7 Popular Fish You Should Try in a 20-Gallon Aquarium
20-gallon aquariums are one of the most popular tank sizes among fish keepers because they’re small enough to keep in a bedroom but big enough that you can choose from a wide variety of fish to keep. With all these possibilities, check out our favorite freshwater fish to spice up your aquarium with their beautiful colors and interesting behaviors.
This stunning, three-inch fish is the perfect choice if you’ve ever wanted to try keeping Tanganyikan cichlids. These fish can swim upside-down, sideways, vertically and horizontally to avoid hiding places and surfaces. Provide them with lots of rockwork to simulate their natural habitat, and they’ll feel right at home. You can house three to six depending on how much cover you provide. Or, keep one breeding pair in a 20 gallon tank. The Julies are a peaceful, calm fish. They can be paired with other African fish or fish in the same tank.
Julidochromis ornatus (or the golden Julie) is one of the most popular varieties because of its colorful markings and small size.
6. Leopard Danio
Are you looking for an interactive, hyper fish that will say hello and is willing to share his thoughts? Look at the leopard danio! This brightly spotted schooling fish has a similar appearance to a little trout. They come in both short- and long-fin varieties. The great thing about these danios is how resilient they are – they can live at room temperature without a heater and are happy in a wide range of pH and water hardness. You can watch them race around the tank’s top third in a group of six. To prevent them from hogging all the food, pair them with other fast, midwater fish like tetras and rasboras for a highly entertaining aquarium.
Leopard danios are an easy, budget-friendly schooling fish that aren’t as commonly seen as their famous cousin, the zebra danio.
5. German Blue Ram
The German blue ram (or Mikrogeophagus ramirezi) is a boldly patterned fish. A 20-gallon aquarium can hold one male and one or two women. A female has a shorter dorsal ray, pinkish belly and blue spangles within the black spot. The male is bigger, has a longer dorsal fin, pinkish belly, and blue spangles within her black spot. The key thing to remember is that this South American dwarf cichlid likes higher temperatures around 85degF, so keep them with other hot water fish like cardinal tetras and Sterbai cory catfish.
German blue Rams are monogamous, and have a tendency to show parental love for their young. The male is shown on the left and the female on the right in this photo.
4. Harlequin Rasbora
Trigonostigma heteromorpha, another schooling fish, is a popular choice. It can be kept in groups of six to eight. Their distinctive black triangular patch and bright orange coloration really stand out in a lushly planted tank. The fish can grow to two inches in length and is easy to care for. For more information on caring for rasboras, read our full care guide.
Harlequin Rasboras are social animals that prefer to swim in the middle and top of an aquarium.
Apistogramma cacatuoides and Apistogramma agassizii are two of the most popular members of this large genus of South American dwarf cichlids. Much like the German blue ram, Apistos are very colorful, like to hang out in the bottom third of a tank, and prefer warmer temperatures around 82degF. If you offer breeding caves, the female can pair up with her male choice, protect her eggs, care for her young, and will even be able to breed. Help her out by offering baby brine shrimp as fry food and keeping the water quality as clean as possible. Learn more about them in our Apistogramma care guide.
This male Apistogramma cacatuoides has long, brightly colored dorsal fins, whereas his female counterpart is smaller in size and turns yellow during spawning.
2. Panda Corydoras
Corydoras can be kept in 20 gallon tanks. They are smaller than the larger cory catfish species. This peaceful bottom dweller can be kept in cooler temperatures from 72 to 77degF. To scavenge their favorite foods such as Repashy gel food and frozen bloodworms, they use the whiskers or barbels around their mouths. Keep them happy and well-fed, and soon you may see some breeding behavior and sticky eggs covering the tank walls. For more details, read our cory catfish care guide.
Panda cory catfish are a crowd favorite because of their unique black and white coloration.
1. Pseudomugil gertrudae
The smaller rainbowfish is known to have piercing blue eyes and bright yellow bodies. It also has spotted finnage. When you have six or more males, they will display their fins in a showy dance to attract attention. The spotted blue-eye rainbowfish is our favorite because of its unique appearance and interesting behavior. Depending on where you live, they usually command a higher price and may be a little hard to find, but put them in a planted tank or in front of a black aquarium background and they’ll take your breath away.
You can encourage rainbowfish to lay eggs by using spawning mops made of yarn. Then, remove the mop and place the fry in separate tanks.
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