The 21 Smallest Aquarium Fish in the Trade: My Picks After 25 Years

Last Updated: May 16, 2026

Small does not mean easy. That’s the one thing I want people to understand before they buy their first nano fish. I’ve kept chili rasboras, pea puffers, and pygmy corydoras, and I’ve worked with virtually every fish on this list during my years managing fish stores. The smallest fish in the trade are often the most demanding in terms of water stability and appropriate tank setup. A chili rasbora in bad water is not a hardy fish. It’s a dead fish.

Here’s the other thing people consistently get wrong: tank size. Small fish don’t mean small tanks. A group of nano fish still needs appropriate space and, more importantly, a stable environment. Parameter swings that a guppy shrugs off will kill a 0.75-inch chili rasbora. I push everyone toward a 10-gallon minimum for any nano species, and bigger is always better.

The 21 Smallest Aquarium Fish in the Trade

1. Chili Rasbora

• Scientific Name: Boraras brigittae
• Adult Size: 0.75 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 68 to 82°F (20 to 28°C)
• pH: 4.0 to 7.0
• Group Size: 10+

The chili rasbora is one of the most visually striking nano fish in the hobby, but it’s not a beginner fish. It needs soft, acidic water, a heavily planted tank, dark substrate, and a group of at least 10. In the right setup, the males light up bright red. In the wrong setup (hard water, bright light, small group), they fade, stress, and decline. Build the tank for the fish first. Then add the fish.

2. Green Neon Tetra

• Scientific Name: Paracheirodon simulans
• Adult Size: 1 inch (2.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 75 to 82°F (24 to 28°C)
• pH: 4.0 to 6.5
• Group Size: 10+

The green neon tetra is the smallest of the three Paracheirodon tetras (neon, cardinal, green neon) and the most demanding. It lives in blackwater habitats with very soft, acidic water and does not adapt well to harder, alkaline tap water. In a blackwater setup with dark substrate and tannins, a group of 15 or more produces a genuinely electric display. This is not a fish for standard community tanks.

3. Celestial Pearl Danio (Galaxy Rasbora)

• Scientific Name: Danio margaritatus
• Adult Size: 1 inch (2.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 73 to 79°F (23 to 26°C)
• pH: 6.5 to 7.5
• Group Size: 8+

Discovered in 2006 in a small pool in Myanmar, the celestial pearl danio caused a collecting frenzy that briefly threatened wild populations. It’s widely tank-raised now and fully established in the hobby. Pearl-spotted body, orange-red fins, compact schooling behavior. Males display and compete with each other without causing real damage. Keep a higher female ratio to prevent constant male harassment. Excellent for a planted nano tank with stable parameters.

4. Pygmy Corydoras

• Scientific Name: Corydoras pygmaeus
• Adult Size: 1 inch (2.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 79°F (22 to 26°C)
• pH: 6.0 to 8.0
• Group Size: 8+

The pygmy corydoras is the smallest corydoras species commonly available and one of the few that schools mid-water as well as near the bottom. They’re peaceful, hardy relative to other nano fish, and endlessly active. Keep a group of at least 8. They’re social fish that genuinely need each other’s company to behave normally. Alone or in small groups, they become stressed and inactive.

5. Ember Tetra

• Scientific Name: Hyphessobrycon amandae
• Adult Size: 0.8 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 73 to 84°F (23 to 29°C)
• pH: 5.0 to 7.0
• Group Size: 8+

The ember tetra is a deep orange nano fish that thrives in planted tanks with dark substrate. It’s peaceful, stays small, and is more accessible than chili rasboras in terms of both availability and care. The color is at its best in soft, warm water with a dark background and heavy planting. A group of 10 or more against a backdrop of green plants is a legitimately beautiful setup.

6. Least Killifish

• Scientific Name: Heterandria formosa
• Adult Size: 0.8 to 1.4 inches (2 to 3.5 cm); females larger
• Min Tank Size: 5 gallons (19 L)
• Temperature: 65 to 80°F (18 to 27°C)
• pH: 7.0 to 8.0
• Group Size: 6+

The least killifish is actually a livebearer, not a true killifish, and it holds the distinction of being one of the smallest vertebrates in North America. It’s native to the southeastern United States, tolerates a wide range of temperatures including unheated tanks, and reproduces readily. Population control is the main concern: they breed constantly and a small colony will multiply quickly. Great option for a species-only 5 to 10-gallon setup.

7. Endler’s Livebearer

• Scientific Name: Poecilia wingei
• Adult Size: 1 to 1.8 inches (2.5 to 4.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 82°F (22 to 28°C)
• pH: 7.0 to 8.5
• Group Size: 6+

Endler’s livebearers are small, colorful, and one of the hardiest nano fish available. Males display vivid neon patterns and are constantly active. They breed readily, so plan for population management. Keep males only for a display tank without breeding, or use a heavily planted tank to give fry hiding spots if you want a self-sustaining colony. They’re more robust than chili rasboras or green neon tetras and tolerate harder water better.

