Pleuronectes platessa Linnaeus, 1758, European seas.
OTHER COMMON NAMES
English: European plaice; French: Plie d’Europe, carrelet; German: Scholle; Spanish: Solla europea.
Dextral flatfish with a deep, oval body; a relatively large head; large eyes; a small mouth; and a series of four to seven bony knobs on the head along a curved line from the eyes back to the lateral line. Teeth are best developed on the jaws of the blind side. Strong, molariform pharyngeal teeth are present on the gill arches. Lateral line is curved slightly above the pectoral fin. Scales are cycloid on both sides of the body. Distinctive ocular side coloration, consisting of a uniformly brown background with brilliant red or orange spots. Blind side usually is uniformly white. The species can reach lengths to about 39.4 in (100 cm) and weights up to 7.9 lb (3.6 kg), but most adults average only about 13.8–19.7 in (35–50 cm) and weights of about 2.2 lb (1 kg). Individuals can reach at least 30 years of age, but most are much younger. Females grow faster and live longer than males, which rarely live longer than 10–12 years.
Northeastern Atlantic Ocean in marine and sometimes estuarine waters from the White and Barents Seas southward to the North Sea, including the British Isles and western Baltic Sea; off Iceland; occasionally off Greenland; and along the European coast from Germany and Denmark south to Spain and Portugal and in the western Mediterranean Sea.
Usually found on the inner continental shelf from shallow waters to about 656 ft (200 m) but most abundant in 33–164 ft (10–50 m); usually occur in waters of 35.6–59°F (2–15°C). Most commonly found on sandy sediments but also occur on mud or gravel bottoms. Newly settled plaice recruit to inshore waters typically between 9.8 and 88.6 ft (3–27 m), and sometimes juveniles are found in sandy intertidal pools. Plaice can tolerate reduced salinity levels but do not usually penetrate estuaries to any great degree and are not typically found in freshwater reaches within estuaries. During their first year, young plaice generally are found in shallow waters. By their second year, they begin to move to deeper waters. Older and larger plaice tend to live deeper than smaller and younger plaice.
A diurnally active, benthic fish that lies partially buried when possible. Plaice remain stationary for long periods of time, lying partially buried in the sediment. They are often active at night, especially in shallow water, and have been reported to exhibit homing
, at least in near-shore environments. Where there are tidal currents, the plaice orientates itself by pointing into the current and retains its position by pressing its dorsal and anal fins against the bottom. Many individuals congregate in the same general area. Plaice, including larger individuals, sometimes move on rising tides into intertidal areas to forage, retreating with the receding tide.
FEEDING ECOLOGY AND DIET
Opportunistic, visual predators that feed mainly during daylight hours. After metamorphosis, juvenile plaice consume small polychaete worms and harpacticoid copepods, but with increasing size their diet broadens to include a wider variety of prey, such as small crustaceans, amphipods, cumaceans, and small mollusks. Larger plaice consume a greater proportion of thinshelled bivalve mollusks, especially the siphons of burrowing species (which they nip off using the teeth of their blind-side jaws), as well as gastropod mollusks, shrimps, small crabs, and various polychaete worms. Feeding activity varies with season (temperature), with higher feeding rates occurring during warmer periods than during wintertime. The plaice takes its food in a nearly horizontal position, with its head raised slightly off the bottom. Predators that consume plaice include sculpins, lumpfish, spiny dogfish, weaver fish, seals, and cormorants. Shrimps and ctenophores prey on plaice in the early-life stages.
Maturity schedules vary, depending upon the area where the fish live, their food supply, and ambient temperatures. Female plaice reach sexual maturity between three and seven years of age (11.8–15.7 in, or 30–40 cm) and males at two to six years of age (7.9–11.8 in, or 20–30 cm) in the North Sea. Plaice spawn throughout their range, usually on well-defined spawning grounds. The spawning season varies with latitude and location but usually occurs in the early months of the year throughout its range (December to March in the North Sea, February to March off Denmark, and March to April off Iceland), when water temperatures are about 42.8°F (6°C). Mature fish may undertake extensive migrations from feeding grounds to discrete spawning grounds. The extent of migration depends upon the individual stocks. Spawning grounds generally are located at depths of 66–131 ft (20–40 m). Males and females may pair up and swim one above the other during spawning. Plaice do not guard a nest but rather scatter eggs, which may number up to 50,000 during a spawning event. Eggs are planktonic at first, gradually sinking as development proceeds. Hatching occurs in 18–21 days, depending on temperature. The larval stage lasts between four and six weeks, after which the fish metamorphose at about 0.4–0.7 in (10–17 mm) in length.
Not threatened, although stock sizes have declined over time as a result of overfishing, habitats destruction, and pollution.
SIGNIFICANCE TO HUMANS
One of the most familiar flatfishes in northern European waters, highly desired owing to its size, abundance, and edible qualities. It is the single most important commercial flatfish to the fisheries of Europe. The species also is targeted by a large recreational fishery. Plaice are considered a potential species for aquaculture and are kept as an aquarium species.
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