Stay in SchoolsBy Kathy Kranking
For some fish, schooling is a smart way to survive.
Look—a school of golden sweepers is heading right toward you. But now the ones in front are turning, and, in just a split second, the ones in back will follow them. Right, left, up, down— no matter where they’re going, fish in a school really stick together! There are lots of good reasons for fish to stay in groups.
To a predator, this shimmery ball of scads may look like one giant fish. It can be hard to pick a single scad out of the crowd. But if a predator does attack, as the sailfish is doing above, being in a school means there’s a good chance that “the other guy” will get caught.
Cownose rays are known for migrating, or traveling, in large schools to warmer waters each year. As many as 10,000 may school together!
That’s a lot of rays. But believe it or not, some kinds of fish schools have millions of members. A school doesn’t have to be big, though. Even just a few fish can be a school. The fish that make up a school are all the same species. Some kinds of fish spend their whole lives in a school. Others form schools just at certain times, such as after hatching.
The schools of some fish, such as the sweetlips at left, move along in loose groups at a relaxed pace. But others zip around quickly, with the fish barely a fin’s length apart. They change course in the blink of an eye, but they never run into each other. How do they do it? One way is by being copycats. Fishes’ eyes are on the sides of their heads, which makes it easy for them to watch each other and copy each other’s movements.
Besides using their eyes to help them school, fish use their lateral (LAT-ur-ul) lines (see thin, dark line on fish above). These are rows of tiny cells that run along a fish’s head and body. The cells let fish feel their neighbors’ movements in the water. Then the fish move the same way.
Schooling fish may also tell each other which way to go. Of course, a fish can’t shout, “Turn left!” But some kinds of fish can talk to each other with clicks or other signals.
These hungry parrotfish are scraping algae (AL-jee) from coral with their sharp, parrot-like beaks. Staying in a school can be a good way to get help finding food. The more eyes there are looking for something to eat, the better the chances are of finding it.
Sometimes schools of predator fish even use teamwork to catch food. For example, they may herd smaller fish into a group, and then take turns darting in to grab a meal.
Some schooling fish have markings that help disguise them. When these butterflyfish swim together, it can be hard for a predator to tell where one fish ends and another begins. The fishes’ eyes are hidden in stripes, and their body patterns blend together.
Another kind of butterflyfish has fake eye spots on its tail, as well (above far left). That may trick a predator into attacking the “wrong end,” where it might do less damage.
Schooling can make it easier for fish to find mates. Instead of searching alone in the ocean, fish in schools are surrounded by many possible mates to choose from.
Scalloped hammerhead sharks are one of the only shark species that school. At certain times, they form large schools of mostly females, which makes it easier for males to come along and choose mates.
After all this schooling, you can see why schools rule!
“Good Reasons to Stay in Schools” originally appeared in the September 2014 issue of Ranger Rick magazine.
(Click on each image above for a closer view of the story.)