Are Zebra Danio Aggressive?7 mins read

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Tal Halperin
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Image from Flickr

Zebra Danios are easy to take care for schooling fish but they do have a reputation for being feisty! If you have heard they make good tankmates and are suitable for beginners, but also that they can nip fins, you may be looking for more information.

This article will give you the ins and outs of their behavior without judgement so you can decide whether they are suitable for your tank. Read on to find out exactly when aggression can break out and what you can do to sort it out when it does.

Are Danios Aggressive Fish?

Danio refers to a group of small, flat-bodied, and strikingly patterned fish including the celestial pearl Danio, leopard Danio, Zebra Danio, longfin Zebra Danio, and Zebra Danio glofish. All of these are small schooling fish and differ mostly in their appearance and patterning as opposed to their behavior. They are also all relatively peaceful fish when they are kept in a sufficient group and all their other needs are met.

However, these are not shy or timid fish, and if their needs go unmet they may indeed become aggressive as a way of expressing this. Read on to find out how aggression manifests in the Zebra Danio specifically, how it interacts with the fish’s environment, and what you can do about it.

What Kind Of Danios Are There?

As outlined above, there are multiple kinds of Danios all of which have relatively similar needs. However, some of these are species you may want to keep with your Zebra Danios. Before making this decision, remember not all of them are compatible though. Apart from the common Zebra Danio, the following varieties are often found in pet shops:

1. Longfin Zebra Danio

Longfin Zebra Danio is a selectively bred species of Zebra Danio that have longer, more flowing fins. These are one of the few species you absolutely should not mix with regular Zebra Danio as the difference between them actively encourages fin nipping.

The long fins of the Longfin Danio are generally a threat and form of competition to the shorter-finned regular Zebra Danio. This is a needless cause of aggression that can be easily prevented by simply not keeping the two species together.

2. Leopard Danio

Leopard Danio
Image from flickr

There is quite a large variety of information out there about the viability of keeping leopard Danios and Zebra Danios together. In truth, it is that you can but it’s important to think of them as separate species even though the leopard Danio is technically a captive-bred variant of the zebra dino that has spots instead of stripes.

In theory, leopard Danios and Zebra Danios do join each other’s shoals. However, in practice, it’s best to ensure they have members of their own variant as fish can and do discriminate by appearance. A lone fish that is the only one of its kind is generally a target for aggressive bullying.

3. Celestial Pearl Danio

Group dynamics between the celestial pearl Danio and the Zebra Danio are similar to those between the leopard Danio and Zebra Danio. The two can coexist, but it’s best for both to have a group of their own species.

Apart from this, you may hear these fish named ‘galaxy rasbora’. However, they are not a true rasbora like the harlequin rasbora. Instead, they are also a member of the Danio family.

4. Zebra Danio Glofish

Zebra Danio glofish are not a separate subspecies but are in fact a branded variety of Zebra Danio that has been dyed with a colorful dye to make them look more visually attractive. However, beauty is in the eye of the beholder and the sad truth of these fish is that they are generally less healthy and tend to live shorter and more painful lives due to the natural die.

It’s best to steer clear of them and opt for fish that are naturally colorful instead, such as guppies or endler’s livebearers, although these do not get on with Zebra Danios as well as they do with some other species. Thus, if you are looking for colorful fish, it’s best to rethink your tank planning and considerations.

What Danio Species Get On Best With Zebra Danios?

Ultimately, the best species to get on with Zebra Danios are other Zebra Danios. They can get on with other Danios species but it’s not recommended because the species are similar enough that they will compete but different enough that they won’t swim together in a shoal.

The one species you should never mix them with is the longfin Zebra Danio due to the fin nipping issues that can arise as described in the section above.

Are Zebra Danios Aggressive When Mating?

