Celebes Rainbowfish Care Guide

The Celebes rainbowfish is the hard-water specialist hiding among the community shoalers — a slender, semi-transparent fish with an electric-blue stripe and, in males, twin trailing black sailfins. Despite the cheap price and the 'rainbow' name, it is not a hardy starter fish: it is delicate, slightly skittish, and one of the very few small community fish that genuinely needs hard, alkaline water rather than soft and acidic.

Celebes Rainbowfish at a glance

The sourced figures the welfare engine uses to judge Celebes Rainbowfish — the parseable key facts.

Where it comes from

Marosatherina ladigesi is endemic to a small corner of South Sulawesi, Indonesia — the Maros and Bantimurung area and its river systems — and lives nowhere else on earth. Its home is clear, slow-flowing, well-oxygenated streams and estuaries around limestone foothills, ranging from fresh to mildly brackish near the coast. That biotope dictates the care: it wants hard, mineral-rich, alkaline water with high dissolved oxygen, the opposite of a blackwater tetra tank. It does tolerate a little salt in the wild, but the aquarium does not need any added; treat the brackish fact simply as a signpost toward hard, alkaline water.

Did you know?

• It is a one-genus wonder: Marosatherina is monotypic, so the Celebes rainbow is the sole species in its genus, and the genus name comes from the town of Maros in South Sulawesi.
• Mature males grow twin elongated black fin extensions on the second dorsal and anal fins that flare during display — the 'sailfin' trait that made it a 1930s aquarium favourite.
• It naturally lives from fresh to mildly brackish, high-oxygen estuarine water, yet needs no added salt in the aquarium.
• Almost uniquely among small 'rainbow' and community fish it wants hard, alkaline water and fails in acidic conditions, making it a natural companion for livebearers rather than tetras.
• It is assessed as IUCN Vulnerable, threatened by habitat degradation, pollution, sand dredging and over-collection in its narrow Sulawesi range, with ex-situ breeding programmes now working to safeguard the wild fish — a genuine reason to buy tank-bred.

Tank size — and why

A tank of around 20 US gallons (70–90 litres) with a length of at least 75–80 cm is the practical floor, and bigger and longer is better. The driver is swimming room for an exceptionally active shoal and stable water volume — more volume buffers the parameter swings this sensitive species cannot tolerate — rather than territory. Favour footprint length over height for the open mid-water swimming lane it displays in. A fitted lid is essential: Celebes rainbows are very good jumpers and an open-top tank loses them.

As a guide, a 20-gallon tank comfortably suits about 6–7 Celebes Rainbowfish as a single-species display, leaving room for tankmates.

How big does it really get?

Full-grown Celebes Rainbowfish reach about 8 cm (3.1 in) long, but they are usually sold at only about 2.5 cm (1 in) — a typical shop size (estimate). At full size, Celebes Rainbowfish needs roughly a 20-gallon tank, about 76 cm long; a common 10-gallon starter kit is only about 51 cm.

Adult size is sourced; the shop size is a typical-juvenile estimate; tank length is approximate for a standard 20-gallon aquarium.

Water parameters in practice

This is the field that makes or breaks the fish. It needs hard, alkaline water — about pH 7–8 and roughly 10–20 dGH — and the sources are blunt that it 'will not do well in acidic conditions'. That is the reverse of most soft-water community fish, and pairing it with a blackwater tetra setup is a chemistry mismatch that slowly kills it. Note the hardness specifically: our species data records pH but not GH, so the medium-to-hard requirement has to be carried in the keeper's head, not read off a chart. Temperature runs 22–28 °C, ideally the warm end around 25–28 °C. Above all it is very sensitive to rapidly changing water and needs a mature, cycled, pristine, stable tank with weekly partial changes — never a freshly set-up one.

Diet & feeding

An easily-fed omnivore that accepts most dried, frozen and live foods, so a good micro flake or small granule makes the base. Vary it with small live or frozen foods — baby brine shrimp, bloodworm, daphnia, cyclops — and the colour deepens; a little blanched veg or spirulina rounds it out. Feed small amounts once or twice a day and keep it sparing, because this species needs the pristine water that overfeeding undermines. One welfare point matters at feeding time: it is an active mid-water feeder with a small mouth and is easily out-competed by faster, pushier fish, so make sure it actually gets its share — a real reason to avoid boisterous tankmates.

Gear & setup

Set it up heavily planted with floating plants to dim the light and open swimming lanes left clear, which is the classic recommendation that brings out its colour. Hard, mineral-rich water can be supported with the right substrate or supplements, and good aeration with gentle-to-moderate flow suits its high-oxygen stream origin. It needs a heater to hold the warm 25–28 °C ideal, and pristine water from regular partial changes is non-negotiable for a species this sensitive. The most important single piece of gear, though, is a well-fitted lid — these are determined jumpers.

