The whys and hows of a fish’s favorite group activity.

Story by Suzanne Gerber ~ Photos and Captions by Barbara Shively

“United we swim, divided we fall prey” might be how a fish would paraphrase the well-known American sentiment (which was not, for the record, originally uttered by the 16th president, though it was he who most famously used it). When birds do it, it’s called a flock. When bees do it, it’s called a swarm (or a colony). Land animals herd. And when fish congregate, it’s called a school.

Some species, like the piranha (which thankfully we don’t have in Turks & Caicos), are born into schools and spend their whole lives in them. But the vast majority of oceanic fish – researchers guess 80% of the 20,000+ known species – spend only part of their adult lives in school. What exactly is a school, you might be wondering? Most simply put, it’s a group of same-species fish that live, swim, hunt and reproduce together. (Note that the correct name for a cohesive group of marine mammals, like whales, dolphins and seals, is pod.) A school moves in harmonious patterns throughout the oceans, sometimes giving the impression that it is one single, terrifyingly ginormous fish. And that’s precisely the point.

Safety in numbers

Just as with humans and elsewhere in the animal kingdom, pluribus is typically safer than unum. Even a ferocious (and hungry) predator will be scared to bite into a snack that’s several times its size. A large, tight school can be truly formidable. And from the schooling fish’s perspective, it’s easier and safer to hide behind another creature that looks exactly like you (and maybe even a little more appetizing). In reality, the unlucky fish positioned on the outside of the school are more at risk of being eaten than those in the center. Leveling the playing field is the fact that schooling predatory fish also benefit from their school ties because when they hunt in larger numbers, they increase their odds of success. The big downside of schooling for all fish is that many of the bipeds in the fishing industry study school behavior and use that knowledge to catch large numbers of certain species of deep-water fish, like tuna, at a time.

Dinner for 800?

Beyond the obvious protection schooling offers, the behavior also helps the group find their own dinner. If you think two heads are better than one, how about 800? Also, schooling helps insure reproductive success – a larger “drop” statistically increases the odds of eggs escaping predation.

And then there’s the energy-saving aspect (poetically referred to as the slime factor). Fish do emit a slight slime, designed to reduce the water friction along their bodies and allow them to conserve energy when swimming. And when fish do their synchronized swimming – in well-choreographed patterns – their tails create mini currents, or “vortices” (think whirlpools). Each fish can theoretically use its neighbor’s tiny vortex to reduce the water friction on its own body.

Define your terms

So how many fish comprise a school? While there’s no upper limit, scientists tend to agree that it takes at least four to six members of the same species to create a comfortable school. As noted above, most fish (particularly saltwater fish) aren’t born into schools, but rather learn or develop the behavior. As juveniles, they usually stay near one parent, but as they mature, members of most species start to swim in pairs, gradually growing their numbers until they’ve formed a cluster and eventually the classic “parallel” schooling pattern.

I was a relative youngster myself (using the term loosely) when I had my first spectacular fish-school experience. I wasn’t yet a diver, just a newbie snorkeler, and I was spending a few days on Ambergris Cay in Belize. The dive boat dropped me off on a shallow reef and left me to my own devices for the better part of an hour. A tremendous school of blue tang just happened to be taking its daily constitutional, and I wanted desperately to be a blue tang. So I hovered above them while they meandered this way and that, like one enormous blue flag rippling in the current. I tried to discern the leader, to find the point of origin from which this astonishing connected movement emanated but I couldn’t. It was magical and mystical, a silent ballet. A few discrete streams of fish converged, eventually building to (I estimated) a thousand individual fish. Every so often I’d freedive down to take a closer peek, but that just served to cause a mass gyration away from the giant, graceless humanoid with the oversize green feet. But for the better part of an hour, they allowed me to be a part of their school, and it was amazing.

I’ve also seen massive schools of giant barracuda in the wider Pacific – cyclones of fish rising hundreds of feet in the water column. I have a photo of a fellow diver just a few yards away from the “cuda ball,” and this 6-foot, 200-pound guy looks like a smudge on the page next to that teeming mass of marine life. Another time, off the Pacific coast of Costa Rica, we kicked back on the sandy bottom at about 60 feet and looked up. Just beneath the surface a school of perhaps 500 horse-eye jacks was mingling with a school of at least that number of cuda. They swirled like whorls of paisley fish, and it was a sight I’ll never forget.

Sixth sense?

OK, so we understand why fish school, but the question remains: How do they do it? One tool is sight, which begins to function immediately after birth (to enable feeding).  Because their eyes are situated on the sides of their head, fish cannot focus directly forward, just laterally, which happens to be particularly useful for schooling. Fish can see what their mates are up to and react accordingly.

But their truly amazing quality is the ability to sense water displacement, thanks to tightly packed bundles of protruding hairs, called neuromasts and which are similar to those in the human inner ear. While these hairs are present all along a fish’s head and body, they are concentrated along the fish’s side, or lateral lines. It only takes the slightest change in pressure (e.g., a photographer moving her camera within shooting distance) for the hairs to bend. That’s why fish are such gifted escape artists.

As hard it is for humans, whose brains thrive on order and patterns, to understand, there really aren’t leaders in the school coordinating all the movements. Each fish simply responds to the movements of the other fish, as well as to outside movements. Like birds, or members of other herds, fish seem to be similarly attuned to danger and able to exhibit “group think.”

There’s a lesson in this for us homo sapiens, and it goes back to the opening conceit: that we are never stronger than we are when united. And never has there been a time in recent history when setting aside our trivial differences and acting as a world truly united is the most important thing we can learn in any kind of school.

New York-based Suzanne Gerber writes about scuba, travel and health for a variety of publications. Book your next dive trip by contacting Suzanne at suzanne@worldofdiving.com.

Avid underwater photographer Barbara Shively discovered Grand Turk diving in 1997 and has returned every year. It is her passion to share the coral reefs’ beauty through her photographs, many of which can be viewed and purchased at http://shivelygallery.com/. A variety of her prints are on sale at Art Provo, located in The Regent Village, Providenciales.