What Fish Can I Keep Together?
One of the most enjoyable parts of building an aquarium is choosing your fish. But just because two fish look good together doesn’t mean they should live together.
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By Michel Scavuzzo, Founder, PetCompanionAI.com
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Quick answer
The goal is to create an environment where they can live well together.
This is educational context, not a diagnosis. Read the full explanation and sources below.
A successful community aquarium isn’t about choosing the prettiest combination.
It’s about compatibility.
Before putting different fish together, I look at temperament, adult size, water requirements, swimming space and social behavior.
Start With Water Requirements
Fish sharing an aquarium need compatible water conditions.
Temperature is one of the easiest examples. Tropical fish generally require warmer water, while many cold-water species prefer cooler conditions.
You should also consider things like pH and water hardness. You don’t need to obsess over creating a mathematically perfect number for every fish, but you shouldn’t force species with dramatically different requirements to share the same environment.
Temperament Matters
Some fish are naturally peaceful. Others can be territorial, aggressive or predatory.
Even a relatively small fish can become a problem if it constantly chases, nips or stresses its tankmates.
This is especially important with fish that have long, flowing fins. Certain species are known for fin-nipping and may harass slower-moving fish.
Never assume small means peaceful.
Size Matters Too
One of the simplest rules in fishkeeping is worth remembering:
If one fish can fit another fish in its mouth, there’s a possibility it eventually will.
That doesn’t mean every larger fish will immediately eat every smaller tankmate, but predator-prey relationships should always be considered.
Research the adult size of both fish—not their size when you see them at the store.
Some Fish Need Friends
Certain species naturally live in schools or social groups.
Tetras, rasboras and Corydoras are examples of fish commonly kept with others of their own kind. Keeping a schooling species alone simply because you only want one can prevent that fish from displaying its normal social behavior.
Your stocking plan therefore needs to account for groups, not just individual fish.
Some Fish Prefer Their Own Territory
Other fish may become territorial, particularly around breeding, feeding or favorite hiding places.
Bettas are a good example of why you should research the exact situation rather than following a simple “peaceful” or “aggressive” label.
A betta can sometimes live successfully in a carefully planned community aquarium, but compatibility depends on the individual fish, tank size, tankmates and environment.
Beginner-Friendly Community Combinations
For a properly sized, fully cycled freshwater aquarium, peaceful community species can include fish such as:
- Tetras
- Rasboras
- Corydoras catfish
- Some peaceful gouramis
- Livebearers such as guppies and platies
But that doesn’t mean you should automatically put all of them together.
For example, livebearers and some popular tetras may naturally prefer somewhat different water chemistry. Individual species within these groups also vary.
Always research the exact species rather than relying only on the general family name.
Don’t Forget Where They Live in the Tank
I also like to consider which part of the aquarium each species tends to occupy.
Some fish primarily swim near the surface.
Others prefer the middle.
Bottom-dwelling species such as Corydoras spend much of their time closer to the substrate.
Choosing compatible fish that naturally use different areas can create a more balanced aquarium without unnecessarily overcrowding one swimming zone.
Introduce Fish Carefully
Even fish that should theoretically be compatible can surprise you.
After introducing new fish, watch them closely.
Look for repeated chasing, biting, hiding, damaged fins, refusal to eat or one fish preventing another from accessing food.
Compatibility charts are useful.
Your fish’s actual behavior matters more.
The Best Community Tank Isn’t the One With the Most Species
New fish parents sometimes want one of everything.
I would rather see you build a simple aquarium with a few compatible species kept in appropriate numbers than try to create an underwater collection of every fish you like.
Before adding any new species, ask:
Does it need the same water conditions?
Will it eventually become much larger?
Is it peaceful with my existing fish?
Does it need to live in a group?
Is my aquarium large enough for all of them at their adult sizes?
If those answers work together, you’re much closer to creating a healthy community.
The goal isn’t simply for your fish to survive together.
The goal is to create an environment where they can live well together.