Good reasons to stay in schools… - why fish form schools - includes related information

Ranger Rick, Dec, 1994 by Kathy Walsh

You've probably heard this joke: "Why are some fish smarter than others?" The answer is, "Because they hang out in schools."

But schooling is no joke - for some fish, it really is the smart way to survive.

A school of fish can have just a small number of members - or it can have more than a million! The fish in a school are usually the same species (kind). Some species of fish live in a school almost all their lives. Others form schools only at certain times, like right after they've hatched.

A school can be made up of fish that just hang around together. But many schools are very organized, like this school of French grunts (see photo at left). The fish swim barely a fin's length away from each other. And each fish in the group moves at the same speed and in the same direction as the others. In the blink of an eye, a whole school will swim right, left, up, down, or even make a U-turn - all at the same time. It's kind of like a fishy marching band!

TRICKS OF THE TRADE

How do the fish move like that without swimming right smack into each other? One way they do it is by being copycats. Each fish watches its neighbors and copies every move they make - quickly! Meanwhile, the neighbors are copying their neighbors, and so on. So the whole school makes the same moves, and there aren't any crashes.

Besides using their eyes to help them school, fish also use something called lateral (LAT-ur-ul) lines. These are sensitive places along the fish's sides where they can feel their neighbors' movements in the water. Then the fish make the same movements.

Schooling fish may also tell each other which way to move. Of course, a fish can't shout, "Turn left!" But some kinds of fish can talk to each other with clicks or other signals.

So why do fish swim in schools? Lots of reasons. The main one is to stay safer from enemies. When there are lots of fish swimming together in a school, it's hard for a predator to pick out a single fish to attack, so it may not try.

But some predators will swim right through a school anyway and catch some fish, as this manta ray is doing (right). The more fish there are in a school, though, the better the chances are that "the other guy" will get caught. So usually a fish is still safer in a school than swimming alone.

BREAK IT UP

When a school of fish runs into an enemy, it sometimes separates into two groups that flow right around the predator. Then the groups join together again as soon as they've passed the enemy.

The school of fish above is treating a photographer as an enemy. The group is parting to swim around the photographer as he takes their picture.

But the photographer isn't their only problem - chasing after them is a hungry sea lion. So they'd better swim fast! Fish in a school face "tests" like these every day.

Why else do fish school? Another reason is that it's often easier to find food by schooling. The more fish there are looking for food, the more likely it is that they'll find some. Hundreds of pairs of eyes can spot food far better than one pair could.

Even some large predators form schools to hunt for food, as these rays (above right) and hammerhead sharks (below right) are doing.

THE BUDDY SYSTEM

Sometimes a school of fish will find food by hanging around with a "buddy." This school (left) is swimming along with a sand tiger shark. When the shark finds food and tears it apart, scraps are usually left over. So the fish stay nearby to feed on those scraps.

There are still other reasons that fish school. They may school to find mates. Or some kinds may gather together to migrate (travel from one place to another).

GANGING UP

Sometimes fish that school have a home area. For example, these anthias (left) have claimed a part of the coral reef to feed in. One of these small fish might not be able to defend the area on its own. But as a group, the school can keep away fish that are bigger than they are.

And that's just one more reason that schooling is a smart way to survive!

Too

Close

For

Comfort

Fish that school really stick together. These anthias (right) have followed each other into a hole with a hungry moray eel in it. Why? The small fish most likely dashed into the hole to hide from the photographer who took the picture. Right now the moray may be too surprised by the photographer to go after any of the little fish. But they'd better not stay there long!