It’s back-to-school week for kids in Connecticut. School days never end, however, for many of the fish in our freshwater lakes and in Long Island Sound and the ocean beyond.
One online source says that one-fourth of all fish species spend their entire lives in a school, and that another 50 percent will swim in a school during part of their existence.
Kids go to school to learn. Fish swim in schools for a number of reasons. Here are four.
The first (and probably primary) advantage for fish to school is that there is safety in numbers. When a fish swims in a school, its familiar individual outline is no longer obvious to a predator, which instead sees a large mass. As the school changes direction and speed, these movements alter colorations – shiny one moment, dark another, as light reflects off the schooling fishes’ scales. That, too, may make it harder for a predator to single out an individual fish to pursue.
Another strategy for schooling is that it increases the odds of finding food. Would you fare better in a scavenger hunt or trivia contest by yourself or in a team? (The downside of hunting as part of a school, of course, is that, when food is found, there may not be enough to go around.)
Third, schooling with your own species improves your odds of successful reproduction. (Many species only come together in schools when it’s time to mate.)
And, finally, researchers have figured out that swimming together in a group makes it easier for fish to … well, swim. Sort of like how race-car drivers “draft” behind another car to reduce air resistance, fish in a school use less energy than each would expend by swimming off alone.
Researchers also have tried to figure out how fish swim within a school; how they move together so deftly better than the best Olympic synchronized swim team. The answer seems to be something called “optomotor reaction”; that each fish watches a spot or stripe on its neighbor and can reflexively move to follow that spot or stripe – and that each fish also responds to impulses felt on a sensory organ down its side called its lateral line.
Examples of schooling fish in Long Island Sound include menhaden, bluefish, striped bass, weakfish and herring. And the Aquarium currently is exhibiting a school of alewives, which historically “ran” up Connecticut’s rivers each spring.
Schooling isn’t a perfect strategy. As we’ve seen in several IMAX movies shown at The Maritime Aquarium, predators can work together to attack a school. Dolphin and sharks will surround a school near the water surface and work it into a tightly revolving mass called a “bait ball.” The predators then dart in with mouths open, often until there’s nothing left but a snowfall of scales.
Schooling also has worked to the advantage of the ocean’s most dangerous predator: humans. Ever-improving fisheries technology has made it easier for fleets to find and efficiently harvest fish in great numbers, especially when they’re massed together in a school. This has led to many species of fish becoming “overfished.”
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But WHY is a massing of fish called a school? The word comes from the Middle Dutch word schole, which meant a group of fish or other animals and was pronounced like school. (The word school – which we use today as a place of learning – has a different origin; it comes from the Latin word scola.)
