Threadfin Rainbowfish (Iriatherina werneri)

Threadfin Rainbowfish (Iriatherina werneri) are delicate nano showpieces—males trail extravagant fin streamers that ripple like silk through planted aquariums.

Native to New Guinea and northern Australia, they prefer gentle flow, fine foods, and a quiet community of similarly peaceful nano fish.

If your goal is an elegant planted display rather than a rough-and-tumble community, Threadfins deliver unmatched finnage for their tiny size.

Quick care

• Adult size: About 1.5–2 inches body; males fins much longer
• Temperament: Very peaceful, slightly shy schooling fish
• Minimum tank size: 20 gallons long for a mixed sex group
• Diet: Fine flakes, micro pellets, baby brine shrimp, powdered foods for fry
• Water: 74–82°F; pH 5.5–7.5; soft water preferred
• Ideal tank mates: Chili rasboras, pygmy Corydoras, small peaceful tetras; never with fin-nippers

Frequently asked questions

What tank size do Threadfin Rainbowfish (Iriatherina werneri) need?

A 20-gallon long with gentle flow is a classic minimum for a mixed sex group. These delicate-finned rainbows need length to display and space away from boisterous fish. Tall plants and open mid-water lanes look stunning.

How many Threadfin Rainbowfish (Iriatherina werneri) should I keep?

Keep a group of six or more with several females per male so males can display without constant harassment. Small numbers stay nervous. A proper shoal shows off those filamentous fins.

Are Threadfin Rainbowfish (Iriatherina werneri) good with shrimp?

Yes—adult shrimp are excellent companions; mouths are small. Shrimplets may occasionally be eaten. Avoid fin-nippers and large fish that will shred threadfin fins.

What water parameters suit Threadfin Rainbowfish (Iriatherina werneri)?

Soft to moderately hard water, roughly pH 5.5–7.5, and about 72–82°F in a mature tank. Stability and clean water beat extreme softness. They’re more delicate than bigger Melanotaenia rainbows.

What do Threadfin Rainbowfish (Iriatherina werneri) eat?

Fine flakes, micro pellets, and plenty of tiny live or frozen foods (baby brine, cyclops, daphnia). Males’ fin extensions look best on a varied diet. Feed small portions they can catch in mid-water.

Are Threadfin Rainbowfish (Iriatherina werneri) beginner fish?

Better as a second nano species than a first fish—they want mature water and gentle tank mates. Experienced planted-tank keepers do wonderfully with them. Skip rough community tanks.