Also, these flat fish have a wonderful way of changing colour.  Put them on light sand, and they become lightish.  Put them on dark sand and pebbles, and they soon match it by becoming brown and mottled.  This is a most useful dodge where so many enemies abound, all swifter in the water than the slow-swimming flat fish.

If you look for flat fish in an aquarium, you will not easily see them.  Now and again one will swim up, with a wavy motion of its body.  On settling again, it shuffles and flaps about, works itself into the sand, hiding its edges well under, and then, hey presto! it is gone!  If the flat fish are so hard to find in a tank, you may be sure it would be impossible to find them on the sea bed.  They are poor swimmers, but perfect hiders.

As far as we can tell, they feed on other living creatures.  The ocean floor is a huge dining table for them, where they find very mixed dinners.  They eat small fish, sand-worms, shell-fish, Shrimps and young Crabs.  The Plaice has strong, blunt teeth in its throat, and is well able to grind up the shells of Cockles and other molluscs, swallowing the juicy contents.

Now we have seen that the Plaice is first a floating egg, and then a tiny transparent “round” fish.  It sinks to the sea bed, lies on one side, and becomes a flat fish like its parents.

These little baby flat fish, not much larger than your thumb-nail, crowd in the shallow, sandy parts of the sea near the coast.  There they often end their lives in the shrimp-trawl, as we have already noticed.

After leaving this “infants’ school” the Plaice, and other small flat fish, go to deeper water.  There they feed and grow fat.  Our fishermen know where to find them.  Indeed, these special fishing grounds are so well known that flat fish are scarcer than they used to be.  Some kinds are much too dear ever to be seen on the poor man’s table.

There is a special net for catching flat fish, called a trawl.  This is a large net, dragged over the bed of the sea by ropes, or steel wire, attached to the sailing vessel or steam trawler.  The net is kept open under water by means of beams or boards.

When the flat fish are disturbed, they rise a foot or two from the sea floor, and are then swept into the gaping mouth of the deadly trawl.  Once in, there is no escape.  There they remain, pressed together, until the net is hauled up and emptied.

EXERCISES

1.  Give the names of five kinds of flat fish. 2.  How does the Plaice escape its enemies in the sea? 3.  What is the food of the Plaice? 4.  How are flat fish usually caught for the market?

LESSON III

SEALS

There are many different kinds of Seal; the family is a large one, but all have one thing in common—­the fish-like body, with toes joined together by a web.  Anyone who has seen the diving power of a Seal, and its wonderful way in the water, will agree that the “flippers” of the Seal are as useful as the fins of the fish.