20 Small Saltwater Aquarium Fish for a Spectacular NANO Tank

small saltwater fish header
There was this one time when space constraint became the reason I opted out of a large marine fish tank and instead went for a tiny one. That said, finding a small yet peaceful saltwater fish to keep in my nano aquarium was not at all easy.

I managed to find fish species famous for being among the smallest ones in the trade, but they were not really suitable for beginners to the hobby.

In fact, it was even more of a challenge to uncover ones that were also nano reef-safe and yet remained under 3 inches of body length.

Here’s a teaser, a fish that grows no more than 2.5 inches (I’ll uncover its name further down in the article):

By luisgo

Luckily for you, I’ve already spent hours researching what nano saltwater fish would be best for a small tank. I found quite a few cool entries, so you may want to bookmark this article for further references.

20 Small Saltwater Aquarium Fish for an Impressive Nano Tank

During my research for small fish, I stuck to the commonly accepted rule that a nano aquarium may be any tank that has a volume capacity of between 5 and 30 US gallons of water.

For this reason, I made sure to keep the record of nano fish that remain under 3.5 inches of full body length.

To stock a nano aquarium you can try these 20 small saltwater fish:

1. Gumdrop Coral Croucher – Caracanthus madagascariensis

A Gumdrop Croucher hiding behind a coral

By chopsie

Maximum Adult size: 2 inches (5 cm)
Suggested tank size: 15 gallons
Predominant Personality: Peaceful and somewhat withdrawn. Not a typical display fish.
Suggested Companions: Clown Gobies, Trimma Gobies, Coral Crouchers in 30-gallon tanks, Eviota, larger non-aggressive fish are also suitable.

At 2 inches of full-grown body length, the Gumdrop Coral Croucher is small enough saltwater fish to squeeze through crevices, aided by its even tinier pectoral fins. These nano fish are more at home in a 15 to 30-gallon reef aquarium with adequate amounts of live rock and branching Small Polyp Stony corals (SPS).

The Gumdrop Croucher prefers to withdraw to the lonely sections of the tank like the crevices or caves.

It may be out of sight for days, not hiding from anyone but rather enjoying time alone.

Therefore, you may need to target-feed it since it will not easily avail itself at mealtimes. That’s where a feeding tool such as a syringe or tweezers comes in handy.

Anyway, in my observations, the Gumdrop Coral Croucher fish is one of the most peaceful inhabitants any seasoned hobbyist could wish for in a saltwater aquarium.

However, in rare cases, it can harass males from its own kind, so it is best to keep a single male or a pair if the tank size allows it.

This saltwater fish species may be small, but it belongs to the Scorpaeniformes.

Therefore, as a relative to the scorpionfish, it has venom in its short spines.

Fortunately, the toxin is purely a defense mechanism used only as a last resort and under extreme provocation.

So just handle it with care, which is to say do not over-squeeze the fish.

I am yet to hear a report of other aquarium fish getting hurt by a Gumdrop Coral Croucher, as they will usually stay away from it.

Feed your Gumdrop Coral Croucher fish on Mysis and brine shrimp or other frozen foods.

A fish tank of 10 to 15 gallons is appropriate as a minimum living space for these small marine fish, but a 30-gallon one is better.

I recommend this aquarium equipment for a Gumdrop Coral Croucher:

2. Flaming Prawn Goby Fish – Discordipinna griessingeri

A Flaming Prawn Goby laying on the substrate

By EllisJuan

Maximum Adult size: 1 inch or 2.54 cm.
Suggested tank size: At least 5 gallons.
Predominant Personality: Peaceful and less shy with time.
Suggested Companions: Non-aggressive gobies, shrimp, and other flaming prawn gobies.

The Flaming Prawn Goby is a cool saltwater fish that is also small and docile enough for a pico reef tank. It is, therefore, possibly one of the best and most colorful fish species you could get for your 5-gallon aquarium.

The Flaming Prawn Goby reaches a maximum adult size of 1 inch (2.54 cm), which makes it one of the very few saltwater fish suitable for a small 5-gallon nano tank.

It likes hiding (more so among live rocks or on a sandy substrate), perhaps fearing that its small size makes it easy prey.

Though the Flaming Prawn Goby is reef-safe, putting it in a relatively large aquarium with reef corals may be a sure way to never really see it again.

A friend of mine did just that, and he would only catch a glimpse of this small saltwater fish every couple of months.

For this reason, I recommend keeping the Flaming Prawn Goby in a small fish tank. This way you may be able to enjoy its stunning beauty more often.

The way this marine fish looks is absolutely impressive, with its pointed dorsal fins and the red patterns on its tail fins standing out.

Bear in mind that this nano fish jumps out at times, so keep the aquarium under a lid.

