How To Choose Fish for Your Saltwater Aquarium

Working on setting up a saltwater aquarium? Great choice! A colorful marine aquarium is educational, aesthetically pleasing, and even promotes relaxation. But… what fish should you put in it? You can’t just combine the species from your local aquarium store willy-nilly: many will fight or even eat each other.

Let’s get you off to a good start. Below, learn how to choose fish (and corals, and invertebrates) for your aquarium.

How to choose fish: Centerpiece

One of the most important things we’ve learned during our years of building custom aquariums for our clients and giving fishkeeping advice is that stocking an aquarium is a thing you should plan. Yes, it’s more fun to go to the pet store and point at random fish, but your experiment may end in tears if you go about things in this way.

Unfortunately, you can’t always rely on the aquarium store staff’s advice either. Some stores are fantastic, while others can be… less than consistent. No matter which category yours falls in, doing your own research can save you—not to mention your wallet, as saltwater creatures are expensive—some heartbreak.

Our top tip for beginners? Pick a fish or invertebrate you’re interested in (and that’s realistic for your set-up) and stock the tank around that. This way your centerpiece can shine while everyone around it gets along.

Here are some questions you should ask before putting any fish, including the centerpiece, in your tank:

• How much space does this fish need as an adult? The little wiggly things you see at your local aquarium store are almost always babies. Some can grow to monstrous adult sizes! “I’ll upgrade later” is an easy thought, but the execution is often a different story.

• Does this fish match my experience level? Saltwater species in particular can be very finicky about factors like diet and water quality. If a fish or invertebrate is listed as Medium or Hard and you’re a beginner, maybe it’s best not to waste your money.

• Am I willing to do the work required to keep this fish alive? It may match your experience level, but can you be bothered? Some fish may need something like five small feedings every single day, or come with a host species that’s difficult to keep alive.

• Does this fish eat corals? If you (want to) grow corals, this is an important question. Fish range from “reef safe” to “tentatively reef safe” (keep with cheap or fast-growing corals only) to “voracious coral hunter”. The latter two require a FOWLR (Fish Only With Live Rock) set-up.

These questions obviously also apply to invertebrates. As a rule of thumb, most saltwater shrimp are unproblematic, while saltwater crabs can be big troublemakers. Most snails don’t cause issues, nor will feather duster worms; clams and starfish are prone to dying prematurely.

Tip: If you’re a big reef enthusiast, it may even make more sense for you to start by picking your favorite coral(s), rather than a fish or invertebrate. Do you want a tank full of easy softies like Xenia, somewhat more challenging LPS like Zoas, or finicky but beautiful SPS such as Acropora? Most of the questions you should ask beforehand will stay the same.

How to choose fish: Tankmates

Once you’ve established the centerpiece you’ll be working around, it’s time to figure out who it can live with. Of course, all the initial questions—does it fit in my tank? Does the lay-out match it? Can I even keep it alive?—apply to every additional species you add. But now, you also need to ensure each candidate matches your eye-catcher.

To start, research the centerpiece using resources like FantaSEA’s fish and invertebrate care guides or Tropical Fish Hobbyist’s online articles. Then, use the information you find to fill out this table we came up with to narrow down your options.

Meet the Tankmate Table:

You can discard any categories that get a cross and further inspect any that get a tick. Look for species within the approved categories that match your centerpiece in terms of activity level (not too hyper or shy), habitat (likes similar environments), and size (bigger fish will almost always eat smaller fish if they get the chance).

Yes, there’s a lot of research involved! We think that’s worth it: not only will your aquarium hopefully be a more harmonious place, but you’ll also learn plenty of things that will benefit you later in your fishkeeping journey.

To wrap things up, let’s have a look at a few examples. As we’ve described, we’ll start from a single centerpiece species and work around that.

How to use the tankmate table

I want to keep a mandarin goby

When you research diet and habitat for the mesmerizing mandarin goby (which is not actually a goby at all, but a dragonet), you’ll find out the former is the big bottleneck for this species. It needs a very mature tank, as it basically only eats copepods. Its tankmates need to be mellow and leave it alone, or it won’t be able to find food.

You can keep a mandarin goby in an aquarium of at least 50 gallons.

Conclusion: Based on the table, you may set up a mandarinfish tank with mixed corals, a pair of ocellaris clownfish, and a ground crew of watchman gobies and pistol shrimp. Other small, polite tankmates (especially those from the nano section) will also work.

I want to keep a dwarf lionfish

Because normal lionfish are darn cool, but who has a 120-gallon aquarium lying around (except for us here at FantaSEA, of course)? You can keep a dwarf lionfish in a 50-gallon, though you should keep in mind its temperament—predatory but easily disturbed.

Here’s how you’d pick its tankmates:

Conclusion: you can combine your dwarf lionfish with species that can’t fit into its mouth and won’t bother it: assessor basslets, Salarias blennies, adult percula clownfish, dwarf angelfish and the like work just fine. And don’t forget the corals!

I want to keep SPS corals

If you’ve got some experience growing soft and LPS corals and things have gone well for you so far, maybe you want to challenge yourself with more finicky SPS (Small Polyp Stony) species like Montipora or Acropora. These count as centerpiece because they require you to build the tank around their needs.

Here’s what your table would look like:

For a tank focused on SPS corals, reef-safe small fish and invertebrates will work fine. Gobies, blennies, gramma, small wrasses, clowns, small shrimp, feather dusters, snails, and many more should work fine. If you want to keep multiple SPS corals, it’s helpful to place them at least 5″ apart. Coral warfare is a real thing.

I want a mantis shrimp

How cool is the colorful and intimidating mantis shrimp? Good news if you like these funky inverts: the smaller species can thrive fine in a 10-gallon, while a 20-gallon aquarium allows you to keep the rather intimidating larger species.

What about their table? Here it is:

Conclusion: Haha, got you! If your table looks like this, you’ll have to set up a single-species aquarium—or at least your options will be extremely limited. Mantis shrimp are vicious predators, though at least you’ll be able to keep yours with some nice corals.

Conclusion

Stocking your first aquarium is an adventure! It involves a lot of research and careful thinking about which fish will get along and thrive in the type of tank you’re looking to set up. We promise it’s all worth it when you’re done—and also that you’ll get better at it over time.

If you’re thinking this whole stocking business is too much work, we can’t blame you. But we can help: we’ve been doing this for a long time and have gotten pretty good at it. Contact FantaSEA Aquariums with your ideas and we can design, set up, and indeed stock your saltwater fish tank for you. We get our hands wet so you don’t have to!