10 Nano Fish for Freshwater Tanks That Experts Love (and You Will Too)
Looking for the perfect species for your small aquarium? Learn about the top 10 nano fish that are ideal for freshwater tanks under 20 gallons, handpicked by expert aquascaper Mark from MJ Aquascaping. These little fish are full of color, personality, and charm — proving that you don’t need a huge aquarium to enjoy a vibrant slice of nature at home.
Most of these hardy fish can live together because they prefer same conditions, such as warm tropical water around 75–78°F (24–26°C), gentle flow, and soft to moderately hard water. Plus, they all love feeding on tiny foods — including crushed flakes, nano pellets, freeze-dried rotifers, frozen cyclopods, and live baby brine shrimp. Many are peaceful schooling fish that really thrive when they’ve got a group of six or more buddies to keep them company. Keep reading to discover which nano fish takes the top spot and find the must-have species for your next tank setup!
#10 Ember Tetra (Hyphessobrycon amandae)
Ember tetras are a perfect beginner-friendly nano fish, especially if you're just getting into freshwater aquariums. Native to South America, this popular aquarium fish grows to only 0.8 inches (2 cm) and has a nicely rounded body that tapers toward the tail. Ember tetras are also budget-friendly, so you can build a decent-sized school without breaking the bank. While they might appear a little pale at first — especially in store tanks or right after being introduced — they develop a stunning bright orange color once they settle in. You’ll usually find them swimming around the middle to lower levels of the aquarium, so consider pairing them with top-dwelling fish to create a more balanced display.
#9 Rosy Loach (Petruichthys sp. ‘rosy’)
This native species from Myanmar and Thailand is the perfect pick to bring a jolt of energy to your 10- to 15-gallon tank. With their curious personalities, these fish are constantly exploring, filling your aquarium with nonstop action. Imagine a swarm of tiny, torpedo-shaped fish growing to just 1–1.25 inches (2.5–3 cm) and zipping through the water like little hummingbirds. The males are easy to spot with their rich red to orange-brown coloration and bold midline stripe, while females have a more subdued, tannish-gray tone covered in a dusting of small spots. Their lively social behavior and playful chasing makes them to joy to watch as they establish the pecking order within their school.
#8 Green Neon Tetra (Paracheirodon simulans)
If you want a shimmering school of fish that lights up your tank, the green neon tetra is a brilliant pick. Compared to their larger cousins— the cardinal and neon tetras — green neons have a slimmer, more petite build and barely a hint of red, which makes their electric blue-green stripe pop even more. At less than 1 inch (2 cm) long, these peaceful fish are a favorite choice for nano aquariums and look especially impressive in large groups. If they seem a little shy at first, try adding some floating plants or tannin-filled botanicals to slightly dim the tank so they feel less exposed. Another option is to bring in a confident dither fish that will swim around in the open and help them feel more comfortable with their surroundings.
#7 Spotted Blue-Eye (Pseudomugil gertrudae)
Looking for a nano fish that’s both eye-catching and full of character? The spotted blue-eye or Gertrude’s blue-eye brings a burst of activity and beauty to any small aquarium. Hailing from Australia, New Guinea, and the Aru Islands, these lively swimmers reach about 1.25–1.5 inches (3–4 cm) in length and are known for their vivid yellow bodies, glowing blue eyes, and flowy white fins speckled with black dots. It’s so entertaining to see the males showing off by fluttering their pectoral fins and playfully sparring to impress the females. As a top-dwelling species, make sure to use a secure aquarium lid or add floating plants to prevent any unexpected jumps. Plus, feed them plenty of little floating and freeze-dried foods to keep up with their fast metabolisms.
#6 Scarlet Badis (Dario dario)
The scarlet badis is the only species on this list that doesn’t swim in a school, which makes it a perfect little centerpiece for a nano tank. They may look kind of washed out at the store, but once they get settled in your aquarium, the male’s deep red body, vertical striping, and iridescent blue fins make it a real standout. The boys are just under 1 inch (2 cm) while the girls are closer to 0.5 inches (1.25–1.5 cm). Despite their tiny size, they can be a bit feisty toward each other, so in a 10-gallon tank, it’s best to keep only one male by himself or one male with a few females if they’re available. This bottom-dwelling fish moves in a distinctive stop-and-go pattern, darting forward in quick bursts and then pausing, which makes them especially fun to watch as they explore the tank.