Though among the smallest, The Flaming Prawn Goby is rather pricey due to high demand versus low supply.

So if you are like me and have a taste for rare gems, go for this unique fish.

This goby enjoys feeding on small brine shrimp, zooplankton such as copepods, and other meaty micro foods. It will usually scavenge the sand bed for its food.

I recommend this aquarium equipment for keeping a Flaming Prawn Goby:

3. Tailspot Blenny – Ecsenius stigmatura

Closup photo of a Tailspot Blenny

By Rickard Zerpe

Maximum Adult size: 2.5 inches or 6.3 cm
Suggested tank size: At least 10 gallons.
Predominant Personality: Will likely avoid conflict and mind its own business.
Suggested Companions: Yellow tangs, gobies and other non-aggressive community reef fish.

The Tailspot Blenny grows to a maximum size of 2.5 inches or 6.3 centimeters, from head to tail. In my experience, this rather small fish is peaceful and easy to care for, which makes it an excellent choice for a beginner. A 10-gallon aquarium will provide sufficient space for this fish.

I’ve also found another advantage of keeping one: if you want an algae-eating marine fish for your nano tank, give the Tailspot Blenny a try. This fish especially enjoys eating the algae on the live rock.

Essentially Tailspot Blennies are as good as Lawnmower Blennies at taking care of hair algae problems in a reef tank but are not as aggressive.

This, in combination with their small size of 2.5 inches makes them an excellent algae eater for a nano tank with reef corals.

I should also point out that the Tailspot Blenny along with most other Blennies and Gobies in general, are more resistant to parasites such as saltwater Ich because these fish have a thick slime coat.

Though there are tested treatments for saltwater Ich that work, it can be a lot of hard work to eradicate.

The marine Ich is even more difficult to get rid of with a treatment that’s reef-safe, so a Tailspot Blenny can save you a lot of headaches in the long run.

Anyway, I would recommend that the aquarium of your Tailspot Blenny has plenty of live rocks for them to perch on or hide in if need be.

They prefer the tank’s bottom and the crevices as their hangout spots.

The Tailspot Blenny is another peaceful fish that will not harass the other tank-mates in your saltwater aquarium.

House it with other equally friendly nano fish.

For a Tailspot Blenny I would recommend the following aquarium setup:

  • As with most other nano tanks, I would recommend to set up a Neo-Therm heater, which can be adjusted to match the temperature required for a thriving Tailspot Blenny
  • Make sure you have enough live rock for the Tailspot Blenny to hide in

4. Captive-Bred Orchid Dottyback Fish – Pseudochromis fridmani

An Orchid Dottyback Fish in front of a rock

By Darth__Nader

Maximum Adult size: 3 inches (7.62 centimeters)
Suggested tank size: Between 25 and 30 gallons for a single specimen.
Predominant Personality: Semi-aggressive with captive-bred ones being more peaceful.
Suggested Companions: Large angel tangs when in larger tanks, smaller clown fish, banggai cardinals, large damsel and hawkfish, most gobies.

The Orchid Dottyback is a reef-safe fish species that grows to a maximum of 3 inches (roughly 7.6 cm). This purple nano fish is one of the best options to add extra color to your small saltwater reef aquarium.

I would say that its beauty is further enhanced by the two black lines that run from the nose tip up through the eyes.

Note that the fish is active and so a single specimen is most comfortable in a 25 to 30-gallon tank as a minimum.

According to my research Orchid Dottybacks may need to be captive-bred in order to be more tame and manageable in terms of temperament.

The captive-bred ones will likely be shyer, especially when acclimating.

Thus, provide these small saltwater fish with enough hiding places such as established coral reefs or a good amount of live rock in your aquarium.

However, I would not go as far as saying that they are entirely docile; the Orchid Dottyback is semi-peaceful and may, at times, chase the smaller fish in the tank.

Moreover, it becomes territorial should it anticipate intrusion, especially from its own kind. If you keep two, they will fight over their perceived territory until one ends up killed.

If you really want to keep more than one Orchid Dottyback in the same aquarium, you may add them in the tank at the same time so that they learn to tolerate each other.

From what I found, it seems likely that more live rocks also helps to alleviate aggression.

The Orchid Dottybacks will eat Krill shrimp, bristle worms, and other frozen aquarium foods for carnivores.

5. Pygmy Coral Croucher – Caracanthus unipinna

A small Pygmy Coral Croucher in a tank.

By Wolfgang Suchy

Maximum Adult size: 1.5 inches or 3.8 cm
Suggested tank size: 10 gallons.
Predominant Personality: A loner who’s confident and not scared of larger tank mates.
Suggested Companions: Equally peaceful fish, like the Chromis varieties, but can basically be housed with anything that is not super aggressive and the size of the tank mates does not seem to matter.

