The forktail blue eye (Pseudomugil furcatus) is a small forktail blue eye rainbowfish from eastern Papua New Guinea, named for its deeply forked yellow tail and electric-blue eyes.
Despite its popularity it has a small natural range in the Northern and Milne Bay provinces, where it has been recorded in the Musa and Kwagila river basins.[2] There it lives in clear, slow to moderately flowing forest streams with dense vegetation. The type specimens came from pools in seasonal streams, collected alongside the peacock gudgeon.[2] Wild fish are not traded. Seriously Fish reports that every captive fish appears to descend from a single 1981 collection.[2]
Blue eyes are often lumped together as "blue eye rainbowfish", but the group includes very different fish. This guide covers forktail care and breeding, then compares it with the spotted, Pacific and red neon blue eyes that searches also turn up.
Forktail Blue Eye Tank Setup
A tank with a base of 60 × 30 cm (24 × 12 in), around 55 litres, is the smallest Seriously Fish considers suitable.[2] This species shows its best colour in a densely planted, carefully scaped tank, with floating plants and driftwood branches to soften the light.[2] Keep the water well oxygenated with some gentle flow.[2] Fine-leaved moss placed high in the tank gives fry a refuge if you want some to survive in the display tank.
Forktail Blue Eye Water Parameters
This species does poorly outside a narrow temperature band. Keep it at 24–28 °C (75–82 °F) in hard, alkaline water of pH 7.0–8.0 and 15–30 dGH.[2] Measurements taken at the type locality in 1981 gave 24–28.5 °C and pH 7.0–8.0, which supports those figures.[2] FishBase lists a cooler 24–26 °C with softer water, but captive lines bred in hard water are the ones on sale.[1]
Stability matters more than any single number. Seriously Fish warns against adding the species to a biologically immature tank, because it is susceptible to swings in water chemistry.[2] Wait until the tank has tested stable for several weeks.
Feeding
In the wild, forktails feed on floating and suspended zooplankton, phytoplankton and small invertebrates.[2] In the aquarium, much of the diet should be small live foods such as Daphnia, Moina, brine shrimp nauplii and microworms. Small or crushed floating dry foods are also accepted.[2] These are surface and midwater feeders, so sinking pellets do little for them.
Tank Mates and Group Size
This is a peaceful shoaling fish. Keep at least eight to ten, which makes the fish less nervous and brings out the males' best colours and display behaviour.[2] Good companions are fish of similar size and temperament that suit hard water: small rasboras and other cyprinids, small gobies, smaller rainbowfish, and especially the peacock gudgeon (Tateurndina ocellicauda), which shares its home streams.[2]
Breeding Forktail Blue Eyes
Males are more boldly patterned and colourful, and their unpaired fins lengthen as they mature.[2] The species scatters its eggs and gives no parental care, and adults eat both eggs and fry.[2]
- Spawning is most likely towards the warm end of the range. Females lay a few eggs each day over several days, attaching them to plants or spawning mops.[2]
- Either keep a breeding group with a sponge filter and mops, collecting eggs daily, or let fry grow up among moss in a mature planted tank.[2]
- Eggs take around 21 days to hatch, depending on temperature. Fry can eat brine shrimp nauplii and microworms right away.[2]
- Feed small meals at least twice a day, and change water little and often. Aged water causes high fry losses.[2]
Expect low numbers. Females under about eight months old tend to lay small, infertile eggs, more than half of eggs from mature adults are often infertile, and fertility falls after 12–18 months.[2] The single-collection origin of captive stock is linked to reduced fertility, shorter lifespan and a high rate of deformity in fry.[2]
Forktail Blue Eye vs Other Blue Eye Rainbowfish
"Blue eye" refers to the genus Pseudomugil, small relatives of the rainbowfishes. In 1989 Saeed and colleagues returned the forktail to Pseudomugil after a brief period in the genera Popondetta and Popondichthys, and placed it in the family Pseudomugilidae.[2] The common aquarium species differ in ways that affect care:
| Species | Size | Origin | Water |
|---|---|---|---|
| Forktail, P. furcatus | ≈5 cm | Eastern Papua New Guinea[1] | Hard, alkaline, 75–82 °F[2] |
| Spotted blue eye, P. gertrudae | 3.8 cm SL | Northern Australia, PNG, Aru Islands[3] | Soft to medium, pH 4.5–7.5[3] |
| Pacific blue eye, P. signifer | Up to 7 cm SL | Eastern Australian coast[4] | Fresh to fully marine habitats; 68–79 °F[4] |
| Red neon blue eye, P. luminatus | 1.9 cm SL | Papua province, Indonesia[5] | IUCN Endangered (2019)[5] |
The spotted blue eye is covered on our gertrudae rainbowfish page. Do not keep different blue eye species together if you plan to breed them, and check that the water hardness suits whichever species you choose.
Forktail Blue Eye FAQ
Is the forktail blue eye a rainbowfish?
How many should I keep in a group?
How long do forktails live?
What is a red neon blue eye?
Related Species
References
- Froese, R. & Pauly, D. (eds.). Pseudomugil furcatus Nichols, 1955. FishBase, version 2025. fishbase.se
- Seriously Fish. Pseudomugil furcatus (Forktail Blue-eye). Species profile. seriouslyfish.com
- Seriously Fish. Pseudomugil gertrudae (Spotted Blue-eye). Species profile. seriouslyfish.com
- Seriously Fish. Pseudomugil signifer (Pacific Blue-eye). Species profile. seriouslyfish.com
- Froese, R. & Pauly, D. (eds.). Pseudomugil luminatus Allen, Unmack & Hadiaty, 2016. FishBase, version 2025. fishbase.se