学进去

It would be difficult to find one herring (鲱鱼) swimming alone in the sea. Herring always swim in groups c1．schools. Sometimes hundreds of thousands of small, silvery herring swim together, covering the surface of the sea for miles.

In a school of herring, all the fish are about the same size and age. Since n2． of the fish is older or wiser than the others, there is no leader, or “teacher”. All the fish is in a school swim in the same d3． and at the same speed. When one turns, they all turn. When there is danger, the fish move closer together.

One 4． that herring swim in schools is that they are more protected from danger. Herring have no defense weapons (防卫武器) to use a5． their many enemies in the sea. When they crowded together, the fish inside the group are p6． by the bodies of the ones on the outside. A school of close swimming herring may look like a s7． , giant fish. Some enemies may be frightened away by the large shape.

As the herring g8． larger, the school is attacked by larger, hungry fish. Each time some herring are lost, but many survive. The survivors stay t9． in smaller schools or join another school of herring.

Female herring do not lay eggs u10．they are three or four years old. Each mature fish can lay as many as 40000 eggs. From these eggs come some new schools of herring to replace the disappearing older schools.