Should I buy it?
Threadfin rainbowfish
Iriatherina werneri
Also known as: threadfin rainbow, feather fin rainbow
A 3.5 cm rainbowfish with spectacular trailing fin extensions on males. Peaceful and very slow-moving. Extremely vulnerable to active tank mates that shred the threadfins.
Threadfin rainbowfish tank mates · 60L tank size hub
peaceful · intermediate care
Sources & confidencehigh · partially verified · beginner: good
Checked against several solid care sources that mostly agree. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Planted nano or community tanks 60L or more with very small peaceful fish and no fin-nippers or strong current.
Avoid if: You keep any fin-nipping species, active danios, or barbs.
Common mistakeHousing threadfins with cherry barbs or tiger barbs because the tank looked peaceful is how keepers invent shredded fin extensions within days. Those long threads are irresistible targets. Keep calm nano neighbours and a real school — not active barbs for ‘interest.’
Top things that go wrong
- Group welfare — not a solo display fish. Plan at least **8** together for normal behaviour; smaller groups often mean stress, colour loss, or nipping depending on species.
- Shrimp & snails. Cherry shrimp and other dwarfs can coexist with peaceful small fish; baby shrimp are food for almost anything that finds them.
What most shops don't tell you
- 1.Myth: threadfin rainbowfish are hardy nano dither that mix with any peaceful barb community. Reality: their fin extensions shred under barb attention — they need a calm softish school of eight or more, not a mixed barb tank for interest.
- 2.Pairs or trios in bare tanks. The fish hide in corners and the threads stay short.
- 3.Sharing the top with hatchetfish or fast surface feeders. Threadfins lose at the flake every time.
- 4.Dither fish and floating plants help confidence. Males are territorial when spawning. Give floor space and broad-leaved structure.
About this species
Threadfin rainbows are 3 to 4 cm surface schoolers from Northern Australia and New Guinea. Adult males grow long thread-like dorsal and anal fins that need a calm tank to stay intact.
- Celebes Rainbowfish80L min · same fish family
- Dwarf Neon Rainbowfish100L min · same group, similar adult size
- Boesemani Rainbowfish150L min · same fish family
- Turquoise / Lake Kutubu rainbowfish200L min · same fish family
- Adolfoi coryalso intermediate peaceful, similar tank size
- Bamboo Shrimpalso intermediate peaceful, similar tank size
- Black ruby barbalso intermediate peaceful, similar tank size
- Brown / hockey-stick pencilfishalso intermediate peaceful, similar tank size
- Cardinal Tetraalso intermediate peaceful, similar tank size
- Celebes Rainbowfishalso intermediate peaceful, similar tank size
No reverse lookups listed yet.
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease56
- Peacefulness82
- Community fit77
- Small-tank fit100
- Hardiness54
- Energy54
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Rough 90L+ layout: one calm centrepiece, 8–12 small tetras/rasboras, 6–8 corydoras-type bottom fish — verify every name in the pair checker before buying.
Safer directions include: Chili Rasbora, Dwarf Gourami, Ember Tetra.
Prioritise 8+ of Threadfin rainbowfish in 60L+ with filtration sized for messy feeding — add only mates that already pass pair checks with this species.
Avoid “one of everything” baskets — Threadfin rainbowfish belongs in a plan built around territory, line-of-sight breaks, and matched water chemistry.
Compatibility
Tank mates for Threadfin rainbowfish
Usually safer (engine GOOD): Chili Rasbora, Dwarf Gourami, Ember Tetra, Sparkling Gourami. Conditional (CAUTION — read the pair page before buying): Betta, Corydoras Catfish, Pygmy Corydoras, Tiger Barb. Avoid (RISKY): African Cichlid, Angelfish, Oscar. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Threadfin rainbowfish + Chili Rasbora
Behaviour and temperament
Threadfin rainbowfish are peaceful top-to-mid schoolers that stay calmer in honest numbers of eight or more. They do not police the tank. Fin damage usually means neighbour choice failed, not a bad strain. Softish water and gentle company keep the threads intact.
What sets them off
- Sudden crowding
- Poor water quality
Fin nipping: Not a habitual fin-nipper; stressed or crowded individuals can still test fins.
Predation: Not a predator toward similarly sized community fish; fry and dwarf shrimp are still fair game for most species.
