Threadfin Rainbowfish

Iriatherina werneri

Also sold as Iriatherina

Synonyms Threadfin rainbow · Featherfin rainbowfish

Threadfin Rainbowfish (Iriatherina werneri) is a peaceful freshwater fish that reaches about 4 cm (1.6 in) and swims in open water in a shoal. It wants 75–82°F (24–28°C) and pH 5.5–7, is kept in groups of 8 or more, and needs a tank of at least 50 L (13 gal).

At a glance

Type	Fish
Adult size	4 cm (1.6 in)
Minimum tank	50 L (13 gal)
Group size	8 or more
Temperature	75–82°F (24–28°C)
pH	5.5–7
Temperament	Peaceful
GH	2–10
Lifespan	3–4 years
Eats shrimp	Shrimplets only

Before it goes in

Threadfin Rainbowfish needs at least 50 L (13 gal). The smallest size in this library that clears that is the 15 Gallon.
Keep 8 or more. Below that it hides, colours down and is far more likely to be picked on.
Adult shrimp are safe; shrimplets will be eaten, so a shrimp colony will not grow in the same tank.
It is the wrong size to share a tank with Goldfish, Angelfish and Axolotl: it ends up as food.
It holds at 75–82°F (24–28°C). That shares a window with Betta and Cherry Shrimp, but not with Goldfish and Dojo Loach.
It jumps. An open-top tank needs a lid or a low water line.
Sources say not to put it in a newly set-up tank — give the tank a few months first.
A group of 8 takes up roughly 68% of what a 15 Gallon will comfortably hold, so plan the rest of the stock around it.

What tank size does it need?

At least 50 L (13 gal). The smallest size here that clears it is the 15 Gallon.

How many should I keep?

8 or more. Fewer than that and it spends its time hiding instead of out in the open.

Will it eat shrimp?

Adults are safe, shrimplets are not. You can keep shrimp with it; you just will not get a growing colony.

What water does it want?

75–82°F (24–28°C), pH 5.5–7, GH 2–10.

How long does it live?

3–4 years in a tank that suits it. That is how long you are signing up for.

Can it go in a new tank?

No. Sources say not to add it to a newly set-up tank — it wants a tank that has been running for months.

Good tank mates

Tank mates from this library that share its temperature window, are peaceful and eat neither it nor its young: Cherry Shrimp, Bristlenose Pleco, Celestial Pearl Danio, Molly and Otocinclus.
Plants that hold up with it: Hygrophila corymbosa 'Siamensis', Water Sprite, Anubias nana 'Petite' and Cryptocoryne wendtii.

Often compared with

	Threadfin Rainbowfish	Forktail Rainbowfish	Dwarf Neon Rainbowfish
Adult size	4 cm	5 cm	6 cm
Min tank	50 L	50 L	80 L
Group	8+	6+	6+
Temperature	75–82°F (24–28°C)	75–82°F (24–28°C)	73–82°F (23–28°C)
Eats shrimp	Shrimplets only	Shrimplets only	Yes

More livestock

Plan a tank with Threadfin Rainbowfish →

Sources (4) · checked Sep 2026