Measuring a paltry 1.5 inches (3.8 cm), the Pygmy Coral Croucher is a small reef fish that suits a saltwater nano tank with lots of SPS corals. A 10-gallon reef tank with enough live rock will make an adequate home for a single specimen.

This species loves to spend its time perching among the branching corals.

From my observations, the Pygmy Coral Croucher rarely comes out in the open.

For this reason, in a coral reef aquarium, this little fish may get out of sight for, sometimes, days.

It is peaceful and shy but I would not recommend it for a beginner because it may need special care like target-feeding.

Also, I would handle them with caution because they have venom glands in their dorsal fins, though they rarely employ the weapon.

Upon some further research, I found that the sting from a Croucher rarely feels stronger than a bee’s sting.

Remember that keeping this fish in a nano aquarium is actually recommended if you want to see it from time to time.

6. Banggai Cardinalfish – Pterapogon kauderni

Three Banggai Cardinalfish roaming around in an aquarium.

By mell_bell

Maximum Adult size: 2.7 inches (around 7 cm), but rarely a specimen may reach 3 inches or 7.6 cm.
Suggested tank size: At least 30 gallons.
Predominant Personality: Semi-aggressive, if the fish feels there’s not enough space to retreat to. In a good environment, they will remain calm and docile.
Suggested Companions: Clownfish, Blennies, Butterflyfish, Boxfish, Firefish, Gobies.

An adult Banggai Cardinalfish grows to a maximum of 2.7 inches or slightly less than 7 centimeters. An aquarium of 30 gallons is ideal for these small saltwater fish because they love to swim and therefore a rather spacious nano tank comes in handy.

The Banggai Cardinalfish is a cool-looking fish with black spots and a forked caudal fin.

From my experience, they hide from predators or other imaginary threats and therefore require rock caves and crevices to hide in.

The temperament of this fish is, in my opinion, controversial at the least. I would classify the ones I’ve kept as rather peaceful because they enjoyed living and interacting with other members of the aquarium.

However, during my research, I’ve found that occasionally the Banggai Cardinalfish may turn aggressive against its own species when it comes to claiming or marking territories.

What I found works best in such scenarios is having more caves in the aquarium.

Other than that this nano aquarium fish is perfectly reef-safe and their main day-to-day activity seems to be calmly patrolling the middle water column.

What’s important to remember is that you should feed the fish on meaty foods such as bloodworms but not dry or prepared foods like flakes or pellets.

7. Gold Assessor Basslet Fish – Assessor flavissimus

Close up photo of a Gold Assessor Basslet Fish

By DT Prime

Maximum Adult size: 3 inches or 7.6 cm.
Suggested tank size: At least 30 gallons for a single specimen.
Predominant Personality: Semi-aggressive towards its kind but very peaceful towards other tank mates. Needs a well-thought nano tank with a lot of hiding places to feel comfortable, so it may not be suitable for beginner aquarists.
Suggested Companions: Anything but big, aggressive fish.

The Gold Assessor Basslet measures almost 3 inches when fully grown. Therefore this saltwater fish may be kept in a small tank of 30-gallons.

This predominantly yellow fish feels most at home in a reef aquarium with corals and rock landscape.

My experience has been that Gold Assessor Basslets have a rather timid temperament and hence it takes them days or weeks to get used to their new fish tank.

If you keep more than one Goldfish Assessor Basslet, expect fights over territories, especially if the aquarium has fewer rocks or corals.

However, they won’t harass other tank-mates or even invertebrates.

I would recommend that you only get one specimen per nano reef tank as 2 specimens would need more than 30 gallons to get along.

This small fish is big on price these days, as it is somewhat hard to come by. However, I believe that it is nevertheless a wonderful addition to any saltwater aquarium.

8. Panamic Barnacle Blenny Fish – Acanthemblemaria hancocki

A Panamic Barnacle Blenny Fish swimming over the sandbed.

By Cinder1977

Maximum Adult size: 1.8 inches or around 4.5 cm.
Suggested tank size: 5 to 10 gallons, preferably the latter.
Predominant Personality: Docile, until they start dashing around when it’s feeding time. VERY entertaining overall.
Suggested Companions: Clown Goby, Dartfish And Cardinal Fish, Seahorses in pico reefs, Clown fish, Chromis.

The Panamic Barnacle Blenny Fish measures 1.8 inches or around 4.5 centimeters and is green or white with red spots, while its dorsal fins, lips, and iris are red. This super colorful fish is peaceful all-year-round and is a perfect addition to a small saltwater aquarium.

