Whether your setting up a small fish only saltwater tank or nano-reef with corals, it’s so important to select compatible nano fish.
It used to be that if you wanted a saltwater or reef aquarium you had to set-up a large tank.
All of the equipment necessary for keeping a marine aquarium was large and too big to use on small aquariums.
Fortunately, aquarium manufacturers stepped up and designed aquariums, lighting and filtration systems perfectly matched to for keeping marine fish and invertebrates in small nano tanks.
Some aquarists consider nano aquariums to be 15 gallons or less, but others rate tanks up to 25 gallons as nano.
In this article we will not cover how to set up a small tank, as we have already done it in depth here.
We will now focus on the choice of which fish you should consider for a small tank.
So we put this guide together to help you with your fish choice for whatever small tank project you’re working on.
We have picked 16 different species which can populate a saltwater small tank. Not all of them are compatible with each other but with the due attention you can find option to match some of them in a small marine environment and avoid to lose your fish.
Why fish compatibility is important
Not all tropical marine fish are suitable for nano aquariums.
It’s common to see beautiful juvenile saltwater offered online and in fish shops.
But most juveniles will grow too large for a nano tank.
Some fish, even though they stay small, are very territorial.
This may not be a problem in a large aquarium but in a nano tank it is a disaster.
A “bully” fish will terrorize the other tank-makes and may even kill them.
If you plan on keeping corals, shrimp and other invertebrates, reef-safe fish must be selected.
Rather than talk about the fish that won’t work for nano aquariums, we’ll take a look at some of the best saltwater fish for nano tanks.
Clownfish
By Josuevg - Own work, CC BY-SA 3.0, Link
Clownfish are one of the most popular marine species.
There are many wild and captive bred clownfish available to aquarists.
Not all clownfish are compatible in a nano aquarium.
Some types are very aggressive and difficult to care for.
The clown won’t pick on corals or cleaner shrimp.
If you like clownfish and are willing to settle for a one fish aquarium, this is the clown for you.
With a larger nano aquarium you can add any of the other fish listed in this guide.
This clownfish will grow to about three inches.
Ocellaris are omnivores and should be fed meaty and herbivore foods.
Blue chromis
The blue chromis (Chromis cyaneus) is a favorite with saltwater enthusiasts.
The brilliant blue fish are beautiful and active.
In nature they’re found alone and in schools.
A group of three can be kept in a 15-gallon aquarium.
Smaller tanks should consider only one blue chromis if other fish are in the tank.
They are compatible with this nano fish list.
Mature fish can reach a length of five inches.
Feed these reef-friendly fish a combination of meaty and herbivore foods.
Royal gramma
By H. Zell - Own work, CC BY-SA 3.0, Link
The royal gramma basslet (Gramma loreto) is a peaceful reef-friendly fish from the Caribbean.
The three inch bright purple and yellow body adds color and flash to any aquarium.
Royal grammas prefer rock caves to explore, so add pieces of live rock.
Most other nano fish are compatible with basslets.
Avoid chromis and dartfish in small nano tanks.
These fish are carnivorous and require meat type frozen and prepared foods. The fish grows to length of about three inches.
Fire Dartfish
Dartfish include firefish (Nemateleotris) and dartfish (Ptereleotris) species.
Some species require a larger non nano aquarium that contains live marine plants and a rubble bottom.
These fish grow to three inches in length.
The spiked dorsal fin coupled with orange, red and white coloration makes this a striking fish.
Fire dartfish prefer a rocky aquarium with caves to hide in.
If keeping one type of fish, several firefish make an interesting display.
Dartfish are compatible with other nano fish but caution should be used if keeping a basslet or chromis in a small aquarium.
They’re carnivores and require vitamin enriched brine shrimp and mysis shrimp diet to maintain their bright coloration.
Pajama Cardinalfish
By Steven G. Johnson - Own work, CC BY-SA 3.0, Link
There are several types of cardinalfish but the Pajama (Sphaeramia nematoptera) is a favorite for small aquariums.
