Understanding Schooling, Shoaling, and Why Group Size Matters

 

Why Do Fish School?

Schooling fish are some of the most popular fish for community aquariums, and tetras are probably what most people picture first. There are plenty of others, though, including rasboras, danios, minnows, rainbowfish, ricefish, and even fish like Corydoras that spend most of their time near the bottom. They don't all group together in exactly the same way, but being around others of their own kind is an important part of how many of these fish naturally live.

There is a reason for that. In the wild, a small fish by itself has to pay attention to everything happening around it. In a group, there are more fish watching for danger, and one fish reacting can quickly alert the others. Being part of a larger group can also make it harder for a predator to single out one individual. Schooling and shoaling can help with finding food and give fish the opportunity for the normal social interactions that happen between members of their own species.

Those instincts don't disappear when we put the fish in an aquarium. There may not be a predator waiting behind the driftwood, but the fish doesn't know that the way we do. Keeping a naturally schooling or shoaling species with a proper group gives it the opportunity to behave more like it would naturally.

Schooling and Shoaling Are Not Quite the Same Thing

We use “schooling fish” pretty loosely in the aquarium hobby, although a lot of what we see in our tanks is actually shoaling. Shoaling fish stay together socially, but they don't necessarily spend the entire day swimming in the same direction as one tight group. Schooling is the more coordinated behavior we see when the fish tighten up and begin moving together.

The same group of fish can do both. A comfortable group of tetras may spread out through the aquarium to explore and feed, then quickly come together when something gets their attention. Seeing them spread out isn't necessarily a sign that you've somehow failed to get them to school. In a secure aquarium, they may simply have no reason to stay tightly packed together all day.

FISH SPOTLIGHT: Ember Tetra

Ember Tetra (Hyphessobrycon amandae)

Ember Tetras are a good fish for watching the difference between schooling and shoaling. A comfortable group may spread out among the plants and then pull together when something changes around them.

Why Does the Number of Fish Matter?

This is where keeping schooling fish in groups becomes more important than simply liking the way a school looks. If a species naturally depends on interactions with its own kind, keeping one fish by itself takes those interactions away. Some fish become shy or spend more time hiding when kept alone or in very small groups. Others can become nervous, and normal chasing or social behavior may get directed at the same one or two fish over and over because there aren't enough members in the group.

A larger group spreads those interactions around and gives the fish more opportunities to behave normally. It can also change what we see from them. Fish that seemed timid in a very small group may spend more time out in the open once there are enough of their own kind around them. Of course, group size isn't the only thing that matters. The aquarium still needs enough room, appropriate water conditions, suitable tank mates, and places where the fish can feel secure.

Six Isn't a Magic Number

“Keep six or more” has become one of those phrases you see everywhere in aquarium care information. Six can be a reasonable starting point for some species, but there isn't a switch that flips when fish number six enters the aquarium. Different species have different social behaviors, and the amount of room available matters just as much as the number itself.

If an aquarium can comfortably support ten or twelve of a schooling species, that larger group may give you more of the behavior you wanted to see in the first place. In some setups, twelve of one species can also make more sense than six of one fish and six of another. We would rather look at the adult size and behavior of the fish, the available swimming room, and the rest of the stocking plan than treat six as a universal rule.

FISH SPOTLIGHT: Celestial Pearl Danio

Celestial Pearl Danio (Danio margaritatus)

Celestial Pearl Danios are a good reminder that social fish don't all form the classic tight school. They spend plenty of time moving through plants and structure in loose groups, with males displaying and fish interacting with one another.

Schooling Fish Are Not Just Tetras

Tetras deserve their reputation as great community fish. There are many species to choose from, they come in a huge range of colors and sizes, and plenty of them do very well in groups in community aquariums. The mistake is thinking that a schooling fish automatically means a tetra.

Rasboras give us another large group to consider, including some very small species that work especially well around plants. Danios can give us a much more active aquarium, while minnows include species that are comfortable at cooler temperatures than we would choose for many tropical tetras. Ricefish and medaka add still more choices and can work in setups that are very different from the typical tropical community aquarium.

Schooling fish aren't necessarily small fish either. Rainbowfish are a good example. A species such as the Boesemani Rainbowfish can reach several inches long and still benefits from being kept with a group of its own kind. They need considerably more swimming room than a group of small tetras or rasboras, but in a larger aquarium the group itself can become one of the main attractions.

There are larger barbs and other schooling fish that give us more options as well. The social behavior may be similar, but keeping a group of tiny rasboras and keeping a group of adult rainbowfish are obviously two very different stocking decisions. This is why we have to consider the space a group will need as adults and not just whether a species is described as a schooling fish.

Then there are Corydoras. They aren't going to form the same kind of school we see moving through open water, but they are social fish, and keeping a good group together lets us watch their interactions along the substrate instead. This is also a good reminder that not every fish that benefits from being kept with its own kind should automatically be called a schooling fish.

FISH SPOTLIGHT: Dwarf Neon Rainbowfish

Dwarf Neon Rainbowfish (Melanotaenia praecox)

Dwarf Neon Rainbowfish show a very different side of keeping fish in groups. They are active, visible fish that interact constantly, and a good-sized group can become one of the main attractions in an aquarium with enough swimming room.

Finding the Right School for Your Aquarium

Understanding why these fish live in groups is the first part. The next question is which schooling fish actually make sense for the aquarium you have. A small rasbora, an active danio, and a larger rainbowfish may all benefit from being kept in groups, but they don't need anything close to the same amount of space.

That's why the other articles in our Community Aquarium: Schooling Fish Guide Series look at aquarium size and start narrowing the choices from there. We can look at different families, group sizes, activity levels, temperatures, and where the fish spend their time instead of handing you one giant list of schooling fish.

Once you start looking beyond tetras, there are a lot of choices. The important part is choosing a group that has enough room to live together and giving the fish the opportunity to show the natural social behavior that made us want to keep a school in the first place.