The Threadfin Rainbowfish (Iriatherina werneri)

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The Threadfin Rainbowfish, scientifically known as Iriatherina werneri, is a captivating freshwater fish due to its vibrant colors and elongated, thread-like fin extensions.

Ideal for community aquariums, they come in various shades, including blue, red, and yellow.

These peaceful fish are great for beginners and thrive in well-maintained tanks with space to swim and hide.

They add beauty and charm to any aquarium.

Quick Facts

Species Summary

The Threadfin Rainbowfish, also known by its scientific name Iriatherina werneri, is a small and colorful fish that originates from the freshwater streams and rivers of northern Australia and southern New Guinea.

These fish are known for their vibrant colors and thread-like fins, which give them their unique name.

They are relatively hardy and easy to care for, making them a popular choice among aquarium enthusiasts.


The Threadfin Rainbowfish is a small fish, with adult males reaching a maximum size of around 2.5 to 3 inches (6 to 8 centimeters) in length.

The females are slightly smaller, growing to about 2 inches (5 centimeters).

These fish have elongated bodies with a slender shape, and their most striking feature is their thread-like dorsal and anal fins, which give them a delicate and graceful appearance.

The males display vibrant colors, with a metallic blue-green body and bright red or orange accents on their fins.

In contrast, the females are less colorful, usually sporting a silver or pale yellow body.

As with many fish species, the males are more visually striking to attract mates during the breeding season.


The average lifespan of Threadfin Rainbowfish is around 3 to 5 years when kept in optimal conditions.

However, with proper care and attention, these fish can live up to 7 years or more.

Provide them with a suitable environment and meet their specific needs to ensure they live a long and healthy life.

Behavior & Temperament

Threadfin Rainbowfish are known for their peaceful and friendly temperament, making them an excellent addition to community aquariums.

They are not aggressive towards other fish species and are generally well-behaved in a community setting.

However, they can be somewhat skittish, so providing them with ample hiding spaces and a peaceful environment is essential.

These fish are highly sociable and thrive in small groups.

It is recommended to keep at least 6 to 8 Threadfin Rainbowfish together to mimic their natural behavior and provide them with a sense of security.

They are active swimmers and prefer open swimming areas with plenty of room to move around.

It is advisable to avoid overcrowding the aquarium to allow them to swim freely.


Caring for Threadfin Rainbowfish is relatively straightforward, making them suitable for both beginners and experienced fishkeepers alike.

It is important to provide them with a species-appropriate tank setup and meet their specific requirements for water parameters, diet, and tank mates.

Tank Size

To accommodate a small group of Threadfin Rainbowfish, a minimum tank size of 20 gallons (75 liters) is recommended.

This size allows ample space for swimming and provides enough territory for the fish to establish hierarchies without feeling cramped.

However, if you plan to keep a larger group or incorporate other fish species, a larger tank should be considered to maintain a harmonious and balanced ecosystem.

Water Parameters

Threadfin Rainbowfish thrive in water conditions that closely resemble their natural habitats.

Ideally, the water temperature should be maintained between 75 to 82 degrees Fahrenheit (24 to 28 degrees Celsius).

The pH level should range from 6.0 to 7.5, and the water hardness should be kept between 5 to 12 dGH.

Regular monitoring of these parameters is essential to ensure the well-being and health of the fish.

What To Put Inside Their Tank

To replicate the natural habitat of Threadfin Rainbowfish in a home aquarium, it is important to create a well-planted setup with ample hiding spots.

In their native environment, these fish inhabit slow-moving streams and rivers with dense vegetation, so providing them with live plants, driftwood, and rocks is beneficial.

The substrate should consist of fine gravel or sand, resembling the sandy or muddy bottoms of their natural habitats.

Additionally, maintaining gentle water flow using a sponge filter or adjustable water pump is recommended.

Threadfin Rainbowfish prefer calm water conditions and excessive water movement can cause stress and discomfort.

They also prefer lighting that mimics their natural day-night cycle.

Food & Diet

Threadfin Rainbowfish are omnivorous and have a relatively varied diet.

In their natural habitat, they primarily feed on small crustaceans, insects, and plant matter.

In a home aquarium, they can be fed a combination of high-quality flakes, pellets, and live or frozen foods.

Offer a balanced diet that includes protein-rich foods like brine shrimp, daphnia, and bloodworms, as well as vegetable matter like spirulina flakes or blanched vegetables.

Feeding should be done in small portions, 2 to 3 times a day, to prevent overfeeding and maintain water quality.

It is advisable to observe their feeding behavior and adjust the quantity of food accordingly.

Uneaten food should be promptly removed from the tank to prevent water contamination.

Tank Mates

Threadfin Rainbowfish are generally peaceful and can be kept with a variety of other peaceful community fish species.

Some suitable tank mates for Threadfin Rainbowfish include:

When introducing tank mates, it is important to consider their species compatibility, size, and temperament to ensure a harmonious and stress-free environment for all the fish.


Breeding Threadfin Rainbowfish can be a rewarding experience for experienced fishkeepers.

These fish are egg scatterers, meaning they release their eggs into the water where they are then fertilized by the males.

To encourage spawning, provide the fish with a suitable breeding tank setup.

The breeding tank should have plenty of vegetation, such as floating plants or fine-leaved plants like Java Moss, where the female can deposit her eggs.

The water temperature should be slightly raised to around 80 degrees Fahrenheit (27 degrees Celsius) to stimulate breeding behavior.

It is recommended to keep a ratio of one male to two or three females to minimize aggression.

After spawning, the eggs will hatch within a few days, and the fry will become free-swimming shortly after.

It is best to separate the fry from the adults to prevent them from being eaten.

The fry can be fed with powdered fry food or infusoria until they are large enough to consume baby brine shrimp or finely crushed flakes.

Why You Should Consider This Fish

The Threadfin Rainbowfish is a colorful and lively fish that can bring a vibrant touch to any aquarium setup.

With their peaceful temperament and sociable nature, they are great additions to community tanks.

Their unique thread-like fins make them visually striking fish, and their relatively easy care requirements make them suitable for beginners and experienced fishkeepers alike.


Can Threadfin Rainbowfish be kept in a community tank?

Yes, Threadfin Rainbowfish can be kept in a community tank with other peaceful fish species. They are generally well-behaved and not aggressive towards tank mates.

Do Threadfin Rainbowfish require live food in their diet?

While Threadfin Rainbowfish can benefit from live or frozen foods in their diet, they can also be fed a combination of high-quality flakes and pellets. Providing a varied diet that includes both protein-rich and vegetable matter is essential for their overall health.

How many Threadfin Rainbowfish should be kept together?

To mimic their natural behavior and provide them with a sense of security, it is recommended to keep at least 6 to 8 Threadfin Rainbowfish together. However, larger groups can also be kept in larger aquariums.

Are Threadfin Rainbowfish aggressive toward other fish?

No, Threadfin Rainbowfish are generally peaceful and not aggressive toward other fish species. They are known for their friendly and sociable temperament.

How long does it take for Threadfin Rainbowfish to reach sexual maturity?

Threadfin Rainbowfish typically reach sexual maturity around 6 to 8 months of age. However, it is important to note that individual growth rates may vary.

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Irma Bense is the founder of She has over 42 years of experience in keeping fish.She has kept both freshwater and saltwater fish through the years.She has extensive knowledge in breeding numerous species of fish from Show Guppies, Cory Catfish, German Blue Rams to Apistogrammas.You can learn more about Irma on the 'About' page.

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