Shoaling versus schooling fi sh

ENVIRONMENT

“ Large schools of fish can also confuse an attacker by making it difficult for it to single out its prey”

Shoaling versus schooling

Discover how and why fi sh stick together as they travel the oceans

Agroupofhundredsorsometimes thousands of fi sh swimming in unison is one of the most spectacular sights in nature, but what is the reason for this incredible phenomenon?

First, it is important to understand the subtle difference between shoaling and schooling. A shoal is a social group of fi sh swimming closely together but foraging for food individually. Those shoals can consist of different species and sizes of fi sh. A school of fi sh swim in a more synchronized fashion, moving at the same speed and turning simultaneously. These groups often consist of a single species.

Some species, including tuna and herrings, are obligate shoalers, meaning they spend all of their time either shoaling or schooling. Others, such as Atlantic cod, will only shoal some of the time, often when they are looking for a mate.

In addition to reproduction, there are several other reasons why fi sh congregate in shoals or schools. One is that it gives them the advantage of safety in numbers, as being part of a group reduces the chance of a fi sh being eaten by a predator. Large schools of fi sh can also confuse an attacker by making it diffi cult for it to single out its prey or even scare the predator off by resembling one large fi sh.

Another benefi t is that several eyes are better than one, and so a shoal of fi sh is much quicker at spotting food or a potential predator than one fi sh is on its own.

Scientists also believe that swimming in unison gives the fi sh more hydrodynamic effi ciency, as the beating of the front fi sh’s tail helps to propel those in its wake.

DID YOU KNOW?

Shoaling reduces stress, as a solitary fish’s heart rate is often much faster than that of a fish in a shoal

Fast-moving schools typically form a wedge shape, while feeding schools are usually circular

How fi sh swim in unison

Schools of fi sh move very quickly and can change direction at a moment’s notice, yet the fi sh manage to never break formation or collide. Their fast reaction speed allows them to instantly copy the movements of the fi sh next to them, which they can see thanks to the position of their eyes on the side of their head.

Vision plays a big part in a fi sh’s ability to school, as most schools become shoals when it gets too dark to see. However, many species of fi sh also have a lateral line down the side of their body, which contains cells similar to the hair cells found in the human ear. This enables the fi sh to sense changes in water currents, helping them to detect the movements of nearby fi sh when visibility is poor and keep a safe distance from them as they change speed and direction.

A shoal, such as this group of oriental sweetlips, has a looseformation