Scarlet Badis Care Guide

The scarlet badis, Dario dario, is the smallest fish in this encyclopedia - males around 2 cm, females barely 1.3 cm - and one of the most mis-sold "easy nano fish" in the hobby. The defining fact is its diet: it is a fussy micropredator that usually refuses flakes and pellets and slowly starves on dry food, which is why it is so often reported "dying of unknown causes." Add that it is shy, easily out-competed and prey to ordinary community fish, and the honest verdict is plain - this is not a beginner fish.

Scarlet Badis at a glance

The sourced figures the welfare engine uses to judge Scarlet Badis — the parseable key facts.

Where it comes from

It comes from the Brahmaputra drainage of West Bengal and Assam in India, where Seriously Fish describes shallow, clear-water streams with sand or gravel substrates and dense growths of marginal and aquatic vegetation, and FishBase records crystal-clear water around 26 C over a sand or fine-gravel bottom. That biotope dictates the whole setup. The dense-plant micro-habitat means a heavily planted, mature nano tank with broken sightlines, so a shy fish feels safe and males can hold mini-territories. The invertebrate-rich vegetated streams mean a micro-invertebrate diet - the single most important care fact below. The clear, gently flowing water means low flow, clean and stable parameters; this is not a high-flow or messy-tank fish.

Did you know?

• It is one of the world's smallest aquarium fish - mature males around 2 cm and females about 1.3 cm, a full-grown fish smaller than many other fishes' eyes.
• It is a jewel that has to hunt: unlike most starter fish it keeps the wild micropredator habit, hunting live prey and largely ignoring processed food.
• It doubles as living pest control - in a mature planted tank it grazes tiny nuisance invertebrates and is sometimes used to help control micro-pests.
• The male's roughly seven iridescent bars intensify when he is dominant and courting - a built-in mood ring of rank.
• It is assessed by the IUCN as Data Deficient, and habitat and collection pressure make tank-bred stock the responsible choice.

Tank size — and why

Around 10 US gallons is the usual minimum, or Seriously Fish's 45 by 30 cm footprint for a pair or one male with several females. The reasoning is not swimming volume - a 2 cm fish needs almost none - but stability and territory. A tiny micropredator needs a biologically mature tank with stable parameters and grazeable micro-fauna, and enough planted cover for males to hold non-overlapping mini-territories and for shy individuals to feel secure. A small, immature, swinging tank is the danger, so mature it before the fish go in.

As a guide, a 20-gallon tank comfortably suits about 1 Scarlet Badis as a single-species display, leaving room for tankmates.

See it to scale

Adult Scarlet Badis reach only about 2 cm (0.8 in) long — close to the size they are sold at, so what you see is roughly what you get. The catch is the group: a proper shoal still needs about a 10-gallon tank, around 51 cm long.

Adult size is sourced; tank length is approximate for a standard 10-gallon aquarium.

Water parameters in practice

Aim for 22-26 C, near-neutral pH 6.5-7.5, and soft to medium hardness; it tolerates more than that on paper - Seriously Fish gives 18-26 C, pH 6.5-8.5 and 18-268 ppm - but soft-neutral is preferred. As with most nano fish the rule is stability over precision: the real risk is a small, immature tank whose parameters swing fast, not any specific pH. Keep ammonia and nitrite at zero, do regular small changes, and mature the tank before stocking. Some keepers use RO-tempered water for stability and breeding. The bioload is very low, but small volumes are unforgiving, so do not over-stock.

Diet & feeding

This is the fish's make-or-break field. In the wild it is a micropredator taking small aquatic invertebrates, crustaceans, larvae and zooplankton among dense plants, and it keeps that habit in captivity - it will most likely not accept traditional flakes or pellets, and on dry food it slowly starves. Feed live and frozen micro-foods: baby brine shrimp (Artemia nauplii), daphnia, cyclops, moina, grindal worms, micro-worms, banana worms and vinegar eels, in small daily portions. Seriously Fish specifically warns against bloodworm and Tubifex, which are linked to obesity and disease in this species. In a mature planted tank it also grazes micro-pests. The load-bearing behaviour is that it is a slow, deliberate, non-competitive hunter that does not actively search for food the way most fish do, so it must never share a tank with faster feeders or it quietly starves.

Gear & setup

Give it fine sand or small gravel, very dense planting, driftwood or rock caves and leaf litter - heavy cover is mandatory for activity and low stress, and a bare tank leaves it pale and hiding. Keep flow low to suit a slow, clear-stream fish. Filtration should be gentle but adequate; because a small volume swings fast, some keepers deliberately over-rate the filter - say a 20-gallon-rated filter on a 10-gallon tank - for stability. Keep the tank covered as standard nano practice.

