Danio rerio with a missing right eye

How Many Danios Should be Kept Together: Tank Setup and Size

Danios are entertaining little fish. They love living in groups of 6-10 individuals who swim around like maniacs. Small as danios are, rarely exceeding two inches or four centimeters, they need ample space to play around, but also to establish peaceful hierarchies.

Indeed, the minimal tank size per danio is quoted as 10 gallons or 40 liters, but danios shouldn’t live alone. They feel best in schools of 7-10. 70-gallon tanks for danios, then? A 20-gallon will work well for up to six danios. If your tank is smaller, then reduce the number of danios to four or even three, if you have a 10-gallon tank.

The type of danio doesn’t matter as much as their size. Select fish of roughly the same proportions to give them a fair chance to establish a functioning society.

You should have at least six danios, in a long tank with open space. Danios swim in straight lines and like schooling. Groups of 7-10 danios are more likely to establish healthy school dynamics. Fewer fish can lead to the weakest being harassed too much but hiding space can alleviate the issue.

The most common species like zebra danios (Danio Rerio), pearl danios (Danio Albolineatus), and leopard danios (Danio Rerio var. Frankie) grow up to 5cm/2″. There are giant danios that grow twice as large as the rest, but I discuss the smaller varieties here.

Let’s see how many danios you can keep based on the tank size and setup.

Are Danios Peaceful?

Danios are good community tank fish. They are energetic and largely peaceful, given the right conditions.

In large enough groups, their playful aggression remains just a part of their natural behavior that is intrinsic to their schooling life. Groups reduce stress through socializing which makes them feel more secure.

In smaller groups or inadequate space, the abundant energy of larger danios can wear out smaller fish. I’ve seen them torment guppies the same size as slimmer danios.

Most danios, most of the time are peaceful, but there are aggressive individual fish every now and again. They could be isolated or given more company to compete with.

In a larger aquarium, the extra swimming space and hiding spots will balance things out.

Can Danios Fight with One Another?

Yes, danios can exhibit aggressive behaviors towards one another, especially if they are kept in small groups or in insufficiently sized aquariums. Danios are generally peaceful fish, but they can become territorial or aggressive if they feel stressed or if their social needs are not met.

Inadequate space, lack of hiding spots, or keeping them in small groups can lead to increased aggression. When kept in larger groups and provided with a spacious environment, the aggression tends to be minimized as they can establish their territories more easily.

It’s crucial to observe your danios and their behavior regularly. If you notice regular heavy aggression, such as nipping or chasing, you may need to increase the group size, rearrange the tank layout, or provide more hiding spots and plants to diffuse aggression and establish a more harmonious environment for them.

The latter should be done carefully as danios naturally hang out in open spaces. If you clutter a part of the tank with places to hide, the fish could cluster closer together in the remaining open space, increasing the odds of aggressive behavior.

How Many Danios Should Be in a School?

For danios, a school generally consists of at least six individuals. However, a group of seven or more will ensure more cohesive and harmonious school dynamics.

For the last eight months, I have had six danios in my 1 meter-long tank. Four zebras, one slim leopard danio, and one pinkish. For the most part, they’ve been exhibiting playfully-aggressive behavior occasionally, chasing around every now and again without any aggressive moves like nibbling or torpedoing. Other than the first couple of weeks, while a semi-stable hierarchy formed among them, their group has been lively and healthy.

And then about 10 days ago, the thin pink danio was lying on the bottom, breathing rapidly, clearly in shock. I was equally shocked to discover that it was missing an eye. The wound was fresh, still bleeding a bit, and the fish looked worse for wear.

A danio rerio with bloody right eye socket and no eye.

I thought the shock would kill it. I didn’t see who had plucked its right eye, but the largest danio was in a foul mood, chasing the smaller two of the group with powerful darting strikes.

It was feeding time and I thought food will make the attacker less likely to strike again. To my genuine surprise, the injured fish forgot most discomfort and went bravely in for the food too. Two weeks later Dan Sparrow looks healthy and almost normal. Most of the time, he swims slightly tilted toward his left side and mingles somewhat less often with the other danios. It may be the missing eye or the rum he consumes in the shade of Vallisneria leaves.

He is still social, though, and eats a lot. Doubt he is growing more at this point, but he is certainly giving it a go.

Next time I go to the fish store I am getting at least one new danio, though.

A School of Danios Enters into a Bar…

How many danios should be kept together? More than six.

They are cool fish, vibrant, and captivating to watch. Larger groups often make the fish exhibit a wider variety of behaviors and the schools enhance their well-being and reduce their stress levels.

They love open spaces to swim in but a couple of forests with tall plants will also be appreciated.

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