8. White Cloud Mountain Minnow

• Scientific Name: Tanichthys albonubes
• Adult Size: 1.5 inches (4 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 60 to 72°F (15 to 22°C)
• pH: 6.0 to 8.0
• Group Size: 6+

White cloud mountain minnows are a cold-water option for hobbyists who don’t want or can’t maintain a heated tank. They’re extremely hardy, school reliably, and have been in the hobby for decades. The only requirement that trips people up is temperature: they don’t do well above 75°F (24°C) for extended periods. In cooler conditions, they’re nearly indestructible and one of the best schooling nano fish for the category.

9. Exclamation Point Rasbora

• Scientific Name: Boraras urophthalmoides
• Adult Size: 0.75 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 82°F (22 to 28°C)
• pH: 4.0 to 7.0
• Group Size: 10+

Named for the exclamation-mark-shaped marking on their flank, these tiny fish are closely related to chili rasboras and have similar care requirements. They prefer soft, acidic water and heavy planting. Not as widely available as chili rasboras but sought out by nano tank enthusiasts who want something slightly different. Same care approach: mature tank, dark substrate, large group.

10. Sparkling Gourami

• Scientific Name: Trichopsis pumila
• Adult Size: 1.5 inches (4 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 82°F (22 to 28°C)
• pH: 6.0 to 7.5
• Group Size: Pairs or small groups

The sparkling gourami is a labyrinth fish that can produce audible sounds during courtship. That’s not marketing: they actually click and purr. They’re stunning up close with iridescent blue spots and red-edged fins. Keep in small groups in a heavily planted tank. Males are competitive but not destructively aggressive. Not a schooling fish, but an excellent nano centerpiece species for tanks where chili rasboras need a companion species.

11. Pea Puffer (Dwarf Puffer)

• Scientific Name: Carinotetraodon travancoricus
• Adult Size: 1 inch (2.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 77 to 82°F (25 to 28°C)
• pH: 6.5 to 8.0
• Group Size: 1 per 10 gallons, or colony with caution

The pea puffer is tiny, bold, and predatory in a way that most people don’t anticipate. It will hunt snails and attack the fins of slower tank mates. It is not a community fish. I kept pea puffers and the level of hunting behavior they display is remarkable for a 1-inch (2.5 cm) fish. They work best in a species-only setup or with very fast, short-finned tank mates. Males establish territories and will fight, so plan space carefully.

12. Norman’s Lampeye Killifish

• Scientific Name: Aplocheilichthys normani
• Adult Size: 1.3 inches (3.5 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 80°F (22 to 27°C)
• pH: 6.0 to 8.0
• Group Size: 8+

The lampeye killifish has iridescent blue eyes that catch light beautifully. It’s an active, peaceful schooling fish that works well in community nano tanks. Not as commonly available as tetras and rasboras, but worth seeking out. Adaptable to a wide pH range and not as demanding as the Boraras species. A good choice for hobbyists who want something less common.

13. False Rummynose Rasbora (Brilliant Rasbora)

• Scientific Name: Rasbora borapetensis
• Adult Size: 2 inches (5 cm)
• Min Tank Size: 20 gallons (76 L)
• Temperature: 73 to 81°F (23 to 27°C)
• pH: 6.0 to 7.5
• Group Size: 8+

Sometimes sold as the brilliant rasbora, this species produces tight schooling behavior similar to the rummy nose tetra but in a more forgiving package. The red tail and black stripe make it visually interesting. Hardy, peaceful, and a reliable community fish for planted tank setups. Not as compact as the nano fish on this list but a useful bridge species for hobbyists moving from nano to community tanks.

14. Licorice Gourami

• Scientific Name: Parosphromenus deissneri
• Adult Size: 1.5 inches (4 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 82°F (22 to 28°C)
• pH: 4.0 to 6.5
• Group Size: Pairs

The licorice gourami is a specialist species for soft, acidic blackwater tanks. Males are stunning in breeding condition with vivid blue striping. They’re not commonly available and require very specific water parameters. For the dedicated nano blackwater hobbyist, they’re a rewarding species. For everyone else, they’re too demanding to recommend without the right setup already in place.

15. Pygmy Hatchetfish

• Scientific Name: Carnegiella myersi
• Adult Size: 1 inch (2.5 cm)
• Min Tank Size: 15 gallons (57 L)
• Temperature: 73 to 81°F (23 to 27°C)
• pH: 5.5 to 7.0
• Group Size: 8+

Pygmy hatchetfish occupy the top 2 inches (5 cm) of the water column almost exclusively. They’re surface-dwelling schoolers that need a tight-fitting lid: they jump, especially when startled. In a planted tank with floating plants and a secure lid, they produce interesting movement near the surface and don’t compete for space with bottom and mid-level species. Soft, slightly acidic water is required.