#5 Ruby Tetra (Axelrodia riesei)
Ruby tetras are similar in size and temperament to ember tetras but even more colorful in person. Growing to a mere 0.75 inches (1.5–2 cm) long, this South American fish sports a cool-toned red that spreads across its head and upper body, along with a light-colored belly, white-edged fins, and distinctive black dot near the base of its tail. While striking in appearance, these midwater schooling fish can be a bit shy compared to ember tetras and may spend most of their time hiding in the plants. To help them feel more comfortable, we added a small group of blue-eyes as dither fish. These new, outgoing tankmates helped the ruby tetras feel more at ease, and before long, they were swimming out in the open much more often.
#4 Tail Spot Cory (Gastrodermus hastatus or Corydoras hastatus)
This dwarf cory catfish might just be one of the cutest nano fish in the freshwater hobby. Topping out at 1 inch (2.5 cm) long, they come with a rounded snout with tiny barbels, silvery-gray body, and a black diamond-shaped spot at the base of the tail (often surrounded by 2–4 white dots). Unlike most corydoras that only hang out at the bottom, tail spot corys have a wider range and spend a surprising amount of time cruising around the middle of the tank. You’ll still catch them doing classic cory behaviors — like sifting through the substrate, gulping air from the surface, and flashing those quick “winks.” They feel much more secure in a group, so aim for at least 8 to 10 individuals in a slightly larger nano setup, like a 10- to 15-gallon tank. While they are constantly scavenging for leftovers, make sure to feed them a dedicated diet of sinking foods such as wafers, small frozen foods, and live microworms.
#3 Red Neon Blue-Eye (Pseudomugil luminatus)
We can’t resist the gorgeous colors and energy of Pseudomugil rainbowfish and had to add another one to our recommendations. This Indonesian fish also has a bright blue eye and spans about 1.25–1.5 inches (3–4 cm). The males have beautiful red-orange to yellow-orange bodies with tiny black dots on their fins, while females are more muted in color. Both sexes also feature a glowing neon blue stripe along the back. Like the P. gertrudae, the guys are fond of entertaining the gals (and us) by flaring their fins and circling each other in a flashy underwater dance. Many blue-eyes species are relatively short-lived compared to other community fish, so consider breeding them with a floating spawning mop to help maintain a steady supply of new offspring.
#2 Chili Rasboras (Boraras brigittae)
This itty-bitty firecracker is likely the tiniest fish on this top 10 list, making them an excellent choice for nano tanks as small as 3–5 gallons. While green neon and ruby tetras also stay around ¾ inches (1.5–2 cm) in length, this micro rasbora has a very delicate, slender profile that gives it even less mass. Like many nano fish, they tend to look quite faded in the store, but give them 2–3 weeks in your home aquarium and you’ll be shocked as they develop an intense red hue, accented by bold black markings for striking contrast. Because of their petite presence, a bigger group of 8 to 10 fish in front of a lush backdrop of green plants will make their colors truly pop. To suit their miniscule mouths, we’ve had great success feeding them powdered fry foods and live baby brine shrimp.
#1 Celestial Pearl Danio (Danio margaritatus)
Topping the list is Mark’s all-time favorite nano fish: the celestial pearl danio (CPD) or galaxy rasbora. Its space-themed common names are inspired by its shimmering blue-gray body sprinkled with golden stardust, and the males stand out even more with their fiery red-orange fins covered in black striping. To show off their good looks, they’re often seen sparring with each other in hopes of impressing nearby females. This South Asian species is particularly popular among aquascapers because they look like little, 1-inch (2–3 cm) spotted trout darting amongst river reeds and tangled tree roots. Although they can be a bit pricier than other nano tetras, celestial pearl danios are typically easy to find and well worth the investment for the vibrant color and engaging behavior they add to your aquarium.
If you're ready to pick some stunning additions for your tank, take a peek at our selection of live fish available on our website — with new species showing up all the time! For more helpful tips on nano aquariums, explore our related blog posts below and subscribe to our newsletter for the latest updates and expert advice.
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