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are danios aggressive?

Are Danios Aggressive? How to Fix It.

If you have a community tank, the chances are you will already have a group of Danios in there, or are thinking about getting some. They are a very popular choice due to the fact they are crazy! There is never a dull moment when you have danios!

One of the best things about owning a community tank is having a wonderful array of different fish, covering different shapes, sizes and colours, as well as getting to see their personalities take shape as they get used to their new home.

There is a downside to having a community tank though. Sometimes trouble brews between different species, or within a species.

There is a way to eliminate this though, which is to do your research before adding a new type of fish to your tank. This way, you will spend less time stressing over the stress levels of your fish kids, and more time enjoying how they all get along peacefully together.

In this article, I’m going to discuss if danios are aggressive, what can cause any aggression, how to recognise it, and how to reduce it.

Are Danios Aggressive?

Danios are capable of showing aggression to other danios if they feel threatened, or are establishing a pecking order amongst themselves, especially if new fish have been added to the tank. They are not often aggressive to other species.

spotted danios
A pair of Spotted Danios.

Reasons Why Danios can get Aggressive.

Establishing a pecking order.

This is completely normal behaviour with danios if you have more than one male. The group needs to establish who is the boss and who isn’t. This is usually decided by very low level aggression, but at a very fast pace as that is the only way danios operate! It can get a bit more aggressive if some of the males refuse to back down though.

Not enough space.

Danios need a lot of space to swim, as well as quite a tall tank so they have plenty of space both above and below them.

Use a stocking calculator, like AQADVISOR.COM to help you work it out. They take the shape of your tank into consideration, as well as the size.

Not enough food.

A hungry fish can be a very aggressive fish. Not feeding your fish enough is as bad as overfeeding them. Getting the amount right for your tank can take a few goes to get correct, but it is very important.

They are in spawning condition.

When male danios are in spawning condition, they will have a go at other male danios if they annoy them. The male’s temperature increases when they are ready to spawn, and we all get a bit irritated when we’re too hot, don’t we? The male will basically chase his female partner constantly when they are getting ready to spawn. It can look like he is looking for a fight, but if you look closely at the other fish, you should see she has a more rounded belly than normal.

giant danio
Another pair of danios.

How do Danios Show Aggression?

There are other reasons why danios look like they are showing signs of aggression, when in fact, it is not as bad as it looks.


Sparring amongst danios is completely normal when they are in a group with more than one male. This is how they sort out their pecking order. The 2 sparring fish will basically chase each other around the tank. I know you’re probably thinking that’s what they do all day anyway, but, if you watch closely, you will see the same 2 fish chasing each other constantly. They will repeat this until they get bored (or distracted).


When danios are mating, it looks very similar to when they are being aggressive to each other.

You can tell which of your danios are males by looking at their shape. Male danios tend to be slimmer. They also have more vivid colours than the females.

glowlight danio
Glowlight Danio.

Here are a few things for you to look out for, to help you decide if your Danios are actually being aggressive, which could threaten the health or well-being of your other fish.

Signs of aggression to look out for.

  • Their fins spread, or stand up rigid, rather than flowing in a relaxed manner.
  • Enhanced colouring.
  • Darker eyes.
  • Twitching head.
  • Skittish behaviour (extremely hard to tell when danios are skittish all the time anyway!)

How to Reduce Aggression in Danios.

Correct male to female ratio.

I would always recommend having your male to female ratio as 1 male to every 3 females. This will stop the females from being harassed constantly by the males.

If you want to breed your danios, then you need to keep 2 males to 1 female.

Correct tank size.

This is essential no matter what types of fish you have. One of the main reasons why fish get stressed is because they don’t have enough space. This can result in fish hiding away, or fighting with their own type, or other breeds, because they feel trapped.

Always make sure you don’t overstock your tank. When calculating how many fish can fit into your tank, you have to calculate using their adult size, not the size they currently are. Always try and understock slightly to be on the safe side.

As well as considering the size of your tank, you also need to think about the shape of it as well. This is essential when it comes to fish like Danios, who are one of the most active fish to put in your tank. They need plenty of space to dart around in.

Have hiding places.

Having some ornaments and plants in your tank is always a good idea. You don’t have to have real plants either, the imitation ones do their job in providing shelter or hiding places for fish for when they need to just have a moment to themselves.

Fish can feel exposed when in a stressful situation so it is good to have somewhere for them to retreat to. Having a hiding place or a bit of shelter makes the fish feel a lot safer.

Just always make sure that you don’t fill your tank up with things so much that your fish have no room to swim and have fun, as that can be just as stressful as having nowhere to hide.

Keep the correct number of Danios.

Danios are shoaling fish so need to be kept in a group of at least 6. They thrive and are happiest in groups of around that number. Don’t have too many more in your tank (unless your tank is massive) because that can lead to aggression over hierarchy.

zebra danio
Somebody didn’t get the memo about numbers..

Feed them the correct amount.

When you are new to fishkeeping, you are always told that you should never overfeed your fish. It is just as important that you don’t underfeed them as well, as that can also have a damaging effect in your tank.

Hungry fish can be aggressive fish as they may have to race to get to the food first if you aren’t feeding them enough.

It really is a case of trial and error at first when it comes to feeding your fish the correct amount.

A rule of thumb is that all the food you feed your fish should be eaten within 3 minutes. If your fish finish eating everything well within that time, you are not feeding them enough. If, after three minutes, there is still a lot of food floating around the tank, you are feeding them too much, so remember to adjust what you give them the next time you feed them.

Get your timing right.

It is best to add your danios to the tank at the same time, and preferably when they are juvenile.

If you were to add danios to a tank that already has some in it, this would cause a problem. The fish in the tank will already have sorted out their pecking order and will be more than a bit miffed at new guys being added.

Best Tank Mates for Danios.

Never put any danios into your tank if you have large, predatory fish in as they will turn your danios into lunch.

Danios are renowned fin nippers, so don’t mix your danios with any slow moving fish with long fins, eg, angelfish.

Angelfish are known to be fin nippers as well (ironic, I know), but this is mostly when they are squabbling with other angelfish.

A popular choice of tankmate for danios are tetras. They tend to just hang out in their own little group, but are just as active, so won’t be freaked out by the danios playful behaviour. Other danios and mollies etc are also fine as tankmates.

zebra danios
Loving or hating?


Danios can make a great addition to a community tank, provided you don’t overstock your tank by adding too many fish in.

Male danios do show aggression to other danios, but this is normal behaviour and nothing to worry about.

Related Articles:

Why does my danio stay at the bottom of the tank?

Do danios change colour?

Can danios jump?

How many danios can I put in a tank?

Will danios eat all of my plants?

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