Pseudomugil signifer (Butterfly Rainbowfish)

16 June 2026

730

The Butterfly Rainbowfish, native to the coastal streams of Eastern Australia, is a captivating nano fish prized for its striking blue eyes and elegant, butterfly-like fins. Known for their energetic yet peaceful schooling behavior, they add a lively splash of color and movement to well-planted freshwater or brackish aquariums.

Pseudomugil signifer (Butterfly Rainbowfish)

Overview

The Butterfly Rainbowfish (Pseudomugil signifer), also commonly known as the Pacific Blue Eye, is a stunning and active species of the blue-eye family. Renowned for their mesmerizingly bright blue eyes and the dramatic, sail-like fin displays of the males, these fish are highly sought after by nano aquarium enthusiasts. They bring a dynamic energy to the tank, constantly darting and displaying in their social groups.

Image of butterfly rainbowfish pseudomugil signifer

Distribution and Habitat

Native to the eastern coast of Australia, the Butterfly Rainbowfish has a vast natural range stretching from northern Queensland down to southern New South Wales. Because of this wide distribution, they are found in highly varied environments, ranging from pure freshwater rainforest streams to brackish tidal mangrove estuaries. They typically inhabit clear, slow-moving or moderately flowing waters with abundant submerged vegetation and overhanging plant life.

Description of Butterfly Rainbowfish

The Butterfly Rainbowfish is a small, visually striking fish. While females and juveniles are relatively modest in their appearance, mature males develop spectacular finnage that they flare to attract mates and establish dominance.

Body shape:

They possess a slender, elongated, and slightly laterally compressed body typical of many rainbowfish species, built for quick bursts of speed.

Color:

The body is generally a semi-transparent silver to pale yellow. Depending on the specific regional morph, males will display vibrant yellow, orange, and black margins on their fins. Their scales often reflect an iridescent sheen under good lighting.

Barbels:

This species does not possess any barbels.

Snout:

They have a relatively pointed snout with a small, upward-facing mouth, indicating their preference for feeding on small insects and larvae near the water's surface.

Eyes:

Their most defining feature is their large, strikingly bright blue eyes, which stand out prominently against their body coloration.

Fins:

Males feature highly extended, sail-like dorsal and anal fins. When flared during displays, these fins give the fish a distinct "butterfly" appearance. Females have much shorter, rounded, and transparent fins.

The Tail:

The caudal (tail) fin is moderately forked and often features subtle yellow or orange tinges along the outer edges in males.

Temper

These fish are generally very peaceful and make excellent additions to community aquariums. Males will frequently engage in sparring matches, flaring their fins and swimming in tight circles to establish dominance and impress females, but these interactions are purely for show and rarely result in any physical harm.

Sociality

Butterfly Rainbowfish are highly social, schooling fish. They must be kept in groups of at least 6 to 8 individuals, though larger groups of 10 or more are highly recommended. A proper school makes them feel secure, encourages their best coloration, and promotes natural social behaviors.

Activity

They are incredibly active and energetic, spending the majority of their time darting around the middle and upper levels of the water column. Their constant motion adds a wonderful sense of life to the aquarium.

Keeping and Caring for Butterfly Rainbowfish

Caring for Pseudomugil signifer is relatively straightforward, provided their water quality is strictly maintained. They are adaptable to a range of water conditions but are sensitive to sudden fluctuations and poor water parameters.

Tank size:

A minimum tank size of 15 gallons (approx. 60 liters) is required for a small school. However, because of their active swimming nature, a longer tank (such as a 20-gallon long) is highly preferred to give them adequate swimming space.

Water Parameters:

Due to their wide natural distribution, they are highly adaptable but thrive best in stable conditions.

Temperature

The ideal temperature range is between 22-26°C (72-79°F).

pH

They do well in slightly acidic to moderately alkaline water, with a pH range of 6.5 to 8.0.

Hardness

Water hardness should ideally be between 5 and 20 dGH. They can also tolerate, and sometimes benefit from, a slight addition of marine salt, as many natural populations inhabit brackish water.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept as low as possible, ideally below 20 ppm, through regular water changes.

Lighting

Moderate lighting is best. While they look stunning under bright lights, providing floating plants to create shaded areas will help them feel more secure and bring out their richest colors.

Water flow

They appreciate a moderate water flow that mimics their natural stream habitats, but ensure there are calmer resting areas within the tank.

Decorations and Plants

A heavily planted tank is ideal. Use fine-leaved plants like Java Moss, Hornwort, or Cabomba, which mimic their natural environment and provide hiding spots. Driftwood and leaf litter can also be added to create a natural aesthetic.

Diet

In the wild, they are micro-predators feeding on small insects, crustacean larvae, and zooplankton. In the aquarium, they are unfussy omnivores. Offer them a high-quality micro-pellet or crushed flake food as a staple. Supplement their diet heavily with live or frozen foods such as daphnia, baby brine shrimp, and cyclops to ensure optimal health and coloration.