Are zebra danios aggressive when mating?
Male fish may chase each other and nip fins as a sign of dominance especially in the presence of a female, as they may see the other fish as a competitor for the female’s attention. Image from flickr

Mating is one of the times that aggression may break out amongst Zebra Danios, but if you understand why this is, you can easily prevent it. It can be hard to sex Zebra Danios, but generally, aggression will happen between the males in order to vy for female attention. Male fish may chase each other and nip fins as a sign of dominance especially in the presence of a female, as they may see the other fish as a competitor for the female’s attention.

You can avoid this by setting up a specific breeding tank and also by ensuring a good sex ratio. If you have an equal number of females to males you won’t have issues with competition.

Are Zebra Danio Aggressive Fish Over Territory?

Zebrafish can be aggressive over territory, but it’s not as likely as it is with species like cichlids, barbs, or angelfish because they are schooling fish.

This tends to mean that all fish are in the same territory at the same time. Because the schools swim together, they are not competing over territory so they don’t see proper territorial disputes in the same way some other species do.

However, that’s not to say zebrafish are not affected by territory. In an overcrowded tank, aggression often breaks out inevitably. That’s why it’s always best to ensure your fish are in a big enough aquarium that has a variety of habitats and is enriched. It is much harder to mitigate stress in a smaller tank and correcting this takes time and money.

Are Zebrafish Aggressive Over Food?

Zebra Danios can be aggressive over food, but generally, this is less likely than aggression over mates and territory. This is because zebrafish are relatively easy to feed and they won’t necessarily use food as a way of establishing hierarchy, unlike hierarchical fish like the angelfish where dominant members of the hierarchy may outcompete subordinate members.

However, there are two main ways you can prevent aggression from breaking out over food:

  • Don’t feed only flakes! Flakes can cause gastrointestinal problems if fed alone, as fish like the Zebra Danio are omnivorous in the wild and need a fresher and more balanced diet. Flakes are very good basic food. It’s just that they shouldn’t be the only thing you feed your fish. Supplement your fish’s diet with fresh or frozen protein such as bloodworm, tubifex worm, or daphnia.
  • Feed little and often and distribute food easily. When your fish are feeding, if the food is all in one place you will cause a feeding frenzy and encourage competition. By breaking up frozen food or sprinkling flakes evenly across the surface of the water you will provide your fish with plenty of space to feed without competition.

Zebra Danio Aggression And School Size

Zebra danio aggression and school size
For most small schooling fish to feel comfortable, they need to be in a group of around six of their own kind this would protect them from predation in the wild.

You may think that Zebra Danios might hype each other up when kept in a large group. Some fish do become more hyperactive when they are kept in groups of more than 12 and you can see large schools of them swimming through a tank.

However, it is really all about getting to a sweet spot. Zebra Danio fish may well become hyperactive over group sizes of around ten or twelve but they actually tend to display the calmest behavior when kept in groups of around six or seven.

There are many reports of fishkeepers wanting an assortment of small schooling fish and opting for multiple species such as Zebra Danios minnow such as the white cloud mountain minor and neon or cardinal tetras only to find that these fish become aggressive and disputes break out when they get home.

This is because not all species are the same! And, on top of this, there can be differences in behavior between wild-caught and domestic-bred Zebra Danios, and no way of telling which is which when you purchase your fish. Thus, it is very helpful to learn about the dynamics of your individual tank by observation.

Author’s Note: For most small schooling fish to feel comfortable, they need to be in a group of around six of their own kind this would protect them from predation in the wild. Therefore, when they don’t have this sense of security that comes from safety in numbers they may act aggressively towards other fish due to fear.

What Tankmates Can I Keep Safely With Zebra Danios?

What tankmates can I keep safely with zebra danios?
Generally, the best tankmates for Zebra Danio should be nonpredatory. Image from flickr

Generally, the best tankmates for Zebra Danio should be nonpredatory. However, it can be good to keep fish with a variety of sizes and habits. For example, fish that live at the bottom of the tank like Cory Catfish won’t compete with your Zebrafish. Likewise large drifting fish like angelfish can occupy the middle of the tank while your Danios swim in a school.

What To Do About Aggressive Zebra Danio Fish?