16. Strawberry Rasbora

• Scientific Name: Boraras naevus
• Adult Size: 0.75 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 68 to 79°F (20 to 26°C)
• pH: 5.0 to 7.0
• Group Size: 10+

The strawberry rasbora is a close relative of the chili rasbora with orange-red spots on a translucent body. Less commonly available but sought out by nano tank specialists. Same care requirements as the chili: soft acidic water, heavy planting, dark substrate, large group. A species worth tracking down if you’re building a dedicated blackwater nano setup.

17. Mosquito Rasbora

• Scientific Name: Boraras brigittae (same as chili; some use for B. merah)
• Adult Size: 0.75 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 70 to 82°F (21 to 28°C)
• pH: 4.0 to 7.0
• Group Size: 10+

The name “mosquito rasbora” is sometimes applied to Boraras merah, a close relative with orange-red body coloration and a black spot near the tail. Care is nearly identical to chili rasboras. Like all Boraras species, they need stability: parameter swings, inappropriate water hardness, or insufficient group size will cause them to fade and decline. In the right setup, they’re excellent nano fish.

18. Clown Killifish

• Scientific Name: Epiplatys annulatus
• Adult Size: 1.5 inches (4 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 72 to 80°F (22 to 27°C)
• pH: 5.5 to 7.5
• Group Size: Pairs or small groups

The clown killifish is a striking surface-dwelling nano fish with blue and yellow striped fins. Males are bolder in coloration. They need floating plants to feel secure and will stay near the surface. They’re not commonly available but are well-suited to a dedicated nano killifish setup. Peaceful with fish too large to be eaten, but will consume very small fry and invertebrates.

19. Green Kubotai Rasbora

• Scientific Name: Microdevario kubotai
• Adult Size: 0.75 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 68 to 78°F (20 to 26°C)
• pH: 6.5 to 7.5
• Group Size: 10+

The green kubotai rasbora is a tiny, neon-yellow-green nano fish that stands out in a planted aquarium. It’s more forgiving of neutral pH than Boraras species, making it slightly more accessible for average tap water. Active schooler, peaceful, and visually unique. Availability can be inconsistent but it’s worth seeking out for a planted nano setup.

20. Scarlet Badis

• Scientific Name: Dario dario
• Adult Size: 0.8 inches (2 cm)
• Min Tank Size: 10 gallons (38 L)
• Temperature: 71 to 79°F (22 to 26°C)
• pH: 6.5 to 7.5
• Group Size: 1 male per tank, or species only with more females

The scarlet badis is one of the most colorful micro fish in the hobby: vivid red and blue striping on males. It’s also one of the fussiest feeders. Most specimens reject dry food and require live or frozen micro prey like daphnia, baby brine shrimp, or micro worms. Males are highly territorial with each other. In a well-planted 10-gallon with a single male and 2 to 3 females, they’re a stunning display fish. Not for beginners.

21. Dwarf Pygmy Goby

• Scientific Name: Pandaka pygmaea
• Adult Size: 0.35 to 0.45 inches (8 to 11 mm)
• Min Tank Size: 5 gallons (19 L)
• Temperament: Peaceful

The dwarf pygmy goby holds one of the claims to the world’s smallest fish title. It’s a Philippine species that moves between freshwater and brackish conditions. Critically endangered, extremely rare in the trade, and barely found outside of specialty sources near its native range. Listed here for completeness. This is not a fish you’ll find at your local fish store.

Nano Fish Comparison at a Glance

What People Get Wrong About Nano Fish

The biggest mistake is equating small body size with easy care. The chili rasbora and green neon tetra are among the most parameter-sensitive fish in the hobby. A beginner who drops them into a new 5-gallon tank will lose them within a month. Small fish have almost no buffer against water quality swings. A mature filter, stable temperature, and appropriate water chemistry are not optional.

The second mistake is understocking. A group of 4 chili rasboras in a 10-gallon is not a thriving nano tank. It’s a stressed group of fish that will fade in color, hide constantly, and decline. The minimum group sizes listed above are not suggestions. They’re the floor.

The third mistake is overstocking because the fish are small. A 10-gallon tank housing 30 nano fish is overcrowded regardless of body size. Bioload is real. Keep the stocking modest and the water changes consistent.

FAQs

Closing Thoughts

Nano fish are one of the most rewarding directions you can take in this hobby. A well-planted 20-gallon with a group of chili rasboras, a school of pygmy corydoras, and a pair of sparkling gouramis is a complete, visually impressive tank that doesn’t require a lot of space or budget. But it does require the right setup and the right water. Skip the shortcuts and these fish will reward you.

The fish listed here vary from genuinely beginner-friendly to specialist-level. Read the care notes for each one before purchasing. Start with ember tetras or endler’s livebearers if you’re new to nano setups. Work toward chili rasboras or green neon tetras once your tank is mature and stable.

For sourcing quality nano fish, Flip Aquatics and Dan’s Fish are reliable options that ship healthy fish with guarantees.