I find these predatory fish to be lively, super-fast, and entertaining to watch as they dash at lightning speed to grab food at mealtimes, after surveying the area.

Once a Panamic Barnacle Blenny has the food, it usually hurries back as fast.

One thing they never do is sit back at meal times while the rest eat. But it is best you ensure they get their fair share of food (read target or spot feeding) if the competition is too much for them.

In fact, I’ve found target feeding to be key for successfully keeping these small fish.

I recommend feeding your Barnacle Blenny multiple times a day if possible.

I would say that they are otherwise easy to take care of, and if you’re a beginner who’s not afraid of a little more work you will likely pull it off.

This micro fish enjoys finely-chopped meaty foods such as frozen brine or Mysis shrimp.

In my experience, a 10-gallon reef aquarium would be fine with these cool fish, provided it has plenty of rocks with crevices to act as potential hideouts.

Panamic Barnacle Blennies are one of my favorite nano saltwater fish for a single species aquarium. Things could get really entertaining when it’s feeding time.

9. Twin Spot Goby – Signigobius biocellatus

Two Twin Spot Goby Fish next to each other.

By Rickard Zerpe

Maximum Adult size: 3.5 inches or 8.9 cm.
Suggested tank size: At least 10 gallons.
Predominant Personality: Peaceful and timid bottom dwellers that may fight their own kind for territories.
Suggested Companions: Better kept in a species only if it’s a nano tank but – Sharknose, Tailspot Blenny, Yellow Watchman Goby, Green Clown Goby, peaceful nano Gobies in general, NO aggressive feeders

The Twin Spot Goby A.K.A. The Two Spot Goby is another stunning nano fish that can suit a reasonably small saltwater aquarium. It grows to a maximum of 3.5 inches in length (nearly 9 cm).

This fish species is white all over with splashes of orange markings and has an overall remarkable appearance in the aquarium.

The fish is a bottom-feeder and will always be seen scooping sand while sifting through the sandy substrate.

However, they are not easy to feed because they will generally refuse the food you offer.

Since the sand itself may not have the right diet for them, they can end up skinny.

To avert such a scenario, you need to squirt some live or frozen, vitamin-enriched foods into the sand.

Their menu can consist of Mysis shrimp, microworms, etc.

Just make sure the food is extra small and the currents slower so that the Twin Spot Goby can eat comfortably.

Needless to say, the Twin Spot Goby needs intensive care, especially in the acclimation period.

Microfauna in aged sand is the best food source for the Twin Spot Goby. Ideally, you’d have these fish in a mature aquarium with a sandbed rich on self-sustainable microfauna. Therefore, the Twin Spot Goby is not a saltwater fish I’d recommend to a beginner looking to stock a nano tank.

While they are exciting to watch as a pair, they can only live peacefully together if they were simultaneously introduced into the tank to bond from the start.

If a second Two Spot Goby is added later, the fish would likely fight over territory.

These small Goby fish are, however, generally peaceful as they never bother with other tank-mates.

A 10-gallon fish tank will likely be enough, as long as it has a sandy substrate with a large enough population of micro worms.

10. Court Jester Goby – Koumansetta rainfordi

A close-up snapshot of a Court Jester Goby swimming in a saltwater aquarium.

By JDowns

Maximum Adult size: 2.8 inches or 7.1 cm.
Suggested tank size: 10 gallons, preferably established.
Predominant Personality: Super peaceful.
Suggested Companions: Equally peaceful tank-mates.

Also known as Rainford’s Goby, the Court Jester Goby fish measures a maximum of 2.8 inches or 7.1 centimeters in its adulthood. With its small body size and calm temperament, the Court Jester Goby becomes a great addition to a nano saltwater tank.

As with most non-aggressive micro gobies, it may be best if the aquarium has a decent amount of live rocks and sand on which this small fish can spend time grazing.

The Court Jester Goby is an algae-eating nano fish and likes the lower levels of a marine reef tank.

The rocks should have hiding places too because in my experience the fish can be really timid and shy.

The CS Goby is usually really peaceful yet active as long there are no aggressive tank-mates around.

You may often spot it somewhere alone nibbling on softer hair algae or sifting through the sand.

Some users report this fish doing better in reef tanks with finer sand beds.

What’s important to remember about the Court Jester Goby is that you will rarely see it eat.

With a well-established microfauna in the sandbed, however, it will take care of its own.

These fish are technically omnivores and you should not get one just for the sake of eating algae in the reef aquarium.

Court Jester Gobies are somewhat finicky eaters and I would never recommend getting one to someone who’s just starting out with saltwater fish keeping.

I have seen these fish eat frozen or live Mysis and brine shrimp, so keep that in mind if you think yours is getting skinnier.

