Wild Harris

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Flounder and Plaice are two very similar fish that live on sandy seabeds. They feed on small creatures such as shrimps and worms, but also like to bite off the protruding rear end of lugworms as they make worm casts as they rid of the sand they've been eating (the worms grows itself a new one!)

Flatfish have an unusual life cycle - they begin life as a normal looking fish, but as the grow older they rest on the seabed on one side. The upper side develops a dark, camouflaged colouration, while the underside becomes white. The eye on the underside wouldn't be much use looking at the sand all day, so it moves from the lower side to the upper side of the head, until both eyes are on the same side. This is important for the fish since, as a hunter, it needs to see its prey clearly and be able to judge how far away it is.

Flounders are perfectly camouflaged on a sandy seabed, matching the colour so perfectly that they are almost impossible to see. When they come to rest they shake their fins so they are partially buried, casting no shadow to reveal their presence.

When it comes to camouflage, these flatfish are true masters. Not only do they match the colour of the seabed, they also attempt to mimic the general pattern of light and shade. This they do by sight - a fish with damaged eyes loses the ability to blend into the background. By opening and closing special colour cells in their skin they can match any background they find themselves on in an instant, changing from light to dark as they move from sand to pebbles. Despite the orange spots which are also present, the plaice is usually very hard to see, and like many animals with superb camouflage it seems to have complete faith in its ability to stay hidden Ð if approached it will lie perfectly still and only move away if it is touched.

Plaice are long lived fish, living to the age of 50 years or more if not caught, and can reach a length of well over a metre, although fish of this size are increasingly rare because of intensive fishing activity by humans.

Plaice    (Photo: Sue Scott)

Almost invisible against the sand, the orange spots on this flatfish indicate that it is a plaice. When lying flat it casts no shadow to give away its position.

Plaice    (Photo: Paul Tyler)

This plaice lies on a sandy seabed with scattered clumps of weed.

The fish changes its skin colour to mimic the seabed, even the weed clumps! 

Plaice    (Photo: Paul Tyler)

The plaice is a right-sided flatfish - its left eye has moved around its head until it joins the other eye on the right side. Without this adaptation it would have the use of only one eye, and would not be able to hunt so well.

Flounder    (Photo: Sue Scott)

The flounder looks very similar to the plaice, but lacks the orange spots.

This particular flounder is living on a mixed seabed of sand, shells and pebbles, and has changed its skin colour to mimic the seabed type. Were it to swim to a sandy area it would change its colour to match the sand in a few seconds. This is done by expanding or contracting special pigment cells in its skin until it matches what the fish sees with its eyes. A blind plaice or flounder is unable to match its background.

Flounder    (Photo: Paul Tyler)

Spot the flounder! When a flatfish lands on sand it gives a little 'shiver' which covers it in a light dusting of sand grains. Combined with a perfect colour match, the fish is, as you can see, almost invisible (if you look carefully you can see the edge of its lower fin and its tail - the fish is facing away from you). 

by Paul Tyler

Link to Shore Animals

Link to Soft Seabed Animals