How To Choose Fish for Your Freshwater Aquarium

Setting up your first—or tenth—freshwater aquarium? Figuring out which fish you’ll keep in it is always one of the most important steps. But which of the dozens of available species do you like? Which will get along? And which match in terms of water parameters? Is your head spinning yet? Probably.

Don’t worry: during our years of keeping fish and stocking tanks for clients, we’ve come up with a pretty fool-proof, 6-question system that will help you establish which fish are a match. Let’s have a look at how to choose fish for your freshwater aquarium!

“Community” fish

If you’re just starting out with your first tank, the variety of fish even in a small aquarium store can be overwhelming. All those colors and patterns! Folks tend to start off their fishkeeping adventures trying to stuff as many of these gems as possible into their tanks. Sounds great until the inevitable crash happens, or their aquatic pets start turning on each other.

Although we view them as relatively basic creatures, fish≠fish. They’re all different. Although pet stores will label anything a “community” fish, the many species available are different in more ways than you might think:

• Diet: Most fish are omnivorous, but some have a serious taste for… fish. Obviously, these can’t always be combined with peaceful or tiny schooling species.

• Position in the water column: You’ve got your bottom dwellers (recognized by their downturned mouths), your mid-level schooling fish, and your top dwellers (upturned mouths for catching insects that have fallen in the water). Too many in the same water layer can be a problem.

• Temperament: There’s no way around it—some fish are bad neighbors. They’re territorial, like to nip at long fins, or disturb their tankmates in some other manner. Others are mellow and inoffensive, or even lean towards being shy and easily stressed.

Pick your favorite

So how do you avoid falling into the trap of haphazardly combining pretty fish that may or may not end up getting along with each other? Our advice is to pick your favorite and build your aquarium, including its inhabitants, around it. The best aquariums are those set up with a purpose!

Once you’ve chosen your centerpiece fish, you can ask a series of questions about each potential tankmate to figure out if it’s a good fit:

• Does this fish match my experience level? Some fish are more finicky than others. For beginners, anything listed as easy is in; intermediate fish can be considered, while those listed as hard are best avoided lest your first community tank end in heartbreak.

• Will this fish outgrow my tank as an adult? Remember that most are sold as babies and will grow significantly larger than they are now. Aquarium store advice on aquarium size is unfortunately not always trustworthy, so do your own research.

• Does the lay-out of my tank match this fish? For example, hillstream loaches make for inoffensive tankmates, but need a specialized ultra-high flow to thrive. Probably not the right pick!

• Will this fish get along with the centerpiece I’ve chosen? What about the other tankmates I’ve selected so far? A tranquil gourami won’t like living with hyperactive guppies. The guppies, on the other hand, can suffer if you combine them with a species that likes nipping their long, flowy fins.

• Do the water parameters in my tank match this fish? If you’ve made your tank’s water quite hard and basic to please those guppies, then the gourami wouldn’t have worked anyway: it likes things soft and acidic.

• Which water layer does this fish live in? If you’ve already got two species in the middle water layer, then it may be best to pick a top or bottom dweller next to avoid territorial squabbles and a messy, disjointed look.

Obviously, answering these questions will require a bit of research. A lot of people have said a lot of things about which fish get along, and not all the sources out there are equally reliable.

We’ve got almost 70 fish care guides for you here at FantaSEA Aquariums, all based on scientific research and years of experience, so be sure to check those out (use the search bar!). If your fish choice isn’t in there, Seriously Fish is another great source of info for freshwater species—it’s highly accurate and has profiles (including compatibility information) for more fish than we could name.

Tip: We keep saying fish here, but you can of course also replace that with “invertebrate”. The exact same rules apply if you want to build your new aquarium around, say, dwarf crayfish (though for full-sized crayfish, we’ll have to refer you to the section below on the single-species set-up, because the answer to question #3 will always be no for them—big crays hunt and kill fish).

Example

Just to clarify things, let’s run a little example, shall we? Let’s assume you’ve fallen in love with the funky glass catfish—not unusual for folks who have just discovered these odd, see-through fish at their local aquarium store.

If you haven’t bought your fish tank yet, great. You now know it needs to be at least 30 gallons (preferably long), which is what works best for these catfish. You also know that you’re going to want the water to be soft and acidic, interspersed with plants, rocks, and driftwood, to help imitate the slow-flowing waters they inhabit in their native Southeast Asia.

Now, you can start narrowing the choices in your local aquarium store down to the ones that are suitable for living with glass catfish. As an example, let’s ask the questions we posited above for five common fish: rummynose tetras, bristlenose catfish, swordtails, dwarf gouramis, and tiger barbs.

We’ll use the care guides linked to here as sources, though again, you can look them up on Seriously Fish as well. All five potential tankmates are listed as easy to intermediate, so that won’t be a limiting factor. Great!

1. Will this fish outgrow my tank as an adult?

Remember: the fish you find for sale in your local aquarium store are usually babies. Bristlenose catfish, for example, may be pinky-sized when you buy them but reach 5″ in length!

• Rummynose tetra minimum tank size: 20 gallons ✅
• Bristlenose catfish minimum tank size: 30 gallons, though its bioload is high and something larger would be ideal ❓
• Swordtail minimum tank size: 30 gallons ✅
• Tiger barb minimum tank size: 20 gallons ✅
• Dwarf gourami minimum tank size: 30 gallons ✅

➡️ Everyone’s still in the running, though the catfish gets a mark on its record.