Some Feeding Tips

Because they have very small throats and upward-facing mouths, ensure all food is appropriately sized and floats or sinks very slowly. Feed them small amounts 2 to 3 times a day rather than one large meal.

Breeding

Breeding the Butterfly Rainbowfish is relatively easy. They are continuous egg scatterers. To breed them, set up a separate breeding tank with a sponge filter and plenty of spawning mops or dense clumps of Java Moss. Condition the adults with high-quality live foods. Females will lay a few eggs daily, which adhere to the plants or mops via small adhesive threads. The parents will readily eat the eggs and fry, so it is best to remove the spawning mops every few days to a separate hatching container. The eggs hatch in about 10 to 15 days, and the tiny fry will need infusoria or specialized liquid fry food until they are large enough to accept freshly hatched baby brine shrimp.

Conclusion

The Butterfly Rainbowfish is a truly rewarding species for both beginner and experienced aquarists. Their breathtaking blue eyes, fascinating fin displays, and lively personalities make them a standout choice for any peaceful, well-maintained nano or community aquarium. By providing them with a proper diet and a clean, planted environment, you will be treated to a spectacular daily show of color and activity.

Fish info

Care level: Easy - Moderate
Temperament: Peaceful
Adult size: 5-7 cm
Life expectancy: 2-3 years
Fish type: Rainbowfish
Temperature : 22-26°C
pH: 6.5-8.0
Color Form: Black, Blue, Clear, Orange, Silver, Yellow

Related on Fishs

Leave your comments

Latest on Fishs

Marble Gourami (Cosby Gourami), Trichopodus trichopterus

Easy - Moderate

Freshwater labyrinth fish

The marble gourami, commonly sold as the Cosby gourami, is a selectively bred color form of the three-spot gourami, Trichopodus trichopterus. It is a labyrinth fish that can breathe atmospheric air and generally occupies the upper and middle levels of a planted aquarium. This species is usually hardy, but adult males may become territorial, particularly when spawning. The supplied images show several color forms, so exact strain identification is not certain; the fish are best treated as marble or related cultivated forms of T. trichopterus.
Marble Gourami, Gold-Orange Form (Trichogaster trichopterus)

Easy - Moderate

Freshwater labyrinth fish

The marble gourami is a selectively bred color form of the three-spot gourami, a labyrinth fish from mainland and island Southeast Asia. The supplied trade label identifies these fish as a gold-orange pair, although commercial names and appearance can vary, so the exact cultivated form is not fully certain. They are generally hardy community fish, but males may become territorial, especially when spawning. Provide warm, stable water, surface access, dense planting, and gentle filtration.
Honey Gourami Gold (Trichogaster chuna)

Easy - Moderate

Small freshwater labyrinth fish

The honey gourami is a small, peaceful labyrinth fish suited to planted freshwater aquariums. The supplied source identifies a gold pair as Colisa chuna, an older name now generally treated as Trichogaster chuna. The photographs show orange-gold individuals, but sex and exact variety cannot be confirmed from the images alone. Provide gentle flow, surface access, dense cover and calm tank mates for best results.
Honey Gourami (Colisa chuna) Care Guide

Easy - Moderate

Small freshwater labyrinth fish

The honey gourami is a small, peaceful labyrinth fish from the slow-moving waters of South Asia. Aquarium specimens may be natural honey-colored fish or selectively bred red and orange forms, like those shown here. The supplied images appear consistent with honey gourami, although sex cannot be confirmed reliably from the photographs. A planted aquarium with gentle flow, surface cover, stable warm water and calm tank mates suits this species well.
Blue Gourami (Trichogaster trichopterus) Care Guide

Easy - Moderate

Labyrinth fish; freshwater anabantoid

The blue gourami is a hardy labyrinth fish suited to a spacious, planted community aquarium. It is the blue color form of the three-spot gourami, a species that can become territorial, particularly when males mature or spawn. Provide gentle filtration, access to warm humid air above the water, hiding places, and a varied diet. The supplied images clearly show blue gouramis, although photographs alone cannot confirm sex or verify that every pictured fish belongs to the same color form.
Giraffe Perch (Nimbochromis venustus) Care Guide

Difficult

Lake Malawi predatory haplochromine cichlid

Nimbochromis venustus is a large predatory haplochromine cichlid from Lake Malawi, known in aquariums as the giraffe perch or giraffe cichlid. Juveniles are comparatively subdued, while adults develop blue facial tones and yellow, olive or gold body coloration with darker markings. The supplied listing describes two 4 cm fish as a pair, but sex cannot be confirmed reliably at that size. This species requires a spacious, rocky aquarium and carefully selected tank mates.
Dwarf Gourami (Trichogaster lalius)