Territory: Holds a patch (cave, corner, or surface). Break sight lines so neighbours can pass.
Planted tanks: excellent — easy plant ideas
In the glass: typical and warning signs
- Eight or more hold upper midwater with males flashing long fin threads.
- In-school sparkle is normal display, not a reason to break the group up.
- Shredded threads after adding barbs mean the pairing failed — not a one-off accident.
- Scattered, pale fish usually need more of their own kind and calmer neighbours.
- Low listed risk as aggressors; they get bullied long before they bully anyone else.
- They rarely start fights with robust nano neighbours in an honest school.
- Remove barbs or threadfins at the first tear — planting will not reform the mix.
- Increase school size before adding another dither species to fix hiding.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
soft
Diet
carnivore
Threadfin rainbowfish are tiny surface-leaning carnivores with fine mouths. Micro-pellets, crushed foods, and frozen baby brine or daphnia at the film get taken; wafers on the sand rot unnoticed. Feed small pinches they can finish among plants, and keep eight or more so the school holds condition without losing every meal to larger fish.
Shrimp & snails
Cherry shrimp and other dwarfs can coexist with peaceful small fish; baby shrimp are food for almost anything that finds them.
Schooling species — buy 8+ together. Smaller groups stress and lose colour.
- Hold 25 to 30 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 6 to 7.5 and a hardness you can re-test in two weeks. A one-time strip in the shop car park is not a water test.
- Schooling species. Buy 8 or more from the same tank on the same day before adding any centrepiece fish.
- Tank volume meets or exceeds 60L published minimum for adults.
- You can stock at least 8 individuals (group welfare).
- Heater can hold 25–30°C without cooking cooler-water tank mates.
- No known fin-nippers paired with long-finned fish unless you accept documented risk.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 60L minimum tank needs a filter rated for at least 240L/hr turnover and a heater to hold 25–30°C reliably.
Plant suggestions
Threadfin rainbowfish does well in planted tanks. Plants compatible with 25–30°C and pH 6–7.5:
Research: partially verified · Confidence: high · 3 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- Seriously Fish. Iriatherina werneri
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Iriatherina werneri
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Iriatherina werneri
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
Evidence notes
- The Seriously Fish profile for the binomial in this record was successfully reached as the primary aquarium reference.
- FishBase contributes natural-range size and habitat context. Translate those numbers through your heater, your water report, and your tank footprint before stocking.
- Wikipedia is only cited if the article URL returned OK. Use it for orientation, not as the only care sheet for an import.
- All compatibility text reflects typical hobby experience and the Fishori model. Individual fish, shop stress, and the order tank mates are added in can still defy a single-paragraph label.
Common questions about Threadfin rainbowfish
- How big do Threadfin rainbowfish get?
- Threadfin rainbowfish adults reach about 3.5 cm. Shop fish look smaller; stock for the adult length.
- What size tank does Threadfin rainbowfish need?
- 60L is the planning floor for adult swimming space and bioload. A 73L+ tank is the more comfortable long-term footprint. Length and depth matter as much as raw litres for active or territorial fish.
- Are Threadfin rainbowfish aggressive?
- Threadfin rainbowfish are peaceful top-to-mid schoolers that stay calmer in honest numbers of eight or more. They do not police the tank. Fin damage usually means neighbour choice failed, not a bad strain. Softish water and gentle company keep the threads intact.
- Do Threadfin rainbowfish need to be kept in a group?
- Schooling species — buy 8+ together. Smaller groups stress and lose colour.
- What is the most common mistake with Threadfin rainbowfish?
- Housing threadfins with cherry barbs or tiger barbs because the tank looked peaceful is how keepers invent shredded fin extensions within days. Those long threads are irresistible targets. Keep calm nano neighbours and a real school — not active barbs for ‘interest.’
- What fish can live with Threadfin rainbowfish?
- The Threadfin rainbowfish profile lists Chili Rasbora, Dwarf Gourami, Ember Tetra, Sparkling Gourami among its safer pairings (engine-checked GOOD). Betta, Corydoras Catfish, Pygmy Corydoras, Tiger Barb are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid African Cichlid, Angelfish, Oscar (RISKY). Run the pair checker for your exact water and tank size before stocking.