2. Does the lay-out of my tank match this fish?

Your glass catfish will want a long tank rather than a tall one, as they’re around 3″ in length with long barbels and this need some swimming room. As we’ve seen, they like a planted tank with a relatively low flow level.

Does that match our potential tankmates?

• Rummynose tetra: from seasonally flooded, small blackwater rivers ✅
• Bristlenose catfish: mostly Amazon rivers and floodplains. Likes similar décor, but needs some flow ❓
• Swordtail: very varied habitats in Mesoamerica, so it’s highly adaptable ✅
• Tiger barb: smaller tributaries in Southeast Asia ✅
• Dwarf gourami: densely planted swamps and ditches in Southeast Asia ✅

➡️ Things aren’t looking great for the bristle catfish, but no dealbreakers yet.

3. Does this fish get along with the centerpiece I’ve chosen?

Glass catfish are somewhat shy. They don’t like boisterous tankmates, especially those who may be interested in nipping at their long antennae.

• Rummynose tetra: gets along with everyone ✅
• Bristlenose catfish: very unlikely to bother its tankmates, especially because it’s a bottom dweller ✅
• Swordtail: friendly but very wiggly and active. May nip long fins and antennae. ❓
• Tiger barb: boisterous and notorious nippers. ❌
• Dwarf gourami: also somewhat shy, only bothers its own species. ✅

➡️ The barbs would drive your glass catfish nuts, while the swordtails are a maybe.

4. Do the water parameters in my tank match this fish?

• Rummynose tetra: soft and acidic ✅
• Bristlenose catfish: soft and acidic ✅
• Swordtail: hard and alkaline. You’re out! ❌
• Dwarf gourami: soft and acidic. ✅

➡️ Swordtails are very adaptable, but they didn’t evolve to live in soft and acidic waters. Best save them for a different type of set-up.

5. Which water layer does this fish live in?

• Rummynose tetra: middle layer, same as your catfish, but should work if you don’t add any more mid-layer fish ✅
• Bristlenose catfish: bottom layer, great choice ✅
• Dwarf gourami: top layer, great choice ✅

➡️ No problems here.

Verdict

There you have it! The tiger barbs are out on account of their guaranteed nippiness, while the swordtails are excluded because their ideal water parameters don’t match glass catfish—and anyway, they can potentially be nippers as well, and are quite boisterous.

The bristlenose catfish scored two question marks, based on which we’ll also exclude it. It’s better suited to riverine set-ups with high water turnover and oxygenation than the tranquil stream tank we’re going for, after all.

But hey, now you know you’ve got an open space for another bottom dweller. You can find some more options in that category, like the kuhli loach and the Corydoras catfish, and re-run the questions. You’ll find that both score a perfect 5/5 green ticks, so that sorts the lower water layer.

You’re now left with something like the following: a solid peaceful community for a calm, planted 30-gallon long tank. All the water layers are filled, there will be minimal or no aggression, and all the fish share similar preferences. You’re set up for success!

• Glass catfish x6
• Rummynose tetra x10
• Dwarf gourami x1
• Kuhli loach x6
• Optional: a few snails or shrimp

The single-species set-up

What if the fish you chose to build your aquarium around doesn’t get along with anyone? When we mention the SSSU (single-species set-up) to beginning aquarists, they sometimes look at us like we’re crazy. Why would you buy an entire aquarium for a single fish? Sounds like a waste. And yet, as they gain experience, most fishkeeping enthusiasts eventually set up one or multiple of these tanks.

Some fish just aren’t suitable for the community life. They’re too aggressive (or too shy), too particular, or just don’t show their best colors and most interesting behavior when they’re surrounded by a bunch of tankmates. But don’t rule them out just yet!

As I write this, I’m planning a tank for shell dwellers of the genus Neolamprologus. These African cichlids can be kept with other fish, especially if it’s just one or two peaceful top dwellers that don’t mind very hard and alkaline water. Still, most aquarists like to keep them alone because they’re incredibly territorial for their size.

Reserving an entire tank just for a harem of shell dwellers is worth it because they allow us the opportunity to perfectly fine-tune our tank to their needs. We’ll go for a sandy substrate, plenty of rockwork, a few plants, and most importantly: lots and lots of empty shells. The end result is a harmonious, peaceful aquarium that allows us to observe all of the shellies’ fascinating natural behaviors.

A few other examples of freshwater species that need an (almost) SSSU include freshwater puffers, goldfish, and Betta fish—plus, as mentioned earlier, all non-dwarf crayfish. Folks who like to breed certain species, like Apistogramma, will also usually keep them alone so they can focus on reproducing.

Conclusion

When choosing fish for your new community aquarium, don’t scramble to fit as many species as possible into the tank. Instead, pick a species you actually like or are fascinated by, and build your tank around it. We promise you’ll enjoy it more!

As you can see, there’s a lot more to stocking an aquarium than just pointing at the fish you like at the pet store. If you don’t have the time to carefully play fish matchmaker, contact FantaSEA Aquariums; we’ll design, build, and indeed, stock your tank for you, so all you have to do is enjoy it.