Nonetheless, this nano fish species is super colorful and has its own interesting personality.

A 10-gallon reef tank can be enough for this cool fish.

Get one only if you like a challenge and are after a small saltwater fish that loves to eat from time to time.

11. Longspine Cardinalfish – Zoramia leptacantha

A school of Longspine Cardinalfish

By eksblenny

Maximum Adult size: 2.5 inches or 6.3 cm.
Suggested tank size: 20 gallons for a small school of 3, but you can keep a large school in big reef tanks.
Predominant Personality: May be aggressive towards one another until they establish a pecking order, but after that, they will calm down and do their thing.
Suggested Companions: Peaceful dartfish, firefish, clownfish, wrasses, gobies, and so on.

Measuring about 2.5 inches as an adult, the Longspine Cardinalfish is one of the schooling fish that you can keep in a small saltwater aquarium. In fact, you can keep them in both small and large tanks as long as there are no aggressive tank mates to bother them.

While each Longspine Cardinalfish does not have much color to it, they make an impressive lot when in a group.

In my observations, they are relatively slow, and rather methodical swimmers.

The bare tank size for 1 specimen is 10 US gallons, but you can put 3 or 4 in a 40 gallon one, as the bioload of these saltwater fish is relatively small.

There may be some aggression among their own at fist in order to establish a pecking order.

When you keep them in a sizable group in larger reef aquariums, Longspine Cardinalfish soon form a hierarchy which is strictly observed as they shoal together.

In my experience, they are also non-aggressive and will likely avoid conflicts with other tank-mates in the system.

However, they are predatory fish and may prey on smaller micro fish in your saltwater tank, so do keep this in mind if you want to keep other nano fish in the same tank.

The general rule is that the other fish should not fit in the Cardinalfish’s mouth.

Longspine Cardinalfish get timid if they are fewer in numbers and will retreat behind live rock, or coral reefs if they feel insecure.

They also will feed reluctantly and prefer not to swim in the open during the daytime unless you keep them in a large school.

A tank of 20 gallons is enough if you are keeping 2-3 of them.

12. Flametail Blenny Fish – Enchelyurus flavipe

A Flametail Blenny Fish near a coral.

By S├ębastien Stradal

Maximum Adult size: 3.5 inches (8.9 cm).
Suggested tank size: 30 gallons.
Predominant Personality: Depends on the individual, can be both calm or somewhat aggressive to other similarly-shaped nano reef fish.
Suggested Companions: Be cautious with other small blennies, and gobies, but larger reef fish with peaceful temperaments are suitable.

The Flametail Blenny is a beautifully colored fish that grows up to a maximum of 3.5 inches and is also reef-compatible. Its size, colors, and reef-compatibility makes it an excellent addition to a nano tank with a water capacity of 30 gallons.

During my research on these blennies, I’ve found that they love to eat and never let a morsel go to waste.

They would mainly hang out at the aquarium’s bottom near the rocks, seeking food from one crevice to the other.

The Flametail Blenny is an omnivore but will enjoy feeding on algae, so get it if you need a small saltwater fish that can eat the algae regularly.

Provide live rocks with microalgae to keep them busy.

Supplement their algae diet with Mysis or brine shrimp.

Flametail Blennies are neither peaceful nor aggressive and the temperament of yours totally depends on its personality.

Most of them will keep their cool and do nothing but scavenge for food when they get comfortable in their new tank.

On occasion, however, they may turn aggressive against dartfish or gobies over territories if the fish tank is too small.

For that reason, I would say that a 30-gallon community aquarium is suitable for these small and lively saltwater fish.

Note that the Flametail Blenny fish is a high-jumper so you should likely have the lid on your reef tank tight.

13. Mini Dart Goby Fish – Aioliops megastigma

Five Mini Dart Goby Fish schooling together.

By Tierra y Mar

Maximum Adult size: 1 inch or around 2.5 cm.
Suggested tank size: 5 to 10 gallons for a couple of specimens.
Predominant Personality: Active swimmers that won’t bother anyone else in their aquarium.
Suggested Companions: Just avoid the more aggressive marine fish.

The maximum grown-up size of a Mini Dart Goby fish is just about 1 inch, which makes them an appealing choice for a small tank.

They are cute and enjoy sticking together because they really love one another, meaning they don’t fight among themselves. These small, and cool-looking fish will peacefully shoal in the midsection of your saltwater reef aquarium, troubling no tank-mates.

A fish tank of 5 to 10 gallons will be comfortable for a small school of 3-5 specimens as their bioload is relatively unnoticeable in a closed system.

Before you rush to find these in some online shop or your LFS, I should point out that though they seem to perfectly fit a peaceful nano aquarium, they are not really beginner-friendly.

