20 Best Fish for a 20 Gallon Tank

Posted by on 12/22/2023

If you own a 20-gallon tank, you have plenty of stocking options to choose from. Tanks of this size can weigh a whopping 165 lbs when full, and hobbyists will want to carefully plan out their tank layouts. 

If you're deciding what to choose for your 20-gallon aquarium, we're going to recommend 20 excellent stocking options, so that you can build a well-rounded tank.

20 Best Fish

Hobbyists upgrading from a 10-gallon aquarium will have many additional stocking options in a 20-gallon setup. Plecos, Rams, and Dwarf Cichlids are just a few of many new species you can explore in a 20-gallon tank.

Best of all, 20-gallon tanks are easier to maintain than their nano-sized counterparts. Due to the tank's larger size, water chemistry changes are less sudden, and hobbyists will have more wiggle room to address water chemistry issues before they evolve into a bigger problem.

Here are 20 fish to help get you started.

German Blue Ram

The minimum tank size for these fish is 20 gallons, making them a unique option for hobbyists looking to stock their 20-gallon tanks. German Blue Rams are cichlids, and they display similar aggressive behavior.

Hobbyists will appreciate the bold personalities of these fish, but they may want to consider other species if their 20-gallon tanks are already stocked with peaceful community fish, otherwise, you'll be asking for a territorial dispute.

Image of a German Blue Ram
Kraipitch Supyuenyong/Shutterstock.com
A German Blue Ram Cichlid

Balloon Ram

Balloon Rams are a controversial fish. Their balloon-like appearance is a result of hybridization - breeders continuously crossbreed the fish to develop more pronounced features. While some consider their appearance to be quite unusual, others place a lot of value on their unique appearance. We'll leave it up to you to decide whether or not the Balloon Ram is the right fish for you.

A Blue Balloon Ram
Joan Carles Juarez/Shutterstock.com
A Blue Balloon Ram

Queen Arabesque Pleco

Plecos are a joy to own, and without a doubt one of the most beautiful is the Queen Arabesque. Hobbyists will appreciate the fish's small size and zebra-like colors, but those looking to acquire the fish will need to have a tank with plenty of available driftwood. Similar to other plecos, the Queen Arabesque will rasp on available wood in the tank - an essential part of their overall diet.

Queen Arabesque Pleco
chonlasub woravichan/Shutterstock.com
A Queen Arabesuqe Pleco

Green Phantom Pleco

The Green Phantom is a stunning pleco, with a lemon-lime colored body, adorned with small, yellow dots. Just like other plecos, the Green Phantom will require plenty of driftwood to rasp on.

Hobbyists should be aware that there are two Green Phantom Plecos, both share the same L classification number, L-200 Hemiancistrus subviridis and L-200 Baryancistrus demantoides. We cover the differences in more detail in our care guide, Green Phantom Pleco: Care, Size, Appearance & More.

Green Phantom Pleco
5snake5/Wikimedia Commons
A Green Phantom Pleco


While keeping an angelfish in a 20-gallon tank is possible, they're best suited for larger tanks. However, if you have a 20-gallon tank that is tall instead of wide, it is possible to keep one or two of these fish. Keep in mind that when fully grown, angels can get up to 12 inches in length.

If you decide to acquire some angelfish for your 20-gallon tank, we advise having a backup plan in place in case you need to upgrade to a larger-sized tank.

A Freshwater Angelfish
You Touch Pix of EuToch/Shutterstock.com
A Freshwater Angelfish

Green Kubotai Rasboras

20 gallons is plenty of space for a group of Green Kubotai Rasboras, and hobbyists should have no problem keeping up to 20 of them in a tank this size.

Seeing a large group of these fish move above a dark-colored substrate, or in front of a large group of red background plants is a sight to behold!

Green Kubotai Rasbora
Rays Aquatics/Light Fish
A Green Kubotai Rasbora

Blue Emperor Tetra

We're big fans of the Blue Emperor Tetra. While these fish can be quite hard to acquire, hobbyists will appreciate the fish's blue coloration and active personality. In a 20-gallon tank, aquarists should have no issues keeping up to 15 of them at once.

Blue Emperor Tetra
Pavaphon Supanantananont/Shutterstock.com
A Blue Emperor Tetra

Apistogramma Cacatuoides

If you own a 20-gallon tank, you'll be able to care for dwarf cichlids. One of the most common is the Cockatoo Dwarf Cichlid (Apistogramma cacatuoides). Male apistos are known for their brightly colored fins, which display a vibrant orange and black coloration.

An Apistogramma Cacatuoides
Daylowdart/Light Fish
An Apistogramma Cacatuoides

Platinum Blue Medaka Ricefish

While white-colored ricefish tend to be a bit more common, the rare Platinum Blue color variant makes an excellent choice for a 20-gallon tank. Due to their small size, hobbyists can keep up to 12 of these fish in a 20-gallon tank. 

Ricefish are also capable of living in cold-water conditions, a unique feature that allows the hobbyist to experiment with different types of aquascapes.

A Platinum Blue Ricefish
Pavaphon Supanantananont/Shutterstock.com
A Platinum Blue Ricefish

Neon Tetra

The Neon Tetra is an aquarium staple. Native to the Amazon, these fish are always in high demand. Their bright blue bodies and red stripe that extends into the fish's tail fin make them an attractive option for hobbyists looking to add a pop of color to their tanks.

Hobbyists can stock 15 of these fish in their 20-gallon tanks.