Temperament & behaviour

Very peaceful and suitable for many community aquaria, but quite skittish — that timidity is the defining behavioural trait. It is not territorial and not a fin-nipper; males show off with mild display rather than real aggression, and a group will occasionally bicker harmlessly among themselves. The risk is the other direction: a shy, easily-startled fish loses out to boisterous or fast tankmates, then hides, fades and under-eats. In a calm tank with calm company it becomes bold and colourful; in a busy or nippy one it spends its life stressed in the plants.

Group & social needs

Keep a shoal of at least six, and eight to ten or more is the real target. Sex ratio matters: aim for two to three females per male, which spreads out male courtship and display and reduces stress on individual fish. A larger group with a female-skewed ratio cuts the skittishness, improves colour and male display, and dilutes any low-level squabbling. Too few fish, or too many males, leaves you with timid, faded, stressed rainbows.

Compatible tank mates (preview)

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

• Amano Shrimp — Peaceful temperament, similar adult size.
• Bamboo Shrimp (Wood/Fan Shrimp) — Peaceful temperament, similar adult size.
• Boesemani Rainbowfish — Peaceful temperament, similar adult size.

A note on the shrimp and snails here: Celebes Rainbowfish 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 Celebes Rainbowfish's tankmate surface for now — a dedicated tank-mates guide can follow for high-demand species.

Breeding & sexing

Easy to spawn but tricky to rear — the opposite of a difficult fish to get into condition. Sexing is simple: males are larger, darker and more colourful, with elongated black extensions to the second dorsal and anal fins, while females are smaller, paler and short-finned. They are continuous egg-scatterers, depositing adhesive eggs among fine-leaved plants in the same hard, alkaline, pristine water they live in, and in favourable conditions can spawn almost nonstop for months. The parents eat the eggs, so use a separate tank or spawning mops. Eggs hatch over a notably long incubation of roughly five to eleven days, and the tiny, sensitive fry need infusoria or powdered food before graduating to baby brine shrimp.

Lifespan

Around four to five years in a well-maintained aquarium, with no well-documented record much beyond that. The single biggest factor that shortens it is unstable, fluctuating water, followed by acidic or soft water, immature or uncycled tanks, and the chronic stress of being kept with boisterous tankmates that out-compete it for food.

Common mistakes

• Assuming it is a hardy beginner rainbow. It looks easy and cheap but is sensitive to swings and needs a mature, stable tank — the number-one conceptual error.
• Keeping it in soft, acidic water. It needs hard, alkaline water (pH 7–8, around 10–20 dGH) and will not do well below neutral; a blackwater or soft-water community is a chemistry mismatch.
• Adding it to a new, uncycled or fluctuating tank. It needs stable, pristine, mature water, and immature tanks kill more Celebes rainbows than anything else.
• Too small a group or the wrong ratio. Fewer than six, or too many males, leaves them skittish and faded; keep six to eight or more with about two females per male.
• Boisterous or nippy tankmates. Their delicate trailing fins get nipped and they get out-competed for food, so avoid tiger barbs, nippy tetras and pushy fast fish.
• No lid. They are good jumpers and an open-top tank loses fish.

Signs of trouble

• Fading colour and skittish dashing — usually a water-quality, stability or stress signal in this sensitive fish.
• Clamped or torn fins — often the result of nippy or boisterous tankmates harassing the delicate sailfins.
• Hiding, isolation from the shoal and reduced feeding — early stress cues, frequently from being out-competed for food.
• White spot, fungal or bacterial fin and skin infections — stress-triggered ailments that appear when water quality slips or the fish is bullied.

Is this fish right for you?

Don't buy Celebes rainbows if your tank is new or uncycled, if your water is soft and acidic and you can't or won't harden it, if you keep a boisterous or fin-nipping community, if you can't house a group of six to eight or more, or if you want a forgiving fish that tolerates neglect. On stock quality, the species is IUCN Vulnerable with a tiny endemic range, so prefer tank-bred specimens — now produced in quantity — over wild-caught fish to relieve pressure on the wild population. There are no dyed or balloon morphs to avoid here; the real welfare error is buying wild stock or buying for an unsuitable soft-water or boisterous tank.

Bringing one home

Acclimatise slowly — this species is very sensitive to rapid changes, so drip-acclimate over a generous period rather than a quick float-and-tip, and never drop it into a brand-new or fluctuating tank. Add it only to a mature, cycled, hard, alkaline, stable aquarium, and quarantine new stock before it joins the shoal.

Common questions

Are Celebes rainbowfish hardy or good for beginners?

No — they look easy and cheap but are genuinely sensitive. They need a mature, stable, hard, alkaline tank and react badly to parameter swings and immature water, so they are best for a keeper who can provide settled conditions rather than a first fish.

What water do Celebes rainbowfish need?

Hard, alkaline water — about pH 7–8 and roughly 10–20 dGH — at 22–28 °C, ideally the warm end around 25–28 °C. They will not do well in soft, acidic water, which is the opposite of most community tetras, so this is the key thing to get right.

What are good tankmates for Celebes rainbowfish?

Calm fish that share hard, alkaline water: other peaceful rainbowfish, livebearers such as mollies, platies and guppies, and small peaceful gobies or halfbeaks. Adult dwarf shrimp are generally safe. Avoid fin-nippers and boisterous, fast feeders like tiger barbs that damage their fins and out-compete them.

How many Celebes rainbowfish should I keep?

At least six, and eight to ten or more is better, with about two females per male. A larger, female-skewed group is bolder and more colourful, while too few fish or too many males leaves them skittish and faded.

How do you tell male from female Celebes rainbowfish?

Easily. Males are larger, darker and more colourful and develop elongated black extensions to the second dorsal and anal fins, while females are smaller, paler and short-finned.

Do Celebes rainbowfish need salt or brackish water?

No. They range into mildly brackish estuary water in the wild and tolerate a little salt, but the aquarium needs none added. What that wild fact really signals is that they want hard, mineral-rich, alkaline water.

Sources & confidence

Sources & confidence (9 species)

These back the Celebes Rainbowfish 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.

• Celebes Rainbowfish Marosatherina ladigesi — Seriously Fish (seriouslyfish.com/species/marosatherina-ladigesi) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Bamboo Shrimp (Wood/Fan Shrimp) Atyopsis moluccensis — Aquariadise (aquariadise.com/caresheet-bamboo-shrimp-atyopsis-moluccensis) high confidence
• Boesemani Rainbowfish Melanotaenia boesemani — Seriously Fish; Aquarium Co-Op Boesemani guide high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) high confidence
• Bristlenose Pleco Ancistrus sp. — Aquarium Source / aqua-fish.net Ancistrus care guides high confidence
• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) high confidence
• Checker Barb Oliotius oligolepis — Seriously Fish — Oliotius oligolepis (https://www.seriouslyfish.com/species/oliotius-oligolepis/) high confidence

Care-guide sources (7)

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 — Marosatherina ladigesi — authority (Ahl 1936), family Telmatherinidae, max 8.0 cm SL, temp 22-28 C, pH 7.0-8.0, dH 9-19, South Sulawesi (Bantimurung) endemic, IUCN Vulnerable (2019), trophic level 3.1, 'easy to breed', optimum ~pH 7 / 12 dH / 25 C
• Seriously Fish — Marosatherina ladigesi — biotope ('clear, slow-flowing streams... estuarine areas'), 8 cm SL, 30x12x12 in/70 L, temp 22-28 C, pH 7.0-8.0 ('will not do well in acidic conditions'), hardness 10-25 H ('medium to hard... alkaline'), brackish-tolerant but no salt needed, shoal of 6-8+, 2-3 females per male, 'very sensitive to rapidly changing water', slow acclimatisation, male sailfin extensions, egg-scatterer, eggs hatch 5-10 days
• Wikipedia — Celebes rainbowfish — Ahl 1936, synonym Telmatherina ladigesi, monotypic genus, males 6-8 cm / females 5-7 cm, Maros Sulawesi range, fresh-to-brackish high-oxygen streams, transparent body + blue stripe + male black fins, continuous spawning, eggs hatch up to 11 days, IUCN Vulnerable
• Aquadiction — Celebes Rainbowfish — lifespan up to 5 yr, ~8 cm, min tank 75 L (active + jumper), temp 22-27 C, pH 7.0-8.0, GH 10-25, peaceful/timid, group 6-8+, 2-3 females/male, tankmates (rainbows, livebearers, gobies), avoid fin-nippers (delicate fins), egg-scatterer, 'susceptible to disease'
• Fish Laboratory — Celebes Rainbowfish Ultimate Guide — lifespan ~3-5 yr, ~7.5 cm, min 20 gal (experts 50-60), temp 22-28 C, pH 7-8, GH 12-18 dGH, peaceful/shy, group 5-6+, tankmates (livebearers, gobies, halfbeaks; avoid barbs/bettas/cichlids/nippy tetras), 'very sensitive to any changes', not beginner-friendly, 'very good jumpers... fitted lid'
• aqua-fish.net — Celebes Rainbowfish Care Guide — temp 25-28 C, pH 7-8, hardness 10-20, tank 80-100 L with length >=80 cm, group 6+, middle levels, egg-scatterer adhesive eggs, eggs hatch 5-10 days, fry (infusoria then baby brine), lifespan 4-5 yr, 'sensitive to fluctuations... stable, pristine water'
• Ex-situ conservation of the Sulawesi rainbowfish — BIO Web of Conferences (2025) — peer-reviewed review confirming IUCN Vulnerable status, endemism to South Sulawesi (Walanae-Cenranae watershed), and ongoing ex-situ/domestication conservation efforts

More on Celebes Rainbowfish

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 →