The yellowish face with striking red eyes contrasts with the spotted body.
The pajama cardinalfish grows to about four inches.
This fish is peaceful and compatible with invertebrates.
The three-inch fish are slow swimmers.
Blennies may become aggressive toward cardinals. Pajamas require a variety of fresh, frozen and prepared foods like shrimp, flakes, bloodworms and chopped fish.
Neon Goby
By Jmk7 - Own work, CC BY-SA 3.0, Link
The neon goby (Elactinus Oceanops) is a tiny fish that is about two inches long.
The fish enjoys darting around live rock.
The brightly colored stripes, peaceful character and hardiness make this fish an ideal candidate for a nano aquarium.
Other nano fish will live peacefully with gobies. This carnivore should be fed live brine shrimp, mysis shrimp and prepared foods.
Pink Skunk Clownfish
By Lepidlizard at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, Link
The pink skunk clownfish (Amphiprion Perideraion) is a semi aggressive clown suited for larger nano tanks.
Unlike other orange clowns, the pink skunk has a peach color with a white strip behind the eye.
Skunk clownfish grow up to four inches in length.
Captive-bred skunks are more adapted to aquarium life. An anemone makes a great partner for the skunk clown. Feed meaty foods balanced with a herbivore flake or pellet diet.
Six Line Wrasse
By Lonnie Huffman - Own work, CC BY 3.0, Link
For a nano reef, the six-line wrasse (Pseudocheilinus Hexataenia) is a perfect fit.
The attractive six horizontal blue lines makes this a favorite among saltwater fish enthusiasts.
It’s small three inch size makes it perfect for nano tanks.
The fish enjoys darting around rocky aquascapes, feeding on naturally-occurring crustaceans that live in the reef tank.
You’ll be able to combine other nano fish with a six-line wrasse.
It won’t peck corals or bully shrimp.
Another bonus is the six-line wrasse’s habit of eating bristle worms and flat worms.
Feed this carnivorous fish meaty foods, shrimp along with flake or pelleted foods.
Chalk Bass
By Emőke Dénes - kindly granted by the author, CC BY-SA 4.0, Link
This interesting Caribbean fish (Serranus Tortugarum) is a popular nano-tank species.
At three inches, the chalk bass will explore live rock and cave rock-work.
The color pattern is orange along the back with blue vertical stripes.
Chalk bass are reef compatible and get along with other nano fish.
Be aware that mature fish may start to peck at shrimp.
Chalk bass are carnivorous and require meaty foods like mysis shrimp, brine shrimp and small pellets.
Watchmen Goby
By User:Haplochromis - Self-photographed, CC BY-SA 3.0, Link
The watchmen goby (Cryptocentrus Cinctus) is a colorful four-inch fish with a yellow body with bright blue spots on the head and fins.
The watchmen goby likes to move sand a small rubble around the aquarium.
It will build a hide-out under rock-work.
Other nano fish will live peacefully with gobies.
Only mated pairs of watchmen gobies can be kept in the same aquarium.
These fish may jump out of the aquarium.
A tight-fitting lid is recommended, especially in a shallow nano-tank.
The fish can grow to four inches in length. Watchmen gobies are reef-safe carnivores.
Feed them brine shrimp, mysid shrimp and prepared carnivore foods.
Flame Hawkfish
By Brian Gratwicke - Flickr: Flame Hawkfish Neocirrhites armatus, CC BY 2.0, Link
The flame hawkfish (Neocirrhites Armatus) is a native of Fiji.
The bright red fish makes a great fish for a specimen aquarium.
Flame hawks like to sit on top of live rock ledges, watching you watch them!
They’ll feed on crustaceans that live in the rock.
That means they’ll also try to eat small aquarium shrimp.
All of these fish like to stake out a territory on rock ledges of near the bottom of the tank.
A “turf war” could break out in smaller nano aquariums.
These carnivores are easy to care for, growing to four inches.
