Threadfin rainbowfish
Iriatherina werneri
Males have very long fine fin rays and a small mouth. A very small fish best kept in a quiet group. Its small mouth requires fine food.
At a glance
- Scientific name
- Iriatherina werneri
- Dutch name
- Draadvinregenboogvis
- Water temperature
- 22–30 °C
- pH
- 5–8
- Adult length, up to approximately
- 4 cm SL
- Experience
- Some experience
- General hardness (GH)
- 1–12 °dGH
- Starting footprint
- 60 × 30 cm
- Swimming or living zone
- Midwater
- Flow
- Gentle, with adequate oxygen
This is a documented adult size, not a measured average. SL means body length excluding the tail fin. Sex, origin and cultivated form can affect size.
Care guidance; origin and captive breeding can change requirements. Some ranges are deliberately narrower than natural extremes in the source. Adjust water gradually and keep ammonia and nitrite at zero.
Tank sizes are editorial starting points for adults, not guarantees for a complete stocking plan. Group size, tank height, swimming length and territories may require a larger aquarium.
Origin
New Guinea / Australasia, depending on species — New Guinea / Australia
Habitat & setup
Vegetated freshwater habitats; provide plants and quiet refuges.
Diet
Very small food: fine pellets, small daphnia or newly hatched Artemia. Check mouth-sized portions.
Behaviour & grouping
Group, preferably 8–10 or more.
Living with other animals
Only very small, calm species with matching water needs. Larger fish may swallow this species; a species aquarium is often easier to manage.
Possible combinations to investigate further
- Spotted blue-eye
22–28 °C · pH 5–7
Reproduction
Egg-laying; eggs and fry usually need separate rearing.
A suitable cover helps prevent escape and jumping. Protect intakes for small animals. Do not use copper-based fish medication with invertebrates.
Sources & image credits
Data compiled on: 2026-09-27. Species sources support identity and care; group sources give general starting points. Practical recommendations are an editorial synthesis.
Photo: Iriatherina_Werneri-Male_group.jpg — . CC BY-SA 2.5.