They may become very picky about their foods and on top of that, not many things fit their small mouths.

Mini Dart Gobies need to be fed multiple times a day and the most success I’ve had was with baby brine shrimp and live copepods.

Another thing I should point out about these micro fish is that their life span is relatively short – 1.5 years with extremely diligent care.

For that reason, I consider the Mini Dart Goby to be a nano reef fish that requires expert-level care.

14. Firefish Goby – Nemateleotris magnifica

Photo of a beautiful Firefish Goby in a reef tank.

By TurboMP

Maximum Adult size: 3 inches (7.6 cm).
Suggested tank size: 20 gallons/pair.
Predominant Personality: Peaceful towards others, but can get aggressive among each other.
Suggested Companions: More passive clownfish, Shrimp Gobies, Possum wrasses, Watchman gobies, peaceful cardinalfish, reclusive anthias, non-paired pajama cardinalfish, tailspot blennies.

This yellowish-headed, flame-colored fish measures 3 inches when fully-grown and is rather timid.

The reef aquarium, the Firefish Goby is kept in, may need to have handy hideouts into which the fish can quickly bolt when startled.

Therefore create rocky caves for it, or else it would jump out of the tank when scared or stressed if there’s an open lid.

However, like some other fish from this genus, this slender saltwater fish is not afraid to confront and fight family members, though this may only happen if they are crowded in a very small tank.

Otherwise, even with this shortcoming, the Firefish Goby is still, in my opinion, one of the most peaceful pet fish a saltwater fish keeper can keep in a nano reef tank. It will never bother or get in the way of other tank mates.

They love to swim in the middle section of the aquarium’s water column, once they judge the coast is clear.

Bear in mind that this fish enjoys low water currents, so be mindful when choosing your reef powerheads.

The minimum fish tank capacity to successfully keep a pair of Firefish Gobies is 20 gallons.

15. Royal Gramma Fish – Gramma loreto

Royal Gramma Fish up close

By OceanicTemple

Maximum Adult size: 3.5 inches or almost 9 centimeters.
Suggested tank size: 30 gallons with lots of caves and crevices.
Predominant Personality: May become aggressive towards fish with similar appearance but is overall easy-going.
Suggested Companions: Gobies, various Jawfish, Boxfish, Clownfish, Hawkfish, Firefish, Angelfish, rabbitfish.

The Royal Gramma Fish is a reef-compatible nano fish that grows to up to 3 inches long, on average. You can safely keep a single Royal Gramma specimen in a small reef aquarium of 30 gallons, as long as there are no fish that resemble its body shape.

This small fish can get aggressive if its living space is occupied by fish who look similar, such as some blennies.

The Royal Gramma may end up relentlessly chasing the perceived competitor unless the saltwater aquarium provides sufficient chilling spots for both (caves, crevices, dense reef corals).

In my experience, the best approach to keeping a small Royal Gramma without incidents is to add last to the nano reef tank.

This way it will feel too new, which will reduce the “I own everything” behavior.

Once a Royal Gramma establishes a territory, a conqueror may first have to kill it to get the place.

Though I think the Royal Gramma is one of the coolest saltwater fish that remain small, I recommend exercising caution when planning a reef tank with them in mind.

Anyway, at times the Royal Gramma fish swim upside down, to look at life from a different perspective, as they navigate about the aquarium.

This behavior shouldn’t alarm you when it’s done close to a cave or other surface.

However, if the fish does it out in the open it may be a sign of swim bladder issues.

The Royal Gramma is a hardy, reef-safe fish which means that it’s fairly easy to care for one.

Therefore The Royal Gramma is suitable for a beginner who’s setting up his or her first saltwater nano aquarium.

Of course, these small fish can be kept by beginners as long as the aquarist has done prior research on their behavior.

Feed your Royal Gramma fish on (preferably) Mysis and brine shrimp but know they are not a picky eater.

16. Ocellaris Clownfish – Amphiprion ocellaris

An Ocellaris Clownfish in front of a rock.

By JisuanjiHou

Maximum Adult size: 3.5 inches or 8.9 centimeters.
Suggested tank size: 20 gallons.
Predominant Personality: Semi-peaceful.
Suggested Companions: Other Damselfish, Tangs when in large aquariums, Dartfish, Angelfish, Blennies, Anemones, Gold assessor fish, cardinalfish, chromis.

An adult Ocellaris Clownfish may reach a maximum of 3 inches or nearly 8 centimeters in body length. Because of its size, this fish may be a good fit for a small nano tank, but caution should be exercised with its cohabitants, as the Ocellaris Clownfish can be semi-aggressive.

Apart from their bright coloration, the fish is famous for seeking refuge in the clusters of stinging anemones.

