Which fish can live together? Aquarium compatibility guide

Which fish can live together in a freshwater aquarium? The answer doesn't just depend on the fish's temperament. To have a successful community aquarium, you must also take into account the temperature, pH, water hardness, available volume, adult size, and the behavior of each species.

Two fish might seem peaceful and yet be incompatible simply because they don't require the same water conditions. Conversely, several species can perfectly share an aquarium when their needs are consistent.

In this guide, discover how to check the compatibility of aquarium fish, which pairings can work, and which mistakes to avoid.

How to tell if two fish are compatible?

Before introducing multiple species into the same aquarium, check at least these six elements:

• maintenance temperature;
• water pH and hardness;
• adult size;
• behavior and territoriality;
• swimming zone;
• need to live alone, in pairs, or in groups.

Good compatibility is therefore based as much on water chemistry as it is on fish behavior.

Quick freshwater fish compatibility chart

1. Check water parameters

Two species living in the same temperature range are not necessarily compatible. Water hardness and pH also matter.

For example, Guppies and Platies generally enjoy fairly mineralized water, whereas many South American Tetras prefer softer water.

Maintaining all these species at an intermediate value just to mix them is not always the best solution.

It is better to build your population around the natural parameters of your water.

2. Compare fish behavior

Some species are very calm while others are territorial, nervous, or very active.

A peaceful fish can be constantly stressed by a much more lively species, even without actual attacks.

Cichlids, for example, can strongly defend a territory during breeding. Their compatibility therefore depends heavily on the volume and layout of the tank.

3. Consider adult size

A common mistake is to choose a fish based on its size at the time of purchase.

Some individuals sold at a few centimeters long can become much larger as adults.

In general: if a small fish can fit into another's mouth, it can become prey.

4. Respect schooling fish

Neons, Rasboras, Tetras, Corydoras, and many other species are gregarious.

Keeping only two or three individuals of a species that naturally lives in a group can cause stress and abnormal behavior.

Before adding several different species, it is often better to build a proper group of a single species.

5. Distribute different swimming zones

In a community aquarium, it can be interesting to pair fish that use different zones:

• surface and upper section;
• middle section;
• bottom of the aquarium.

This distribution allows for smarter use of the available space.

However, this does not mean you absolutely must have a fish in every zone. The volume and species' needs remain the priority.

Example of an aquarium with mineral-rich water

When water is relatively hard and suitable for livebearers, you could consider:

• Guppies;
• Platies;
• certain species adapted to the same parameters.

However, you must anticipate their high breeding capacity. A correctly sized aquarium can quickly become overcrowded if births are not controlled.

Example of a peaceful Asian aquarium

In a planted aquarium with suitable water, an Asian population can be built around:

• Rasboras for the middle zone;
• Kuhli loaches for the bottom;
• possibly a calm territorial species chosen with caution depending on the volume.

The advantage of an aquarium built around the same geographical origin is that it is often simpler to find species with similar needs.

Example of a South American aquarium

In suitable soft water, several South American species can also be paired:

• Tetras or other small schooling characins;
• Corydoras adapted to the tank's parameters;
• Otocinclus in a sufficiently mature aquarium;
• possibly a pair or group of dwarf cichlids in an appropriate volume.

Dwarf cichlids like some Apistogramma can become much more territorial during breeding periods. You must therefore provide enough space and hiding spots.

Can you mix Guppies and Neon Tetras?

It's possible in some aquariums, but it's not necessarily the most consistent pairing.

Guppies generally enjoy more mineralized water than the Neon Tetra. The fact that they can survive in the same aquarium does not necessarily mean that their maintenance conditions are optimal.

When starting out, it is often better to select species that have truly similar water needs.

Can you put a Betta with other fish?

This depends heavily on the Betta's temperament, the size of the aquarium, and the other species.

Some cohabitations work while others quickly become problematic.

