Not furry, but we like them anyway.
Threadfin Rainbowfish
Iriatherina werneri Meinken, 1974
Also called Featherfin rainbowfish
From Southern New Guinea (Merauke area of Papua, Indonesia, to the Fly River in Papua New Guinea) and northern Australia (Cape York Peninsula, Queensland, and Northern Territory), in swamps, lily lagoons and slow streams.123
At a glance the quick version
FishBase: 4 cm SL males, 3 cm SL females; Wikipedia: up to 5 cm body length excluding fin filaments
Looks how to spot one
Scaled, slender nano rainbowfish with long fin filaments
A tiny, slim fish famous for the long, thread-like extensions on the males' fins. Males have the biggest fins and strongest colours, so the sexes are easy to tell apart. When displaying, a male raises his first dorsal fin and flicks his trailing fin threads.31
Personality what they are like
Gentle and peaceful, but shy at feeding time and easily outcompeted, so it does best in a species tank or with other small, calm fish.1
Daily activity how busy a day looks
Moderately active shoaling fish that likes to hang near floating plants and display in open areas.1
Grooming and care the hands-on bits
Needs a mature, stable tank and steady water conditions; Seriously Fish does not recommend it for beginners. Choose tankmates that will not nip the males' long fins.1
Home where they are happiest
Minimum tank base about 60 x 30 cm (around 54 litres). Temperature 22-30 °C, pH 5.0-8.0, hardness 1-12 dGH. Dense planting with floating plants and gentle flow.12
Food basics what goes in the bowl
Has a tiny mouth. In nature it eats diatoms, plankton and tiny crustaceans; in the aquarium offer small live foods such as baby brine shrimp, Daphnia, Moina and microworms, plus finely crushed dry food.123
Company who they like around
Keep at least 6, ideally 10 or more; a ratio of about one male to three females suits breeding.13
The story where it all began
Herman Meinken described it in 1974 from fish collected near Merauke, naming it after the German fish importer Arthur Werner. The genus name combines Irian (Jaya) with the silverside genus Atherina, because it was first thought to be related to silversides.32
Fun facts for the dinner table
- 1
It is the only member of its genus.1
- 2
Its species name honours Arthur Werner, the German aquarium fish trader who collected the first specimens.3
- 3
Males court females with rapid flicks of their dorsal fins and long fin threads.3
- 4
Wild-caught fish are almost never seen in the hobby; nearly all are commercially bred.1
Recognised by the official bits
- IUCN Red List
- Least Concern (assessed February 2019)2
- Taxonomy
- Family Melanotaeniidae; the only species in the genus Iriatherina, described by Meinken in 19741
The care rhythm a typical week and year
A typical home-care rhythm for a Threadfin Rainbowfish. A starting point, not a vet's advice.
- FeedingSmall amounts once or twice a dayevery day
- Temperature checkevery day
- Water changeAbout 25% of the waterevery week
- Water testevery week
- Glass cleanevery week
- Filter rinseRinse in old tank water, never tap waterevery month
Owner questions the things everyone asks
How often should I feed my Threadfin Rainbowfish?
Furry Diary's starting plan is to feed small amounts once or twice a day. Because they have tiny mouths, offer tiny live foods like baby brine shrimp or finely crushed dry food. Always check the food label and ask your vet for exact amounts.123 Pet Wiki plan
What does a Threadfin Rainbowfish eat, and what should it never eat?
In nature they eat diatoms, plankton and tiny crustaceans. In the aquarium offer small live foods such as baby brine shrimp, Daphnia, Moina and microworms, plus finely crushed dry food. Never give large or hard foods that could block their tiny mouths.123
How much space does a Threadfin Rainbowfish need?
A minimum tank base of about 60 x 30 cm (around 54 litres) is recommended. They are active shoalers, so more space is better, especially if you keep a group of 6 or more.12
What temperature, light or water does a Threadfin Rainbowfish need?
Keep the water temperature between 22-30 °C, pH 5.0-8.0, and hardness 1-12 dGH. Provide dense planting with floating plants and gentle water flow. Check temperature daily and test water weekly.12 Pet Wiki plan
How often should I clean a Threadfin Rainbowfish's home?
Furry Diary's plan suggests a weekly water change of about 25%, along with weekly glass cleaning and water testing. Rinse the filter monthly in old tank water, never tap water. Pet Wiki plan
Can a Threadfin Rainbowfish live with others?
Yes, they are gentle and peaceful, but shy at feeding time. They do best in a species tank or with other small, calm fish that won't nip the males' long fins. Keep at least 6, ideally 10 or more, with a ratio of one male to three females.13
How long does a Threadfin Rainbowfish live?
They typically live between 2 and 3 years. A mature, stable tank and steady water conditions help them reach their full lifespan.2
Can I handle a Threadfin Rainbowfish?
It's best not to handle them as they are delicate fish with long fin filaments. Handling can cause stress or injury. Always use a net if you need to move them.13
Written from the sources on this page, a few checked guides (VCA, ASPCA, RSPCA) and Pet Wiki's own starting care plan. A friendly guide, not a vet's advice.
You might also like
Forktail Blue-eye
Spotted Blue-eye
Pacific Blue-eyeWhere this comes from
Every fact on this page has a numbered source. Spotted an error? support@petwiki.app.
- Seriously Fish: Iriatherina werneri (Threadfin Rainbowfish) seriouslyfish.comused for distribution, habitat, tank size, water parameters, diet, behaviour, group size, care level
- FishBase: Iriatherina werneri, Threadfin rainbowfish fishbase.seused for length by sex, water ranges, IUCN status, diet, lifespan, etymology
- Wikipedia: Threadfin rainbowfish en.wikipedia.orgused for other names, history and etymology, size, breeding facts
Checked 2026-09-30. Text is written in our own words from these sources.