Because plaice are widely available in shops and restaurants, it is easy to think that there is an inexhaustible supply. But the plaice is no longer a fish that anglers can catch regularly.
They are still fairly common around British shores but – like any other fish species in demand for the table – they are under considerable pressure from fishing fleets.
Unlike skates and rays – species which are flattened from top to bottom – the plaice in fact swims on its side. The mottled brown top surface is really the right side while the pure white underneath is the fish’s left.
Colouring varies from brown to grey because the plaice is able – chameleon-like -to match the colour of the sea bed. The small red or orange spots on the top side appear on plaice from any habitat. The skin is smooth though there are small ridges on the head which distinguish it from other flatfish species. The lateral line is slightly arched.
Life for the young plaice begins with spawning time during January or February in depths of 27-55m (90-180ft). The eggs – about 2.5mm in diameter – float in the sea. Up to a quarter of a million eggs can be produced by one 1.5kg (3Xilb) female. The eggs hatch in 10 to 30 days depending on water temperature. Newly hatched larvae measure around 8-9mm long.
Plaice look like any other fish at this stage — being rounded rather than fiat. But when the larval plaice is between one to two months old — and 10mm long — one eye starts moving around to join the other one. The young soon start to swim like adults, with their left side facing the sea bed. Being bottom-feeders, plaice only need to be camouflaged on one side.
Their early life is spent feeding on microscopic plankton, until they can graduate on to small cockles and mussels.
Growth is fairly slow. Plaice take four years to reach 30cm (12in) in length. They are quite long-lived – a number of fish over 20 years old have been caught and it is likely that they could live for as long as 30 if commercial fishing were less intensive.
They reach maturity between their second and seventh year; the males are normally a year behind females in development.
Plaice move seasonally from their deeper spawning grounds, reaching the shallows in spring and summer. In shallow waters they feed mainly on bivalves such as mussels, razorfish and cockles. The smaller organisms are swallowed whole, the shells being crushed by powerful throat muscles and pharyngeal teeth.
Their preferred habitat is sandy or pebbly bottoms, but they also inhabit areas where rocky ground is interspersed with sand. Here mussel beds are common – a major attraction for plaice. Camouflage is essential in such beds, where large predators often lie in waiting.
Plaice are particularly active at dusk. Smaller ones can sometimes be found in estuaries where they may be confused with dab and flounder.