Moderate

Small freshwater labyrinth fish

The dwarf gourami is a small labyrinth fish from vegetated, slow-moving waters of South Asia. Trichogaster lalius is generally peaceful, colorful and suitable for a planted community aquarium, although males can become territorial, especially around a bubble nest. A pair needs warm, stable water, gentle circulation, surface access and plenty of cover. The supplied identification is consistent with dwarf gourami, though color varieties and sex should be confirmed by physical examination.
Five-Bar Cichlid (Neolamprologus tretocephalus)

Difficult

Lake Tanganyika rock-dwelling cichlid

The five-bar cichlid, also called the five-striped cichlid, is a robust Lake Tanganyika predator with a dark blue-gray body marked by five broad black bars. Neolamprologus tretocephalus is territorial and can become highly aggressive, particularly when spawning. It suits experienced aquarists who can provide a spacious, rock-structured aquarium, alkaline hard water, and carefully selected tank mates. The supplied label identifies this fish as a pair, but sex and exact locality cannot be confirmed from the available information.
Gardner’s Splendid Carp (Fundulopanchax gardneri)

Moderate

West African killifish

Gardner’s splendid carp is a small West African killifish valued for its iridescent body, red markings and patterned fins. The supplied image appears to show a brightly colored male, while the source identifies a pair; exact locality form and sex of every fish cannot be confirmed from the available evidence. It is generally peaceful, though males may spar, and it is best kept in a covered, mature aquarium with gentle flow, subdued lighting and abundant plant cover.
Pelvicachromis taeniatus Nigeria Red

Moderate

West African dwarf cichlid

Pelvicachromis taeniatus, commonly known as the striped krib or taeniatus cichlid, is a small West African riverine cichlid valued for its parental behavior and locality-based color variation. “Nigeria Red” identifies a trade form or collection locality rather than a separate species. The supplied source label also calls these fish emerald perch, but that common name is not a standard scientific name. This species is generally manageable for experienced beginners when provided with stable, clean water, hiding places and a carefully planned community aquarium.
Apistogramma agassizii ‘Fire Red’

Moderate

South American dwarf cichlid

Apistogramma agassizii is a small South American cichlid valued for its intricate markings, elongated fins and interesting parental behavior. “Fire Red” is a selectively bred aquarium color form rather than a separate species. The supplied listing describes a pair, although sex, locality and breeding-line identity cannot be confirmed from the available material. This species suits a mature, planted aquarium with soft, clean water, subdued lighting, cover and a fine substrate.
Cockatoo Cichlid Orange (Apistogramma cacatuoides)

Easy - Moderate

South American dwarf cichlid

The Cockatoo Cichlid is a small South American dwarf cichlid known for its elongated dorsal fin, bold facial markings and colorful orange fin forms. Apistogramma cacatuoides comes from slow-moving waters and tributaries of the upper Amazon basin, where it shelters among leaf litter, roots and submerged vegetation. It is generally manageable for an aquarist who provides soft, clean water, caves and visual barriers. The supplied listing describes an orange pair, but sex and exact form should be confirmed by the seller because photographs alone are not definitive.
Dwarf Gourami Red (Trichogaster lalius)

Easy - Moderate

Asian labyrinth fish

The red dwarf gourami is a selectively bred color form of the dwarf gourami, a small labyrinth fish formerly widely known as Colisa lalia. It is suited to mature, planted community aquariums with gentle water movement and calm tank mates. Males can be territorial, especially when kept with females in confined conditions, so cover, visual barriers, and careful observation are important for a pair.
Cockatoo Cichlid Red (Apistogramma cacatuoides)

Moderate

South American dwarf cichlid

The Cockatoo Cichlid is a small South American dwarf cichlid valued for its personality, breeding behavior and colorful finnage. Apistogramma cacatuoides is generally adaptable when provided with clean, stable water, cover and a soft substrate. Males are larger and more vividly marked than females, while pairs become territorial around spawning sites. The supplied “red” designation most likely refers to a selectively bred color form; exact strain and sex confirmation cannot be established from the listing alone.
Discus (Symphysodon aequifasciatus) Care Guide

Difficult

South American freshwater cichlid

Symphysodon aequifasciatus is a large, laterally compressed cichlid from the Amazon Basin, valued for its calm behavior and striking disc-shaped body. It requires warm, clean, stable water and careful feeding, making it better suited to experienced aquarists. The supplied images show yellow, orange, red, white and dark color forms; cultivated strains can vary considerably, so exact variety identification from images alone is uncertain. Discus are social fish and generally thrive in groups rather than as isolated specimens.
Cape Lopez Killifish (Aphyosemion australe)

Moderate

West African non-annual killifish

The Cape Lopez killifish is a small, peaceful West African freshwater fish prized for its patterned body, flowing fins and manageable size. It inhabits slow-moving and temporary waters around coastal Gabon, including the Cape Lopez region. The supplied trade description identifies a pair as “Cape Lopez splendid carpets,” but this wording may describe a commercial strain rather than a formally recognized taxon. The image appears to show an orange form, so exact strain identification should be confirmed with the breeder or supplier.