Temperament & behaviour

It is peaceful toward other species but males are territorial with each other - Seriously Fish notes it is easily intimidated or out-competed, while rival males establish territories and can be highly aggressive toward one another. At this tiny size that conspecific aggression rarely causes physical wounds in a planted tank; the real cost is stress and feeding suppression of the weaker male, not injury. Above all it is incredibly timid and shy, hiding and losing colour in bare or bright tanks or alongside bold tankmates, and bold only in dense cover with calm tankmates or none at all.

Group & social needs

Keep one male, or one male with several females as a small harem, or give multiple males genuine space. Two males in a small tank will spar, and the subordinate hides and stops feeding. It is not a schooling fish. Because the species is so easily intimidated and out-competed, many keepers run it species-only, and that is frequently the kindest option - a dedicated planted nano with no competition at all.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Scarlet Badis and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Assassin Snail — Peaceful temperament, similar adult size.
• Black Neon Tetra — Uses the midwater zone, peaceful temperament, similar adult size.
• Black Phantom Tetra — Uses the midwater zone, peaceful temperament, similar adult size.

A note on the shrimp and snails here: Scarlet Badis is peaceful and generally invertebrate-safe — but almost any fish will take very small shrimplets given the chance, so give shrimp dense cover (moss, leaf litter) if you want a colony to grow, rather than expecting every baby to survive.

This engine-cleared shortlist is Scarlet Badis's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Breeding is moderate: pairs spawn readily, but the challenge is the infusoria-grade first foods for minuscule fry and keeping the adults well-fed and unstressed. Sexing is easy at maturity - males are red and blue, barred, with extended fins, while females are small, drab grey and plain - though juveniles are hard to tell apart. It is a substrate or cave spawner forming temporary pair bonds: a dominant male intensifies his colour and displays to attract a female, spawning is brief, and eggs are scattered or attached on the underside of a leaf, a solid surface, or in dense moss or caves. The male loosely defends the area but provides little real parental care; incubation runs about two to three days, and the fry are extremely tiny, needing infusoria, green water or microworms before they can take baby brine shrimp. A heavily planted, mature tank lets some fry survive without intervention.

Lifespan

About 3-5 years, occasionally up to six with excellent care. The species is notorious for dying of unknown causes, but those sudden losses are rarely a true mystery - they trace to slow starvation on dry food or when out-competed (the number one killer), to stress from bold or large tankmates and bare tanks, to unstable water in a too-small under-filtered nano, or simply to being eaten by a tankmate big enough to swallow a 2 cm fish.

Common mistakes

• Buying it as an easy beginner nano fish. Aquariadise flatly does not recommend it for beginners - it needs exacting feeding, stable mature water, careful tankmates and often a species-only tank.
• Expecting it to eat flakes or pellets. It usually won't, and it starves slowly while looking fine for weeks - the single most common killer.
• Putting it in a general community or with bigger fish. It is out-competed at feeding and is itself prey; it belongs in a gentle nano or species tank.
• Keeping too many males in too small a tank. Males are territorial - keep one male, or one male with several females, or give real space.
• Stocking an immature or unstable small tank. Parameters swing fast in a tiny volume, so mature the tank first and don't over-stock.
• Over-feeding bloodworm or Tubifex. These are linked to obesity and disease in this species; vary the diet with baby brine shrimp, daphnia and grindal or micro-worms.

Signs of trouble

• A thin, sunken or pinched belly - almost always under-feeding or out-competition, not exotic disease.
• Colour loss and greying - stress from bold tankmates, a bare tank, or unstable water.
• Hiding and refusing food - the classic prelude to the slow-starvation decline; check that food is reaching it.
• Clamped fins and listlessness - general stress; check temperature stability and water quality first.
• A previously bright male fading and a subordinate male hiding - male-vs-male territorial pressure suppressing the weaker fish.

Is this fish right for you?

Do not buy a scarlet badis if you can't supply small live and frozen micro-foods daily - it usually refuses dry food and starves, which is the trap behind most reported deaths. Do not buy it as a beginner's community fish: it is out-competed by faster feeders and is prey to ordinary community species, so it needs a gentle nano or a species-only tank. Do not put more than one male in a small tank, and do not add it to an immature, swinging nano. On stock, shops display mostly the bright males while the drab females go overlooked, so expect to hunt for females, and pick plump, well-coloured, actively hunting fish - a thin or pale shop fish is a warning sign. It is assessed by the IUCN as Data Deficient with wild-collection pressure, so favour tank-bred stock.