Fish with large, colorful fins, particularly some Guppies, can be particularly problematic with a male Betta splendens.

A species-only aquarium remains the simplest solution for a Betta.

Can you put a goldfish with tropical fish?

This pairing is generally not recommended.

Goldfish have different needs than the majority of tropical fish, notably regarding temperature, volume, and maintenance.

They should therefore be considered a population of their own rather than fish intended to complement a tropical aquarium.

Territorial fish: watch out for cichlids

The term "cichlid" includes a huge number of very different species. Some are relatively peaceful while others strongly defend their territory.

It is therefore impossible to consider all cichlids as compatible or incompatible with a single rule.

For these fish, always check:

• adult size;
• necessary floor area;
• behavior during breeding periods;
• number of potential territories in the aquarium;
• species already present.

Watch out for fish presented as "cleaners"

A Corydoras, Ancistrus, or Otocinclus should never be added solely to clean the aquarium.

These fish have their own dietary needs and must be maintained like any other species.

A properly maintained aquarium does not rely on fish tasked with eating waste or algae in place of the aquarist.

How many species can you put in an aquarium?

There is no universal number.

An aquarium comprising two or three species correctly maintained in suitable groups will often be more balanced than an aquarium containing many species with only a few individuals of each.

The volume, dimensions of the tank, behavior, and biological load are more important than the simple number of species.

Tips for a successful community aquarium

• Choose fish according to your water parameters.
• Check their adult size before purchasing.
• Respect the minimum group sizes for gregarious species.
• Avoid overloading the aquarium with different species.
• Add plants, driftwood, and hiding spots when species need them.
• Introduce the population gradually.
• Carefully observe behavior after each introduction.

What about fish with shrimp?

Compatibility between fish and shrimp requires additional precautions. A peaceful species can still consume juvenile shrimp.

We have dedicated a complete guide to this subject: which fish to put or not put with aquarium shrimp?

New to the hobby?

If you are primarily looking for accessible species for your first aquarium, also consult our guide dedicated to freshwater fish suitable for beginners.

Discover 10 freshwater fish for beginners →

Frequently asked questions about fish compatibility

Which fish can live together in an aquarium?

Compatible fish are those that share similar needs in temperature, pH, hardness, and volume, while having compatible behaviors. You must therefore choose a complete population rather than checking fish two by two.

Can you put Guppies and Corydoras together?

It is possible if the parameters match the needs of the specific species of Corydoras chosen. "Corydoras" encompasses many species whose requirements are not all identical.

Can you put Guppies and Platies together?

Yes, they generally have relatively similar needs. However, you must anticipate their rapid breeding and have a sufficient volume.

Can you mix fish from different regions of the world?

Yes. An aquarium does not necessarily need to be a strict geographical biotope. The essential thing is that the selected species have compatible needs.

Are peaceful fish necessarily compatible?

No. Two peaceful species may require totally different temperatures or water hardness. Behavior is therefore only one of the compatibility criteria.

What to do if two fish are fighting?

First, identify the cause: lack of space, insufficient territory, wrong ratio, group too small, or real incompatibility. If the attacks present a risk of injury, it may be necessary to separate the fish.

In summary: how to choose compatible fish?

• ✅ choose species adapted to the same water parameters;
• ✅ check their adult size;
• ✅ respect their social needs;
• ✅ adapt the population to the volume and dimensions of the tank;
• ⚠️ beware of highly territorial fish;
• ⚠️ do not mix species just because they are described as "peaceful";
• ❌ never buy a fish just to "clean" the aquarium.

Final word

The compatibility of fish in a freshwater aquarium is not just about whether two species will fight. A good population must share consistent needs in terms of water, temperature, space, and behavior.

By building your aquarium around a few truly compatible species rather than multiplying different fish, you will generally get a more stable, natural, and enjoyable tank to observe.

Just starting out? Also check out our article on the 10 errors to avoid in aquariology .