Threadfin Rainbowfish (Iriatherina werneri)

The Threadfin Rainbowfish (Iriatherina werneri) is an elegant and peaceful freshwater fish known for its delicate body, beautiful coloration, and spectacular elongated fins. Mature males develop impressive thread-like fin extensions that they display while interacting with other males and females, making this species an eye-catching addition to planted and peaceful community aquariums.

Peaceful, active, and highly social, the Threadfin Rainbowfish looks especially impressive when kept in a proper group. Males regularly spread and display their elaborate fins, creating a graceful and fascinating aquarium display. Good water quality, gentle filtration, a varied diet, and a well-planted environment help these delicate rainbowfish maintain their best condition and natural behavior.

What We Like About This Fish

• Spectacular elongated, thread-like fins in mature males
• Elegant and graceful swimming behavior
• Beautiful male courtship and display behavior
• Peaceful and social community fish
• Excellent choice for planted aquariums
• Small size suitable for smaller peaceful community setups
• Unique appearance compared with larger rainbowfish species

Recommended Tank Parameters

• Tank Size: Minimum 60 liters (15 gallons)
• Temperature: 24–28°C (75–82°F)
• pH: 5.5–7.5
• Water Hardness: Soft to moderate
• Water Flow: Gentle

A well-planted aquarium with plenty of open swimming space provides an ideal environment for Threadfin Rainbowfish. Dense vegetation, fine-leaved plants, and floating plants can provide security while open areas allow males to perform their impressive fin displays. Strong currents should be avoided because of their delicate fins and relatively gentle swimming style.

Care Guidelines

Diet: Omnivorous. Threadfin Rainbowfish have relatively small mouths and should be offered appropriately sized foods such as high-quality micro pellets, finely crushed flakes, baby brine shrimp, daphnia, and other small frozen or live foods. A varied diet helps maintain healthy growth, coloration, and fin condition.

Social Behavior: Very peaceful and social. Threadfin Rainbowfish should ideally be kept in groups of at least 6, although larger groups provide greater confidence and more natural social behavior. Keeping multiple males can encourage their spectacular fin displays. Avoid aggressive, overly active, or large tank mates that may intimidate them or compete heavily for food.

Origin

Oceania – New Guinea and northern Australia

Average Adult Size

Approximately 4–5 cm (1.6–2 inches)

Average Purchase Size

Approximately 2.5–3 cm (1–1.2 inches)

Schooling Fish

Yes. Threadfin Rainbowfish are highly social fish and should ideally be kept in groups of at least 6. Larger groups can encourage greater confidence, natural social interactions, and more impressive male displays.

Shrimp Safe

Mostly yes. Threadfin Rainbowfish are small and peaceful and generally coexist well with adult shrimp. However, as with most small fish, newly hatched shrimplets may occasionally be eaten. Dense plants, moss, and other hiding areas can help protect young shrimp.

The Threadfin Rainbowfish (Iriatherina werneri) is an excellent choice for aquarists looking for a peaceful, elegant, and unusual small rainbowfish. With its graceful swimming behavior, spectacular elongated fins, and fascinating male displays, this beautiful species can become a standout feature in a mature, well-planted community aquarium.