Home / Fishes / Silversides and rainbowfish / Threadfin rainbowfish
No federal permit to keepThreadfin rainbowfish
Iriatherina werneri
Fishes › Silversides and rainbowfish (Atheriniformes) › Melanotaeniidae (Rainbowfish)
The threadfin rainbowfish or featherfin rainbowfish (Iriatherina werneri) is a rainbowfish, the only species in the genus Iriatherina.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 1.2 in / 3 cm; the largest recorded was 1.6 in).
- Water: Freshwater.
- Temperature: 79–86°F (range recorded for this species).
- pH: 6–8.
- Hardness: 5–12 dGH.
- Layout: Lives on or near the bottom: floor space and hiding places matter more than height.
- Diet: Eats a varied diet: mix quality prepared foods with frozen and live foods. FishBase classes it as a omnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 24 × 12 in (roughly 14 US gallons); space needed is rated “modest tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 72–86 °F, pH 5–8, 1–12 dGH.
- Behaviour: temperament peaceful; a shoaling fish best kept in a group of six or more; suited to a community tank.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Best kept in a densely-planted tank and an excellent choice for the carefully-aquascaped set-up.”
- Diet: “Feeds on floating or suspended phytoplankton, diatoms, and other zooplankton in nature, and in the aquarium must be offered items of a suitable size for its tiny mouth.”
- Tankmates: “Very peaceful but not suitable for the general community aquarium since it's easily outcompeted for food and the long fins of mature males may be nipped at by certain common species.”
- Breeding: “This species is an egg-scatterer exhibiting no parental care and will consume its own eggs and fry given the opportunity.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Rainbowfish
Applies to most species in this group. Habitat: Rainbowfish inhabit Australian and New Guinean freshwaters, including vegetated lake shallows and the slow streams, swamps and billabongs used by threadfins. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- For Melanotaenia boesemani, provide at least 120 × 30 × 30 cm (about 48 × 12 × 12 inches) with open swimming lanes.
- For Iriatherina werneri, use a base at least 60 × 30 cm (24 × 12 inches), planted margins and gentle flow.
- Use efficient filtration and maintenance; threadfins require a mature tank with stable chemistry.
- Boeseman’s rainbowfish are sourced at pH 7.0–8.0 and 10–20 dGH; threadfins at pH 5.0–8.0 and 1–12 dGH.
Diet
- Quality dried foods; finely crush floating foods for threadfins.
- Live or frozen foods sized to the fish’s mouth.
- For threadfins: Daphnia, Moina, Artemia nauplii or copepods.
Social life
- Boeseman’s rainbowfish do best in shoals of at least 6–8. Keep threadfins in at least six, preferably ten or more, with small peaceful fish that neither nip fins nor monopolize food.
Health watch
- Ammonia toxicity.
- Nutritional deficiencies.
Understanding the animal
About this animal
About this animal
It is characterized by long beautiful fins, and is among the most attractive of the rainbowfishes. It is native to freshwater swamps and demersal or thickly vegetated areas of flowing waters, in tropical northern Australia and New Guinea.
Quoted from the Wikipedia article “Threadfin rainbowfish” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater, in rivers and streams, estuaries, mangroves. Stays near the bottom. Inhabits lowland swamps, drainage ditches and streams that have abundant vegetation. |
| Water it lives in | Freshwater, 79–86 °F (26–30 °C), pH 6–8, hardness 5–12 dH. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: open water/substratum egg scatterers. |
What this means for care
- Keep water within its wild range, 79–86 °F.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 91°F (up to 95°F in the hottest sampled areas) |
| Cool-season lows | about 65°F (down to 62°F in the coldest sampled areas) |
| Average temperature | 79–81°F across sampled records |
| Relative humidity | 67–77% on average (driest month about 67%) |
| Rainfall | about 1573 mm a year, with strong wet and dry seasons |
Measured at 31 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The threadfin rainbowfish or featherfin rainbowfish (Iriatherina werneri) is a rainbowfish, the only species in the genus Iriatherina. It is characterized by long beautiful fins, and is among the most attractive of the rainbowfishes. It is native to freshwater swamps and demersal or thickly vegetated areas of flowing waters, in tropical northern Australia and New Guinea. It grows up to 5 cm in length, but this does not include the Threadfin's long tail. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Biology | Inhabits lowland swamps, drainage ditches and streams that have abundant vegetation. Occurs in slow-flowing streams, swampy ponds and billabongs with abundant aquatic vegetation. Temperature and pH ranges are 23°-28°C and 5.2-6.6, respectively. — FishBase |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Adult length
Common length to maximum recorded length. Measured as standard length (snout to the base of the tail, not counting the tail fin). Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Minimum tank footprint
Seriously Fish recommends a tank base of at least 24 × 12 in (about 14 US gallons).
Sources for this sheet
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Seriously Fish — Melanotaenia boesemani Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Seriously Fish — Iriatherina werneri Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
- Merck Veterinary Manual — Disorders and Diseases of Fish Zoo, university or veterinaryAdded in the 2026 source-checked care-guide review.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
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