Nano Fish for Desktop Tanks — Species & Care for 15-20L Aquariums

Nano Fish for Desktop Tanks: A Guide to 7 Species for 15-20 L Aquariums

Limited desk space, or a desire for a small living world you can quietly watch while working or studying — this is exactly what nano fish are for. Species that stay under 2-3 cm as adults can thrive in compact 15-20 L tanks, and their delicate beauty offers an aesthetic that large fish simply cannot match.

This guide introduces seven carefully selected nano fish suited to desktop-sized aquariums, with care notes for each.

---

What Is a Nano Fish?

"Nano fish" is not a scientific classification — it is a term that has become established among aquarium hobbyists. It generally refers to freshwater species with an adult body length of 3 cm or less, most commonly around 2 cm.

Small does not mean easy. In fact, smaller water volumes experience more rapid water quality fluctuations, and many nano species have specific water chemistry requirements (soft water, slightly acidic pH, etc.). Nano fish keeping has a technically demanding dimension: managing a small volume of water with precision.

---

7 Recommended Nano Fish

1. Boraras brigittae (Chili Rasbora / Mosquito Rasbora)

Adult size: 1-1.5 cm (among the smallest vertebrates in the world)

Even at maturity, these fish barely reach 1 cm — a size that defies expectations. Body color is orange to reddish, vivid despite the tiny frame. They are most spectacular in groups: 30-50 individuals create a shimmering cloud of red specks drifting through the water column.

Water parameters: Soft water, slightly acidic (pH 5.5-7.0; hardness 5-10 dGH) Temperature: 24-28 degrees C Care notes: Extremely small — fry can only eat paramecia or infusoria. Even adults require powdered micro-food. Not suitable for community tanks with larger fish.

---

2. Scarlet Badis (Dario dario)

Adult size: 2-3 cm

Jewel-like gradients of red and blue make this one of the most visually striking nano fish available. Prefers live or frozen food (baby brine shrimp, daphnia) and may take time to accept prepared foods, but most individuals can be weaned. Prefers gentle water flow and pairs beautifully with planted aquascapes.

Water parameters: Soft water, slightly acidic to neutral (pH 6.0-7.5) Temperature: 22-27 degrees C Care notes: Males may spar mildly, but confrontations rarely cause injury. Best kept one male per small tank, or in a well-planted setup with sightline breaks.

---

3. Endler's Livebearer (Poecilia wingei)

Adult size: Males 1.5-2 cm; females 3-4 cm

A wild relative of the guppy, males display intense neon coloration in patterns that vary by strain. Hardy, prolific, and beginner-friendly. Smaller and more active than standard guppies; can be bred comfortably in tanks under 20 L.

Water parameters: Neutral to slightly alkaline (pH 7.0-8.0) Temperature: 24-28 degrees C Care notes: Highly productive breeders — population can grow quickly. Do not house with guppies; hybridization will occur and Endler's genetics will be diluted.

---

4. Microdevario kubotai (Blue Neon Rasbora / Neon Green Rasbora)

Adult size: 2-2.5 cm

Fluorescent blue-green body color that becomes electrifying when schooling in groups. Exceptionally well-suited to planted aquascapes — the effect of dozens of blue points of light moving through green vegetation is striking.

Water parameters: Soft water, slightly acidic (pH 5.5-7.0) Temperature: 24-28 degrees C Care notes: Sensitive to water quality deterioration. Regular partial water changes and reliable filtration are essential.

---

5. Chocolate Gourami (Sphaerichthys osphromenoides)

Adult size: 4-5 cm (larger for a nano fish, but worth including)

Deep chocolate-brown body with fine intricate patterning — a strikingly unusual beauty. One of the more demanding nano fish: requires very soft, acidic water and pristine conditions. Intermediate to advanced level, but deeply rewarding for experienced keepers.

Water parameters: Very soft, acidic (pH 4.5-6.5; hardness 3-6 dGH) Temperature: 26-30 degrees C Care notes: Highly sensitive to water quality. RO water and the addition of blackwater extract (peat, catappa leaves) are strongly recommended. Quarantine new arrivals carefully; susceptible to bacterial and parasitic infections.

---

6. Celestial Pearl Danio / Galaxy Rasbora (Danio margaritatus)

Adult size: 2-3 cm

White pearlescent spots scattered across a dark body give this fish its "galaxy" appearance. Works beautifully in planted tanks and can be schooled in aquariums under 20 L. Relatively hardy and accessible for beginners.

Water parameters: Neutral to slightly alkaline (pH 7.0-8.0) Temperature: 22-26 degrees C Care notes: Active swimmers — a tight-fitting lid is essential. Spawns among plant roots and fine substrate; remove eggs or provide a separate breeding tank if raising fry, as adults will eat eggs.

---

7. Microrasbora sp. 'Galaxy' / Pearl Microrasbora

Adult size: approximately 2 cm

A less commonly seen nano rasbora whose body is dusted with tiny pearl-like spots. Native to Southeast Asia, found in drainage ditches and rice paddies in its home range. Relatively easy to keep; a peaceful schooling fish that adds a calm, gently sparkling presence to a small planted tank.

Water parameters: Neutral to slightly acidic (pH 6.0-7.5) Temperature: 22-27 degrees C

---

Choosing a Desktop Tank

Minimum Water Volume Even for nano fish, a minimum of 10 L is recommended. Below this threshold, water quality can shift dramatically within hours. For a desk setup, 15-20 L (approximately 30-36 cm footprint) is a practical and manageable size.

All-in-One Tank Systems Desktop aquariums with integrated filter, lighting, and heater simplify setup and reduce cable clutter. However, some built-in filters produce stronger flow than nano fish prefer — look for models with flow rate adjustment.

Lids Are Essential Most nano fish are capable jumpers. Use a tank with a properly fitted lid. Jump-related fatalities are more common than many keepers expect.

---

Feeding Nano Fish

Standard tropical fish foods are often too large for nano species.

• Powdered food: Required for the smallest species such as Boraras brigittae
• Micro pellets: Suitable for most nano fish; choose pellets under 0.5 mm diameter
• Frozen baby brine shrimp: Excellent for species that prefer live or frozen food
• Paramecia / infusoria: Necessary for the very smallest species and for raising fry

Feed small amounts two to three times per day and remove uneaten food promptly to maintain water quality.

---

Compatibility Considerations

Nano fish are vulnerable to being eaten by anything with a mouth large enough to swallow them. In community tanks, only mix with species of similar size or smaller, with peaceful temperaments. Most nano fish coexist well with dwarf shrimp (Neocaridina, Caridina), though very small shrimp fry may be at risk from even the tiniest fish.

---

On br-choku, specialist breeders list nano fish that rarely appear in retail stores — including rare species, line-bred color variants, and captive-bred individuals conditioned to aquarium life. Before purchasing, ask the breeder about their water parameters and feeding regimen to make your transition as smooth as possible. Find your compact aquatic world on br-choku.