Common questions

Are scarlet badis good for beginners?

No. Aquariadise specifically does not recommend them for beginners. They usually refuse dry food and need live or frozen micro-foods, they are fragile and easily out-competed, and they often do best species-only - this is an experienced nano-keeper's fish.

What do scarlet badis eat - will they take flakes?

They are micropredators that usually refuse flakes and pellets. Feed small live and frozen micro-foods: baby brine shrimp, daphnia, cyclops, grindal and micro-worms. Avoid bloodworm and Tubifex, which are linked to obesity and disease in this species.

Why is my scarlet badis dying or not eating?

Almost always slow starvation or stress, not a mystery illness. As a slow, deliberate hunter it gets out-competed by faster fish and quietly starves on dry food, often looking fine for weeks first. Feed live or frozen micro-foods and keep it with calm, non-competitive tankmates or none.

What can live with a scarlet badis?

Only the smallest, calmest, non-competitive fish - tiny peaceful nano species in a well-planted tank where food reaches the badis - or, better still, a species-only tank. Never house it with bigger fish that will eat a 2 cm fish, or with fast greedy feeders like bettas, danios or most barbs that out-feed it.

How many scarlet badis should I keep?

Keep one male, or one male with several females as a small harem, or give multiple males real space and cover. Two males in a small tank spar, and the weaker one hides and stops feeding.

How big do scarlet badis get?

Tiny - males around 1.5-2.0 cm and females about 1.2-1.3 cm, among the smallest aquarium fish in the hobby. That size is exactly why most community fish treat them as prey.

Sources & confidence

Sources & confidence (9 species)

These back the Scarlet Badis figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Scarlet Badis Dario dario — Aquariadise; Fish Laboratory scarlet badis guides high confidence
• Assassin Snail Clea helena (Anentome helena) — The Shrimp Farm (theshrimpfarm.com/posts/assassin-snail-care) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Cardinal Tetra Paracheirodon axelrodi — Seriously Fish (seriouslyfish.com/species/paracheirodon-axelrodi) high confidence
• Celestial Pearl Danio Celestichthys margaritatus — Seriously Fish (seriouslyfish.com/species/celestichthys-margaritatus) high confidence
• Cherry Shrimp Neocaridina davidi — Aquarium Co-Op cherry shrimp care; The Shrimp Farm high confidence
• Chili Rasbora Boraras brigittae — Seriously Fish (seriouslyfish.com/species/boraras-brigittae) high confidence
• Clown Killifish Epiplatys annulatus — Seriously Fish (Epiplatys annulatus); Aquarium Co-Op high confidence

Care-guide sources (6)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• FishBase - Dario dario — authority (Hamilton, 1822), Badidae, 1.5 cm SL males / 1.2 cm SL females, India, benthopelagic 0-1 m, habitat 'crystal clear...around 26 C', trophic ~3.0, 'Males with 7 prominent dark vertical bars...; females uniform', IUCN Data Deficient
• Seriously Fish - Dario dario — synonyms (Labrus/Badis dario), 12-20 mm SL, Brahmaputra/Assam, 'Shallow, clear water streams...dense growths of...vegetation', 18-26 C / pH 6.5-8.5 / 18-268 ppm, 45x30 cm for a pair or 1 male + females, micropredator needing live/frozen, 'avoid bloodworm and Tubifex', 'easily intimidated or outcompeted', males 'highly aggressive toward rivals', brief substrate spawning, male sole/poor parental care, 2-3 day incubation
• Aquariadise - Scarlet Badis Care Sheet — males ~2.0 cm / females ~1.3 cm, 3-6 yr 'notorious for dying of unknown causes', 10 gal min, 72-79 F, pH 6.5-7.5, over-rated filtration tip, 'will most likely not accept traditional fish flakes or pellets', starvation risk, 'incredibly timid and shy', male territoriality, 1 male/10 gal or 1 male + 2-3 females, bettas out-compete, species-only recommendation, beginner 'Not recommended'
• Fish Laboratory - Scarlet Badis (Dario dario) care guide — corroborates ~2 cm / 0.8 in size, 3-5 yr lifespan, 10 gal planted nano, live/frozen requirement, shy and out-competed behaviour, male territoriality, prey-to-larger-fish, advanced care level
• FantaSea Aquariums - Scarlet Badis care — corroborates tiny size, micropredator diet, dry-food refusal, shyness, gentle-tankmate / species-only guidance
• Aquarium Source - Scarlet Badis 101 — corroborates ~1 in size, 3-5 yr lifespan, live/frozen feeding difficulty and starvation risk, timid temperament, careful tankmate selection

More on Scarlet Badis

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →