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Passport
- Family
- Rainbowfish
- Grows to
- 4 cm (1.6")
- Lives
- 3–5 years
- Temperament
- Peaceful
- Care
- Intermediate
- Swims
- Near the surface
- Keep
- In a group of 6 or more
- Water
- 22–30 °C (72–86 °F)
IndonesiaPapua New Guinea
Care requirements
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On record for Threadfin Rainbowfish: adult size, lifespan, minimum tank, temperature, ph, hardness, minimum group, diet, care level, swim level, tank length.
A figure that is not on record is left out rather than guessed. One marked Suggested comes from keeping knowledge rather than a page.
- Minimum tank 76 L / 20.0 US gal
- pH 5–8
- Hardness 1–12 dGH
- Diet omnivore
- Tank length 60 cm minimum
Care notes written from general aquarium knowledge, not from the cited sources.
About
Threadfin rainbows are one of the strangest-looking fish in the hobby. The male's fins are drawn out into long black-and-yellow filaments that trail behind and above him like streamers, and when two males display they raise the lot at once — it is an extraordinary thing to watch in a fish this small.
The body itself is nearly transparent with a faint blue sheen, so the fins do all the work. Females are plain and short-finned by comparison.
They're delicate rather than difficult. Tiny, slow, easily out-competed, and needing food graded far smaller than most people would think to offer — but not fussy about water in the way a blackwater specialist is.
Tank setup
Give your threadfins a quiet tank with a still surface. They're slow, deliberate swimmers and anything fast or greedy will out-compete them at every feed.
Keep a group with several males. The displays between rivals are the whole point of the species, and a single male never shows what those fins are for.
Keep the water hard and alkaline. Like other rainbowfish they prefer it, and soft acidic water suits them poorly.
Plant the tank densely with open water in the middle, and add floating cover. They use the upper half almost exclusively.
Cover the tank — they jump — and keep the flow low.
Feeding
Threadfins have minuscule mouths and this is the single most important thing about keeping them alive.
Feed baby brine shrimp, cyclops, microworm, small daphnia and finely powdered dried food. Almost everything sold as "small" is still too large for them.
Feed at the surface. They take food from the top and mid-water and won't chase anything that sinks.
Avoid: standard flake and micro pellets, and avoid housing them with fast feeders, which is the commonest way they slowly starve.
Filtration and flow
Keep the flow very gentle. Those long fins act like sails and a current pushes them around the tank.
A sponge filter is ideal — no intake risk, no strong outlet, and it grows food on its own surface.
Keep the water clean, hard and stable. Regular small changes suit them better than occasional large ones.
With plants
Threadfin rainbowfish are entirely safe with plants and belong in a planted tank.
Fine-leaved plants and floating cover matter most. They give the fish security, and threadfins attach their eggs to fine leaves.
A dark background makes the fin filaments visible, which is otherwise surprisingly difficult given how pale the fish is.
Health
They're hardy in a suitable tank and prone to slow decline in an unsuitable one, with starvation the usual underlying cause.
Check body condition rather than behaviour. A threadfin that has gone thin behind the head is not getting enough food, and the fix is smaller food more often rather than medication.
Damaged fin filaments usually mean a tank mate is nipping. They regrow if the culprit goes.
Breeding
Like all rainbowfish they spawn a few eggs at a time over an extended period rather than in one event.
Eggs attach by fine threads to fine-leaved plants or a spawning mop. Lift the mop every few days into a rearing container and the adults never get the chance to bother them.
The fry are among the smallest of any aquarium fish and they hang right at the surface. They need infusoria or green water delivered at the top before they can manage anything larger, and that first fortnight is where nearly every attempt fails.
Tank mates
Avoid11
- Chinese Algae Eater Chinese Algae Eater is aggressive and Threadfin Rainbowfish is peaceful and easily intimidated.
- Convict Cichlid Convict Cichlid grows to 15 cm against Threadfin Rainbowfish at 4 cm, big enough to eat it.
- Golden Wonder Killifish Golden Wonder Killifish grows to 10 cm against Threadfin Rainbowfish at 4 cm, big enough to eat it.
- Jewel Cichlid Jewel Cichlid grows to 15 cm against Threadfin Rainbowfish at 4 cm, big enough to eat it.
- Pictus Catfish Pictus Catfish grows to 12 cm against Threadfin Rainbowfish at 4 cm, big enough to eat it.
Only with care5
- Betta Betta is a risk to Threadfin Rainbowfish: betta (male) and rainbowfish are a pairing to watch.
- Clown Killifish Threadfin Rainbowfish and Clown Killifish are an uneasy mix: killifish and rainbowfish are a pairing to watch.
- Discus Discus is a risk to Threadfin Rainbowfish: discus and rainbowfish are a pairing to watch.
- Flying Fox Flying Fox is a risk to Threadfin Rainbowfish: flying fox and rainbowfish are a pairing to watch.
- Siamese Algae Eater Siamese Algae Eater is a risk to Threadfin Rainbowfish: flying fox and rainbowfish are a pairing to watch.
No conflict is recorded with the other 88 species in the database, so nothing to flag. 4 species are not covered at all, so they could not be judged either way.