Feed them live shrimp, marine meat foods and prepared carnivore diets.
Hector’s Goby
By Frédéric Ducarme - Own work, CC BY-SA 4.0, Link
Native to Indonesia, Hector’s goby (Koumansetta Hectori) has a dark body with vibrant horizontal yellow stripes.
This goby needs plenty of rock-work to dart in and out of.
It will graze on algae that grows on the rock.
Other nano fish will live peacefully with gobies.
However, do not add more than one Hector’s goby to an aquarium.
This omnivore should be fed a variety of foods.
Vitamin-enrichment is recommended for this goby’s diet.
Dwarf Seahorse
By Will Thomas - Image Credit
The dwarf seahorse (Hippocampus Zosterae) is difficult to care for but worth the effort.
The tiny two-inch fish are normally brown, white or yellow in color.
Some have tiny black dots.
They do not like strong water flow and are weak swimmers.
An air powered sponge filter is recommended.
Seahorses need to be able to grip vertical structures, like Caulerpa algae or plastic plants, with their tails.
Feeding seahorses involves hatching brine shrimp or purchasing live shrimp larva.
One or two fish can be kept in a five-gallon aquarium.
Small hermit crabs and snails are compatible with dwarf seahorses.
Do not add seahorses to a reef aquarium.
Black Cap Basslet
By The original uploader was Aquaimages at English Wikipedia. - Transferred from en.wikipedia to Commons., CC BY-SA 2.5, Link
The black cap basslet is a Caribbean deep water reef fish.
It prefers a rocky aquarium with caves.
The brightly colored fish has a base of bright purple with a contrasting black “cap” that runs from the heat and along the dorsal fin.
Black caps can grow up to four inches in length.
Black cap basslets will forage for live shrimp living in the rock-work.
Feed this carnivore frozen fish, shrimp and live foods.
Catalina Goby
By Stan Shebs, CC BY-SA 3.0, Link
The tiny Catalina Goby (Lythrypnus Dalli) is only two-inches in length but makes up for it with bold orange, red and blue coloration.
While the Catalina goby likes rock-work, it often perches on the rocks in plain sight.
This fish is native to the Eastern Pacific coast of the United States.
They should not be kept in warmer tropical aquariums.
This is not a difficult fish to keep but requires its own aquarium with cooler water.
Several of the same species can be kept together if the aquarium is larger than 10 gallons.
Feed Catalina gobies small meaty foods like fish, shrimp and prepared carnivore flakes.
Sharknose Goby
By LASZLO ILYES (laszlo-photo) from Cleveland, Ohio, USA - Flickr, CC BY 2.0, Link
Captive bred Sharknose Gobies (Elacatinus Evelynae) are well suited for a tropical marine nano aquarium.
Growing up to two inches, the blue and yellow fish is reef-compatible.
Only one sharknose should be kept in a nano tank.
This carnivore prefers meaty frozen and fresh foods like brine shrimp along with prepared carnivore flakes.
The sharknose goby is at home on a sandy bottom or with live rock.
Final thoughts on nano fish
Selecting fish for small nano aquariums requires careful planning.
Nano reef fish are very beautiful and interesting to watch.
Their small size makes it tempting to add too many to an aquarium, however consider that most nano fish need room to develop their own territory.
If they feel crowded, they may fight or become stressed and susceptible to disease.
In keeping a nano reef aquarium, much of the focus is on the colourful corals.
Adding one or two nano fish adds movement and interest.
If your nano aquarium is a fish only, consider adding a piece of live rock or build a cave if your fish like cover.
Before buying nano fish, research compatibility.
The general rule is to avoid keeping two of the same species in your nano tank.
No matter what type of fish you select, remember to maintain water quality and feed high quality foods.
Just because the aquarium is small does not mean it doesn’t require proper care just like a large aquarium.
We have few articles that can provide you further suggestions on this here and here.
Follow these guidelines and your nano aquarium will become a beautiful aquatic jewel, tight in your own home or office.
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