Should I buy it?
Threadfin rainbowfish
Iriatherina werneri
Also known as: threadfin rainbow, feather fin rainbow, Threadfin rainbow, Feather fin rainbow
Fishori provides conservative planning guidance, not guarantees.
Based on multiple reputable aquarium care sources with strong agreement. Use the numbers here as planning defaults — your room, water, and routine still shape real-world outcomes.
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.
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.
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. Shrimp: compatible in most setups. Cherry shrimp and other dwarf species coexist with peaceful small fish, though baby shrimp are food for almost any fish that gets to them.
Common mistakeThreadfin rainbowfish with cherry barbs or tiger barbs. The long fin extensions are irresistible targets and will be shredded within days.
What most shops don't tell you
- 1.Pairs or trios in bare tanks. The fish hide in corners and the threads stay short.
- 2.Sharing the top with hatchetfish or fast surface feeders. Threadfins lose at the flake every time.
- 3.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 on file yet.
Plan grid
Key limits are shown above; this section adds planning detail: pH band, swim level, bioload and activity, and the radar.
Swim zones
Planning trait chart
Six indices for comparing species on paper before you spend.
- 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.
Common setup sketches
Conservative patterns from Fishori fields — still run the pair checker for every species you add; sketches are not a stocking guarantee.
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.
Safe directions on file include: Chili Rasbora, Ember Tetra, Corydoras Catfish.
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.
Tank mate intelligence
Use the "Often compatible" lists as a shortlist, not a stocking plan. Always run the pair tool and check the footprint of your actual tank first. Verify behaviour for Threadfin rainbowfish against your own reading before you buy.
Pair-level compatibility with this fish as anchor.
Read the blocking rule on each pair page before experimenting.
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Threadfin rainbowfish + Chili Rasbora
Behaviour, temperament, and what to watch
Prose and lists come from the same record: read temperament first, then glass-level signals so you are not surprised after day three.
Threadfin rainbowfish is peaceful in mixed company. Holds territory on substrate, in caves, or at the surface film. Break the sight lines with hardscape to keep the resident off the visitor.
Stress / aggression triggers on file
- Sudden crowding
- Poor water quality
Fin nipping: Not a habitual fin-nipper, but individuals can still test fins under stress or in a crowded tank.
Predation: Not a predator toward similarly-sized community fish. The usual community caveats about mouth size still apply for very small fry or shrimp.
Territory: Holds territory on substrate, in caves, or at the surface film. Break the line of sight with hardscape, and avoid placing the tank where the fish can see its own reflection.
Planted tanks: excellent — easy plant ideas
In the glass: typical and warning signs
- Moderate pacing — not hyperactive, not motionless.
- Shoaling/schooling: most colour and confidence show when the group meets **8+**.
- Clamped fins, gasping at the surface, hiding non-stop, or refusing food after the first week.
- Rapid breathing when parameters swing — fix ammonia/nitrite first, then reassess mates.
- Corner guarding, flaring, or body-blocking — territory is normal until it becomes relentless.
- Separate or rehome if injuries appear, one fish is pinned, or feeding becomes a daily chase.
- If water is stable but behaviour worsens, reduce stocking or remove the highest-impact species first.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Care parameters: water, food, inverts, grouping
Chemistry and group rules sit here so you are not re-reading the same line from tank mate or temperament blocks. Swim level is in the plan grid above.
Hardness
soft
Diet
carnivore
Small invertebrates, frozen bloodworm or daphnia, and protein-rich prepared foods. Rotate the menu and feed by appetite rather than by clock.
Shrimp & snails
Shrimp: compatible in most setups. Cherry shrimp and other dwarf species coexist with peaceful small fish, though baby shrimp are food for almost any fish that gets to them.
Shoaling species. Buy 8 or more of one species together. Smaller schools sulk, lose colour, and redirect their schooling energy at whatever else is in the tank.
Egg scatterers and schoolers still spawn in stable tanks. Have a plan for the fry, or accept that the parents and tank mates will eat them in a community setup.
- 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
Same library as the rest of Fishori: tank-mate index for this species, category peers, guides, and litre-based stocking lists where min tank on file is within the hub volume.
Plan with tools
Pair-level rules and multi-fish stocking use the same conservative engine — add this fish in the tank builder only after mates pass pair checks.
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:
Profile status: partially verified · Evidence tier: high · 3 linked source(s). Fishori does not fabricate citations.
Fishori uses conservative planning rules based on these sources.
Confidence is explained in the summary at the top of this page (same tier as here), not repeated below.
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.
- Fishori profiles work from typical aquarium trade sizes and hobby care norms. Specialist site checks and literature review for this species are not yet recorded here, so the ranges on this page are planning numbers rather than guarantees.