However, my experience with them has been that you can keep one even without an anemone.

I’ve found that they are hardy, acclimate quickly, and are relatively easy to take care of.

The Ocellaris Clownfish readily eat many types of marine food and are safe for a reef aquarium system.

However, Clownfish are still a type of Damselfish, which are known for their aggressive behavior.

If you’re a beginner to saltwater tanks but want an Ocellaris as a centerpiece nano fish for yours I’d advise you to add the specimen last to the aquarium.

This way the fish won’t give new additions a bad time.

It’s also worth noting that the Ocellaris Clownfish is overall calm upon proper care and a balanced aquarium environment.

Peace can have its limit, however, so do not mix different clown species together if you want to maintain order.

I would not add more than one or a pair, as this would be more than enough if I wanted to avoid incidents with the other nano fish.

I should note that the Ocellaris is not the smallest clownfish:

The smallest Clownfish breed is the Percula clown, reaching no more than 2.6 inches in total body length. However, the Percula clownfish are considerably more aggressive than an Ocellaris and are not as hardy.

This is my main reason for excluding them from this list.

Anyway, a 20-gallon reef tank is an excellent home for a pair or a single specimen of Ocellaris Clownfish.

17. Sharknose Goby – Gobiosoma evelynae

A small Sharknose Goby surrounded by corals.

By Laszlo Ilyes

Maximum Adult size: 1.8 inches or 4.6 cm.
Suggested tank size: 10 gallons as a bare minimum, preferably 15.
Predominant Personality: Super peaceful and full of personality. A really active fish.
Suggested Companions: Clownfish, Wrasses, Powder Brown, and other tangs in larger tanks, blennies, gobies, Comets, and generally any peaceful to semi-aggressive saltwater fish.

A mature specimen of Sharknose Goby grows to about 1.8 inches. Such a size makes this reef fish small enough to be a reasonable candidate for a nano saltwater tank. Sharknose Gobies are extremely peaceful and would often clean other tank mates from parasites, a valuable role in a community aquarium.

I find watching these small fish thrilling as they are full of personality and the whole community starts acting uniquely around them.

The Sharknose Goby quickly becomes popular among its tank mates for ridding them of dead scales, and external parasites.

I’ve witnessed other fish literally lining up in front of the Sharknose’s cave to get cleaned.

The goby comes out, cleans its larger fish, and goes back, no questions asked.

It’s an interesting phenomenon you’d definitely like to watch.

I’ve found that you may add a Sharknose Goby to your reef tank purely as a parasite control agent.

In fact, if you stick your hand in the water, the fish will clean it too.

This striped fish is obviously peaceful and won’t chase or hurt other small fish.

I would recommend the Sharknose Goby to any nano reef enthusiast.

The only negative to this fish is its rather short lifespan of 1.5 years.

Anyway, supplement their parasite menu with frozen brine shrimp and live worms.

A saltwater fish tank of at least 15 gallons is accommodative enough for the Sharknose Goby.

18. Yellow-Striped Cardinalfish – Apogon cyanosoma

A Yellow-Striped Cardinalfish swimming in a reef aquarium.

By Bernard DUPONT

Maximum Adult size: 2.5 inches or 6.4 cm.
Suggested tank size: at least 10 gallons.
Predominant Personality: Really serene.
Suggested Companions: Flasher Wrasse, Dartfish, Gobies, Blennies, and any other non-aggressive marine fish.

The Yellow-Striped Cardinalfish is a slender, large-eyed fish that measures no more than 2.5 inches when mature.

There are 6 yellow stripes along the body of this saltwater nano fish.

The color pattern, along with a fake eye close to their tails, helps in maneuvering the predators at night.

The coloration makes it hard to tell which direction the fish moves next, especially when they’re in a group.

These slow swimmers create a strict hierarchy at first but it’s a common misconception that they will form schools.

The Yellow-Striped Cardinalfish rarely shoal; they do it when squeezed in a fish tank that’s too small.

No family squabbles whatsoever so you can keep a small group in your nano reef aquarium.

Nevertheless, you can keep a single specimen in a 10-gallon tank without issues.

These small beauties are also peaceful, hardy, and easy to keep. I would definitely recommend them to a beginner who’s just starting out with small saltwater fish in a nano reef aquarium.

Feed the yellow-striped Cardinalfish frozen shrimp or bloodworm, though they’re not a picky eater and will likely eat any pellets as well.

19. Clown Goby Fish – Gobiodon okinawae

A bright Yellow Clown Goby Fish over a coral.

