Biology of plaice & flounder

Plaice (Pleuronectes platessa) and flounder (Platichthys flesus) live in European waters. They belong to the group of flat fish (Pleuronectiformes) described as the order of ray-finned, demersal fish. The flatfish family includes over 500 species of which some of the well-known species are sole, dab and turbot.

Flatfish are characterized by their flat body squeezed from the sides. A flatfish does not lie on its belly – it lies on the side, with both eyes lying on the same side of the head. The flatfish has a normal round fish shape when hatched, but changes in the backbone transforms the shape to flat. The one eye then wanders around the head. In some families, e.g. the plaice, the eyes are always on the right side of the body (dextral or right-eyed flatfish), and in others, they are always on the left (sinistral or left-eyed flatfish). The flounder is closely related to the plaice, but is most often left-eyed.

Plaice predominantly reside in the North Sea, but is found from the Mediterranean to the Barents Sea. Flounder is predominantly found further east in the Baltic Sea and in areas with lower water salinity. Plaice and flounder both live near the seabed, they are so-called ‘bottom-dwellers’, using sand as camouflage. In that environment, it is practical to have both eyes next to each-other so they have a full outlook while hiding on the seabed. Flounder feed on a variety of invertebrates and fish, whereas the plaice is known to feed on thin-shelled clams and bristle worms.

Plaice in the North Sea spawn in the first quarter of the year and is primarily caught in the summer months from May to October when they are finished spawning and have the best meat quality. Flounder spawn later in the year and the primary catching season runs in wintertime from October to March.

In terms of processing, the two species complement each-other perfectly, since the catching seasons in large part replace each other. Based on close cooperation with the fishermen, the fish can be landed fresh year-round and fileted directly on the same lines for optimal product quality. 

Fishery

Royal Greenland is the largest single buyer of plaice from the northern part of the North Sea, subarea IV, where the Danish part of the fishery is certified sustainable against the Marine Stewardship Counsil (MSC) environmental standard for sustainable and well managed fisheries. Royal Greenland purchases plaice on all auctions along the Danish west-coast during the main fishing season from May to October.

Plaice can be caught using different tools, North Sea fishery is dominated by set net, Danish seine and demersal trawl. The main fishing nations for plaice are The Netherlands, United Kingdom and Denmark. In the Dutch fishery for plaice, taking place in the –mid and southern parts of the North Sea, mixed fishery targeting various species, including sole, is used. This means using a net mesh size of down to 80 mm, which catches plaice under landing size of 27 cm, resulting in considerable discard rates (44% by weight in 2012). Further north, the plaice is the main target species for the fishermen for which reason the mesh size of the nets are 100-120 mm depending on the area, leading to significantly lower discard rates. (Source: www.ICES.dk) 

Flounder is caught with demersal trawl primarily in the Baltic Sea in a mixed fishery with cod – where flounder is often perceived as by-catch. Due to a tradition for high discard rates, Royal Greenland has taken the initiative to work directly with a number of fishermen who land their catch for direct distribution to our factory in Koszalin, Poland. Contracts ensure correct handling and quality of the flounder and no discard in the fishery. The contracts with the fishermen have proven to be a great success as Royal Greenland obliges to buy the full catch while the fishermen undertake the obligation to handle the fish according to a defined quality procedure.

Eating quality

“No summer in Denmark without fried North Sea plaice and freshly dug potatoes, and no Christmas lunch without breaded plaice or flounder with “Remoulade” sauce” – both plaice and flounder are well-known and popular edible fish in especially the north European kitchens and are used in a wealth of dishes. In Sweden, it is served with dill and lemon, in the UK it is often eaten battered or fried and in Germany it often served with shrimp on bread or with a potato side dish. Further south the plaice is also appreciated in e.g. the Italian kitchen where it is often served lightly dusted with flour and garnished with tomatoes and herbs.

Like other flatfish plaice and flounder can be prepared in many different ways, they can be pan-fried, deep-fried, baked, boiled, dried or smoked. The two fish types also work as good substitutes for other members of the flatfish family and can be used in dishes designed with e.g. sole or turbot.

Both plaice and flounder have white, firm meat and a mild, fresh flavor. Both fish types are low in fat and with a good level of minerals, especially selenium and iodine.