Rasbora: A Practical Guide to Care, Species, and Tank Setup

A rasbora is a small freshwater schooling fish in the Cyprinidae family, native to streams and blackwater pools across South and Southeast Asia, with most species topping out between 2 and 10 cm. Trouble starts at the pet store, where the same label covers true its, split-off genera like Boraras and Trigonostigma, and even a danio that snuck into the bin. Pick a species that matches your tank size and water chemistry, and a tight school of these fish can become the most active, colorful feature in a planted community setup.

This practical walkthrough sorts the confusing pet-store labels, profiles species worth keeping at home, and walks you through water parameters, feeding, schooling size, and compatible tank mates for a thriving planted community.

The Rasbora Genus and Its Closest Relatives

Cyprinid fish from Asia dominate the freshwater hobby, and rasboras sit comfortably among the most traded of them all. The genus it was first described by Kuhl and van Hasselt in 1823 from collections in Java. Since then, taxonomists have split the original group into several smaller genera, yet aquarium shops still lump many of them under the it label for simplicity.

True Rasboras Versus Look-Alike Genera

True Rasboras (genus it) still include species like the scissortail and various spotted stream-dwellers from Indonesia and Malaysia. Boraras, a genus carved out in 1993, contains the dwarf species that look like tiny gems. Trigonostigma holds the harlequin it and its close cousins, all known for a distinctive black wedge on the body.

Microrasbora is a former catch-all that now overlaps with Boraras, while Celestichthys was briefly used for the galaxy it before it landed in its own genus, Celestichthys margaritatus (now often called Danio margaritatus). Danio species, including the celestial pearl danio, get pulled into the “it” conversation purely because of size and behavior, even though they are not its at all.

How to Tell Them Apart at a Glance

Body shape gives the fastest clue. True Rasboras are slim and streamlined, built for fast water. Boraras species are compact and rounded, almost disc-shaped from the side. Trigonostigma species have a deeper body and that iconic triangular dark patch. Tetras share the small size but lack barbels and usually show an adipose fin.

Quick reference for store visits:

• ▸Fin shape: Rasboras have a short dorsal fin set behind the body’s midpoint; danios often have a longer dorsal set further back.
• ▸Markings: Trigonostigma always shows a dark side wedge; Boraras shows red or orange along the back and sides.
• ▸Size at sale: Anything under 2 cm is almost certainly Boraras, not a true it.
• ▸Behavior: True its hug the midwater; Boraras prefer dense cover along plant stems and the substrate.

Popular Species Worth Keeping at Home

Five species dominate the import lists at most fish stores, and each one fills a different niche in a planted tank. The harlequin it (Trigonostigma heteromorpha) is the most widely traded ornamental fish in the entire group, and for good reason, yet it is technically no longer a true it at all.

Common Species at a Glance

Species	Adult Size	Min. Group	Temperament	Water Preference
Harlequin (Trigonostigma heteromorpha)	4–5 cm	6	Peaceful, midwater	Soft, slightly acidic
Lambchop (Trigonostigma espei)	4–5 cm	6	Peaceful, schooling	Soft, slightly acidic
Chili (Boraras brigittae)	2–3 cm	10+	Shy, nano schooler	Soft, tannin-stained
Scissortail (it trilineata)	10–13 cm	6	Active, fast swimmer	Slightly hard acceptable
Galaxy (Celestichthys margaritatus)	2–3 cm	8+	Peaceful, often territorial as males	Cool, soft to medium

Matching Species to Tank Size

A 5-gallon tank opens up the nano category only. Chili its (Boraras brigittae) and the phoenix it (Boraras merah) thrive at that scale when stocked at 8 to 12 fish. Below 5 gallons, water quality swings too fast for any schooler, so pass on the purchase.

A 20-gallon long is the sweet spot for harlequins and lambchops, giving the school room to swim laps without bumping into the glass. Scissortails demand at least 30 gallons because of their adult length and constant motion. Galaxy its do well in 10-gallon setups with dense plants, though a longer footprint is always better for any schooling fish.

Water Parameters and Tank Conditions That Mimic the Wild

Wild its live in forest streams where leaf litter, peat, and a slow current keep the water soft, slightly acidic, and dim. Replicating those conditions triggers better color, natural behavior, and breeding readiness in your tank.

Target Numbers for a Healthy Tank

• ▸pH range: 5.5 to 7.0, with most species happiest near 6.5.
• ▸Temperature: 22 to 27 °C, stable to within 1 °C over a 24-hour cycle.
• ▸General hardness (dGH): 1 to 8, with breeding stock kept under 5.
• ▸Carbonate hardness (dKH): 1 to 4, low enough to keep pH from swinging.
• ▸TDS: Below 150 ppm for sensitive Boraras species.

These numbers are tighter than what most community fish tolerate, which is why a it tank is best set up with its own water source rather than tap water run through a basic dechlorinator.

Building a Forest-Stream Layout

Start with a dark, fine substrate like aquasoil or sand tinted with driftwood tannins. Add Indian almond leaves, driftwood branches, and a small pile of rocks to break up the line of sight. A dense carpet of plants such as Microsorum, Cryptocoryne, and Java moss gives the school a place to retreat and the females a spot to drop eggs later on.