By bonedude420

Maximum Adult size: 1.5 inches or 3.8 centimetres.
Suggested tank size: 10 gallons.
Predominant Personality: Peaceful but will pick on SPS corals and according to some reports even LPS would not be safe.
Suggested Companions: Tangs in larger tanks, other Gobies, Ocellaris Clownfish, Comet fish, Cardinalfish, most Blennies, Assessors, and Anthias.

The Clown Goby measures a mere 1.5 inches at most but still stands out in an aquarium due to its vibrant, uniform color, which is either yellow or green.

I especially like the cool-looking, Yellow Clown Goby.

Anyway, this well-built, sturdy fish enjoys perching on coral branching or live rocks or just swimming in the open where you can admire its attractive color.

A mated pair will live peacefully in a nano aquarium. The fish is generally friendly to other tank-mates but is generally not reef-safe.

Though they do feel more at home in a reef fish tank a Clown Goby will most likely pick on colonies of stony corals with small polyps (SPS).

For this reason, I would not attempt to keep these nano fish if I wanted a small reef tank with SPS corals.

Anyway, you could still keep them in a simple saltwater tank with live rock and a sandbed.

The Clown Gobies need caves and crevices to cool off when stressed or exhausted.

Due to their small size, a 10-gallon nano tank is suitable for a couple of these small saltwater fish.

20. Falco Hawkfish – Cirrhitichthys falco

A Falco Hawkfish perching over a coral in a reef tank.

By Murrel

Maximum Adult size: 2.5 inches or 6.4 centimetres.
Suggested tank size: 30 gallons to give other smaller fish room to hide.
Predominant Personality: Relatively aggressive towards smaller fish and invertebrates, but won’t brother fish of the same size.
Suggested Companions: Same-size or larger but peaceful tank-mates.

A fully-grown Falco Hawkfish will measure roughly 2.5 inches in total body length. This saltwater nano fish is hardy and makes a fantastic candidate for a small tank with reef corals.

This cool saltwater fish is absolutely full of personality.

It perches on rocks or corals, quietly watching and noting everything going on in and out of the aquarium.

The Falco Hawkfish is a keen observer, always the first one to see you approaching with food and the first to avail itself for it.

I won’t say the Falco Hawkfish is outright aggressive as some aquarists put it, but it may exhibit its predatory behavior by preying on smaller fish and invertebrates.

Because of this, I do not recommend housing it with the smallest of tank-mates.

During my research on this fish species, I’ve found that no invertebrates should be added after the Falco Hawkish because it will mistake them for food.

In fact, add shrimp prior to the Falco or with the lights off. Either way, the Falco won’t be able to spot them easily.

Other tank mates should be at least 1.5 inches to not be treated as a potential meal.

Feed your small predatory Falco Hawkfish on marine meat, Mysis, and brine shrimp.

I find it fascinating to watch this nano fish grab a piece like a hawk, fly with it to some secluded spot and devour it before returning for another.

An aquarium with a volume capacity of 30 gallons and a lot of hiding places is necessary for a Falco Hawkfish to feel comfortable.

Nano Fish Doesn’t Always Mean Peaceful Fish

handfeeding two small clownfish
One should not assume that all nano fish are simply too small to be aggressive or a threat to other tank-mates.

When it comes to (mis)behavior, size matters in the least.

An otherwise peaceful fish’s temperament can be influenced by external factors like the species of its aquarium companions.

On the other hand, I’ve found that most dwarf Damselfish, for example, are usually described as peaceful but will actually drift towards aggressive behavior.

A good example of such nano fish is the Green Chromis.

This is not always the case, but I have personally observed enough horror stories involving these fish.

In fact, it’s why I did not include Chromis in the list above, notwithstanding its popularity.

It’s a good fish but from what I’ve experienced, it can be annoying to keep with peaceful tank-mates.

The bottom line is: choose nano fish carefully and be absolutely sure the aquarium settings favor all of the tank’s inhabitants.

What Nano Pet Fish Should You Get For A Small Tank If You Are A Beginner?

a beautiful small reef tank with corals and fish

Christopher Marks

For beginners with small saltwater tanks I recommend looking into the Tailspot Blenny, the Royal Gramma Fish, a single Ocellaris Clownfish, a Sharknose Goby, Yellow-Striped Cardinalfish, and Clown Goby Fish.

All of these fish are small, generally hardy, and less demanding, which makes them easy to look after.

Nevertheless, do some research on whether the fish you chose is tropical and get your nano reef tank a small heater if needed.

The listed species will acclimate relatively quickly and eat a variety of foods, so any diet mistake by a beginner may not have adverse repercussions.

A quick tip to beginners from my experience: get a beneficial bacteria supplement to cycle your nano fish tank faster.

Leave me a comment in the Comment Section below with the species of fish you’re considering for your new aquarium.

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