, the Korean Peninsula, and China. It prefers soft, muddy, or sandy bottoms on the continental shelf at depths down to 100 meters. Water temperatures in these habitats range from 21 to 24 degrees Celsius.
As a benthic predator, the Japanese flounder is an ambush hunter that lies in wait on the seabed. Its diet consists of smaller fish, crustaceans like shrimp, and other invertebrates such as polychaete worms. This feeding strategy is aided by its camouflage and a powerful, rapid strike.
The flounder is prey for larger marine animals, including other fish and marine mammals. Its primary defense is its ability to partially bury itself in the sediment.
Life Cycle and Development
The flounder’s reproductive cycle is influenced by water temperature, with spawning seasons varying by region. In southern Japan, spawning is from March to April, while in northern waters, it is from late April to July. The fish migrate to shallow waters to release their pelagic eggs, which float freely.
After hatching, the larvae are symmetrical, with an eye on each side of the head. They drift in open water for 24 to 50 days while undergoing metamorphosis. This process involves the migration of the right eye to the left side of the head and the flattening of the body.
Once metamorphosis is complete, juvenile flounders settle on coastal sandy bottoms and feed on small shrimp. As they grow, they move offshore and transition to a diet of larger prey. The growth rate is fast, and they reach sexual maturity within one to two years.
Significance in Cuisine and Fisheries
Japanese flounder, known as hirame, is an esteemed food fish in Japanese cuisine. Its flesh has a delicate, sweet flavor and a firm, tender texture, making it popular for sashimi and sushi. A valued part is the “engawa,” the muscle from the fin, which has a unique, crunchy texture.
Beyond raw preparations, hirame is also enjoyed cooked through methods like meunière, frying, or grilling. Its versatility and taste contribute to its high demand and significant economic market.
To meet high demand, the Japanese flounder is sourced from both commercial fisheries and aquaculture. Wild flounder are caught using methods such as trawling and gillnetting.
Aquaculture production has become a major source for the market. Japan, Korea, and China have large flounder farming operations, with Korea being a leading producer, which helps provide a consistent supply.