If one of your Zebra Danio fish does become aggressive, don’t be fooled by this fish’s small size. They genuinely can cause quite a bit of damage to helpless tankmates and can even kill others of their own species. As soon as you notice aggression breaks out it’s best to monitor it and take action right away if you feel a fish is at risk of being killed. Zebrafish may show dominance by chasing and biting. The best thing to do can be to remove the offending fish.

However removing fish can affect school size and make it drop below the optimum, especially if you only started with a small group at first. Therefore if it’s possible, a better option is to transfer all the fish to a larger holding tank so they have more room.

Alternatively, to tell if the aggression is due to poor water quality, you can test for the levels of ammonia, nitrates, and nitrites, as these are most likely making your fish stressed. Once you have determined if this is the cause of aggression, you may actually find that changing the water quickly solves the problem for your Zebra Danios, and aggression levels return to normal.

1. Causes Of Aggression

Apart from dirty water, overcrowding is actually another of the leading causes of fish aggression Zebra Danio fish may look small but they are active and should be kept in a tank of a minimum of 20 gallons or 76 liters if they are to truly thrive – and that’s for a single group alone. If you are keeping them with larger tankmates, remember simply to add this amount to the ideal capacity of your larger tankmates’ tank.

2. Ways Of Managing Aggression

Aggression is generally best managed by removing the source of the aggression (cleaning the water) or separating the fish. It can be a fine balance to see which one is which and depends very much on why your fish are being aggressive in the first place.

Author’s Note: For any fishkeeper, it’s good to have a spare tank on hand. However, if you find that the source of the aggression is something else like low school size, it’s easy to simply solve it by meeting your fish’s unmet needs.

Bottom Line

Zebra Danio fish
The key to managing fish aggression and will also help you spot problems with your tank before they arise.

It is a big surprise for many novice fishkeepers how many issues can arise even with small and easy-to-care-for fish like the Zebra Danio. However, understanding this is the key to managing fish aggression and will also help you spot problems with your tank before they arise.

Author’s Note: It is best to remove the dead fish with a net, otherwise, the rest of the school may eat it. In fact, this is one of the main causes of fish suddenly disappearing. It’s generally best not to let it happen, as in the wild it tends to be a bigger predator that eats your dead fish, not the rest of the shoal. Thus it can be quite unhealthy for the rest of the school.

Frequently Asked Questions

Can Zebra Danio fish kill each other?
Unfortunately yes, it is a sad fact of aquarium-keeping that many species, including the Zebra Danio, can kill each other if they are kept in small conditions and are stressed. This isn’t pleasant and it is always a shock to find a dead fish floating in your tank. However, take it as a sign that you should investigate the source of the aggression, whether it is overcrowding, poor quality water, or your fish simply don’t have a big enough school.
Are Zebra Danio fish fin nippers?
Fin nipping is a common occurrence in aquariums and the answer to this question is that yes, Zebra Danio fish are indeed fin nippers. Fin nipping is in fact one of the most common forms of aggression overall. Zebra Danios do not nip fins from hierarchical or predatory instincts. In general, it tends to be a sign of stress or of perceived competition with the other fish. If fin nipping is occurring it’s best to check your quality and the size of your tank. This unmistakable and troublesome fish behavior is often one of the first signs that you are keeping your fish in substandard conditions.
How large a group do Zebra Danio fish need to thrive?
Generally, the optimum school size for a group of Zebra Danio fish is 6-7 this easily fits the most common 20-gallon aquariums that you can pick up in pet shops and is large enough that your fish feel secure and don’t show any issues with aggression, but small enough that they do not become overwhelmed or hyperactive. In essence, it is also the easiest school number to manage and still leaves your fish with a sufficient group if one of them dies before you can manage to replace it.
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Sydney Perry

Sydney Perry has loved fish since she was a child and has enjoyed keeping many varieties over the years, ranging from black moors and shubunkins to betta fish. As a lover of nature and of Japanese culture, her dream tank is an Iwagumi aquascape, combining fish with carefully crafted aquatic landscapes in miniature.