A Neon Tetra
A Neon Tetra

Green Neon Tetra

Slightly smaller than the Neon Tetra is the Green Neon Tetra. We tend to think the fish has a stronger blue coloration than it does green, but we'll leave it up to you to decide.

Due to the fish's small size, hobbyists can keep up to 20 of them in a 20-gallon tank, just be sure to stay on top of your regular maintenance routine to keep your aquarium water in tip-top shape.

A Green Neon Tetra
Pavaphon Supanantananont/Shutterstock.com
A Green Neon Tetra

Spotted Blue Eye Rainbowfish

Hailing from Papua New Guinea and first described in 1911, the Spotted Blue Eye is a beautiful fish that only reaches about an inch in length, making it a great choice for a 20-gallon. 

Hobbyists can keep a small shoal of about 8-10 of these fish in their 20-gallon tanks.

A Spotted Blue Eye Rainbowfish
Der Regenbogenfisch/Wikimedia Commons
A Spotted Blue Eye Rainbowfish

Rocket Clown Killifish

Often difficult to acquire, the Rocket Clown Killifish is a brightly-colored fish known for its rocket-like tail. These fish tend to hang near the water's surface, hunting for their next food source that they can consume with their upturned mouths.

Hobbyists can keep up to 15 of them in a 20-gallon tank, however, you'll need a tight-fitting lid, as these fish are known to jump out of their tanks.

A Rocket Clown Killifish
A Rocket Clown Killifish

Kribensis Cichlid

These omnivorous cichlids are a favorite among hobbyists for a reason. Their hardiness makes them an excellent choice for hobbyists new to cichlid-keeping. 

With a life expectancy of about 5 years, hobbyists can keep 2 of them in a 20-gallon tank. Be aware, that these fish tend to be a bit on the aggressive side, but not nearly as aggressive as other cichlids, such as the Electric Blue Jack Dempsey, or Cuban Cichlid.

Kribensis Cichlid
danifox88/Light Fish
A Kribensis Cichlid

Apistogramma Agassizii

Native to the Amazon, Apistogramma agassizii is a small, territorial fish that uses its brightly colored fins for courting females. The species is quite resilient, and many hobbyists have cross-bred the fish to produce a variety of different color strains, such as the Agassizi Fire Red.

Hobbyists can keep a single Apisto Agassizii in a 20-gallon tank. 

Apistogramma Agassizii Fire Red
DesertDiscus/Light Fish
An Apistogramma Agassizii Fire Red

Golden Dwarf Cichlid

Next up on our list is the Golden Dwarf Cichlid. Known as one of the most peaceful dwarf cichlids on our list, hobbyists can keep a pair of these fish in their 20-gallon tanks.

These fish breed quite regularly in captivity, so hobbyists looking to get their hands on a male/female pair should have little issues when it comes to spawning. However, some may view their propensity to breed as a detriment in keeping the species.

A Golden Dwarf Cichlid
A Golden Dwarf Cichlid

Ember Tetra

Ember Tetras are some of the smallest fish on our list, but their small size might be their biggest advantage in a 20-gallon tank. Hobbyists can keep up to 25 of them in a 20-gallon. With this amount of fish, you should see them school regularly, a feature highly sought after by hobbyists and professional aquascapers.

An Ember Tetra
An Ember Tetra

Bluefin Notho

Bluefin Notho, similar to the Rocket Clown, is a freshwater killifish known for its vibrant coloration. Unfortunately, males are the ones seen displaying the bright orange coloration pursued by hobbyists, and they tend to be quite aggressive.

We recommend only keeping one of them in a 20-gallon tank, but for hobbyists with a backup tank, you may be able to keep 2 males in a 20-gallon. If you choose to do so, you'll want to regularly monitor them for signs of aggressive behavior. Similar to the Rocket Clown, a tight-fitting lid is a must for the species.

A Bluefin Notho
A Bluefin Notho

Dario hysginon

We've seen plenty of gorgeous aquatic species from Myanmar, such as the Celestial Pearl Danio and Sulawesi shrimp. Another fish is the Dario hysginon, a small-sized red aquatic fish that makes an excellent 20-gallon addition.

These fish are incredibly rare. Breeders looking to get their hands on a male/female pair will be happy to know that the fish can breed in captivity, although raising the fry can be quite difficult.

A male Dario hysginon
Magdalena Teterdynko/Shutterstock.com
A Male Dario hysginon

Emperor Tetra

Emperor Tetras are bold, active fish that have a lot of personality. These fish are much larger than the previously mentioned Green Neons and Embers, and adults can reach about 2 inches in length.

These fish are known to constantly swim around the water column, always on the hunt for their next food source. Hobbyists will appreciate their dark purple coloration and should have no issues keeping up to 8 of them in a 20-gallon tank.

An Emperor Tetra
7TP (Krzysztof Bartosik) / Wikimedia Commons
An Emperor Tetra


That concludes our list of 20 of the best fish for a 20-gallon tank. Whether it's rams, dwarf cichlids, or tetras, you have no shortage of options to choose from for a tank this size.

Now that we've recommended a few choices, which do you think you'll choose? Let us know in the comments, and be sure to visit our marketplace, where you can acquire some of these fish from hobbyists just like yourself.

Image of Miles Harrison

Miles Harrison

With over a decade of aquarium experience, Miles can be found writing about saltwater and freshwater aquariums. When he’s not writing about fish, you can find him going for a run or building websites, such as this one!