Dim the lights with floating plants like frogbit or Amazon frogbit. Strong LEDs over a it tank wash out their iridescence and make shy species stay hidden. Aim for 30 to 40 PAR at the substrate and let the floating layer take the edge off.

“Filtration should turn the tank volume 4 to 6 times per hour, but keep the outflow aimed at the glass so the flow diffuses across the back wall rather than pushing the school around.

Feeding Behavior, Schooling Size, and Daily Observation

its are omnivorous micropredators in the wild, picking at insect larvae, small crustaceans, fallen fruit, and soft algae. That varied diet is exactly what brings out their full color in a home tank. A flake-only diet is the fastest way to watch them fade.

What to Feed and How Often

• ▸Staple dry food: Micro-pellets or crushed high-quality flakes, fed once or twice daily in tiny amounts.
• ▸Frozen foods: Daphnia, cyclops, and baby brine shrimp two to three times a week for color and breeding condition.
• ▸Live foods: Vinegar eels, microworms, and newly hatched brine shrimp for fry and conditioning adults.
• ▸Vegetable matter: Blanched spinach or spirulina flakes once a week to round out the omnivore mix.

Feed only what the school can finish in two to three minutes. Overfeeding a it tank drives ammonia up fast, especially in nano setups with limited filtration.

Schooling Size and What It Tells You

At least 6 to 8 harlequins or lambchops swim together before their natural schooling behavior becomes visible. Nano species such as chili its look lost in groups under 10 and often become reclusive or fin-nipped by larger tank mates. Scissortails appreciate groups of 6 but turn bolder in larger schools of 10 or more.

Daily observation catches problems before they kill fish. Pale bodies, clamped fins, and hiding at the bottom usually point to an ammonia spike, a pH crash, or simply not enough school mates. Glass surfing, on the other hand, often means parameters are off or flow is too strong for the species you have.

Stress behaviors usually trace back to feeding gaps, so dialing in diet often steadies the school before stocking decisions.

“A 20-percent water change with matched temperature and pH every week resets most issues before they escalate, especially in tanks under 20 gallons.

Compatible Tank Mates and Community Stocking

its pair well with any fish that shares their water preference and respects their calm schooling rhythm. The wrong tank mate will either outcompete them for food, stress them into hiding, or actively harass their fins.

Safe Community Picks

• ▸Bottom dwellers: Dwarf corydoras (Corydoras habrosus, C. pygmaeus) and kuhli loaches add activity without competing for the same water column.
• ▸Midwater matches: Pencilfish (Nannostomus), ember tetras, and small its of compatible size.
• ▸Surface calm: A small group of sparkling gouramis or honey gouramis stays out of the schooler’s way.
• ▸Shrimp and snails: Cherry shrimp, amano shrimp, and nerite snails add cleanup crew value without threatening the fish.

Tank Mates to Avoid

Tiger barbs, rosy barbs, and most larger danios will nip it fins, especially the long-finned varieties. Big cichlids, even peaceful dwarf species, can swallow a chili it whole. Boisterous gouramis like the three-spot tend to chase anything small enough to corner.

When planning a community tank, match temperament and water preference first, adult size second. A 5-cm it in hard alkaline water will struggle even with a docile tank mate that thrives in those conditions. A 13-cm scissortail in soft acidic water will look washed out next to a fish that lives for that chemistry.

Breeding Egg Scatterers and the Harlequin Exception

Most its are egg scatterers that release their eggs over fine-leaved plants or moss, and the adults will gladly eat every egg they find. The harlequin it breaks the pattern with a rare egg-depositing behavior that anyone attempting to breed them needs to understand first.

How Egg Scatterers Spawn

Set up a separate 5- to 10-gallon breeding tank with a sponge filter, a layer of java moss, and water matching the parameters above. Condition a small group of two females and three males on live food for one to two weeks. Move them to the breeding tank in the evening, and most species will scatter eggs at dawn.

Remove the adults the moment spawning ends. Eggs hatch in 18 to 36 hours depending on temperature, and fry become free-swimming three to four days later. Start with infusoria, then move to microworms and baby brine shrimp once the fry show color.

The Harlequin Rasbora Exception

Trigonostigma heteromorpha does not scatter eggs. The female presses her belly against the underside of a broad leaf and the male wraps around her, fertilizing the eggs as they stick to the leaf surface. A tank with Cryptocoryne wendtii or Anubias barteri gives them the surface they need.

Watch for females swelling with eggs, then introduce a conditioned pair to a planted spawning tank with soft, acidic water at 26 °C. Eggs stay on the leaf, and the adults ignore them, so a quick removal is still wise to keep survival high. Fry management from there follows the same path as the egg scatterers.

A single successful spawn often produces 30 to 80 fry, and raising even half of them gives you stock to trade with local hobbyists or expand your own school.

Final Thoughts

Pick the right species for your tank size, match the water to their wild habitat, and keep the school large enough to feel safe. Everything else, from breeding success to vivid color, flows from those three calls made before you bring the first fish home.

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