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Pseudomugil furcatus NICHOLS, 1955

Forktail Blue-eye

SynonymsTop ↑

Popondetta furcata (Nichols, 1955); Popondichthys furcatus (Nichols, 1955); Pseudomugil furcata Nichols, 1955


Pseudomugil: from the Ancient Greek ψευδής (pseudes), meaning ‘false, lying, untrue’, used here as a prefix, and the generic name Mugil.

furcatus: from the Latin furcatus, meaning ‘forked’, in reference to the shape of the caudal-fin in this species.


Order: Atheriniformes Family: Pseudomugilidae


Described from ‘Peria Creek, Kwagira River, eastern Papua New Guinea’ and despite its popularity in the aquarium hobby is endemic to a relatively small area in the country’s Northern and Milne Bay provinces.

It’s been recorded in the Musa and Kwagila river basins which drain into Dyke Ackland Bay and Collingwood Bay, respectively, and presumably occurs in drainages between the two as well.

Wild specimens are not available in the aquarium trade with all those in the hobby bred on a commercial basis and apparently originating from a single collection in 1981.


Primarily inhabits low altitude, heavily-vegetated forest streams with slow to moderate current and clear water.

Air temperatures in Papua New Guinea are quite stable although rainfall increases dramatically during the northwest monsoon between December and March, this typically bringing about a rise in turbidity, volume, and flow rate of rivers and streams.

Conversely, during the dry season such habitats may become partially dried, and the type specimens were collected from pools in ‘intermittent’ streams alongside Tateurndina ocellicauda.

In 1981 the water temperature was measured at 75.2 – 83.3 °F/24 – 28.5 °C, pH 7.0 – 8.0, and hardness 90 – 180 ppm.

Maximum Standard Length

40 – 60 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 60 ∗ 30 cm should be the smallest considered.


Best kept in a densely-planted tank and an excellent choice for the carefully-aquascaped set-up.

The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tank also seems to be appreciated and adds a more natural feel.

If you wish to raise fry alongside the adults the addition of fine-leaved aquatic moss such as a Taxiphylum sp. is advisable (see ‘Reproduction’).

The water should be well-oxygenated and a degree of flow is advisable.

Do not add this fish to a biologically immature aquarium as it can be susceptible to swings in water chemistry.

Water Conditions

Temperature: The air and water temperatures in its natural habitats do not vary a great deal and in aquaria the fish tend to fare poorly unless maintained within the range 24 – 28 °C.

pH7.0 – 8.0

Hardness268 – 536 ppm


Feeds chiefly on floating or suspended zooplankton, phytoplankton, and invertebrates in nature, and in the aquarium must be offered items of a suitable size.

Ideally much of the diet should comprise live foods such as DaphniaMoinaArtemia nauplii, micro worm, etc., although small/crushed floating dried foods are also accepted.

Behaviour and CompatibilityTop ↑

Peaceful and suitable for well-chosen community aquaria alongside fishes of comparable size, disposition, and requirements with many cyprinids, gobiids, eleotrids, and smaller melanotaeniids suitable.

The eleotrid Tateurndina ocellicauda, with which it occurs in nature, is particularly appropriate.

P. furcatus is a shoaling species and should be kept in a group of at least 8-10 specimens.

Maintaining it in such numbers will not only make the fish less nervous but result in a more effective, natural-looking display.

Males will also display their best colours and some fascinating behaviour as they compete with one other for female attention.

Sexual Dimorphism

Males are more highly-patterned and colourful than females and the unpaired fins become noticeably extended as they mature.


This species is an egg-scatterer exhibiting no parental care and will consume its own eggs and fry given the opportunity.

Since all aquarium fish appear to derive from a single collection (see ‘Distribution’) there are also some inbreeding issues which can include reduced fertility, life span, and a high rate of deformity in fry.

Spawning is more likely in temperatures towards the upper end of the range suggested above, with females capable of depositing a few eggs daily for a period of several days, these being attached to aquatic vegetation or other substrate.

An individual male may also mate with multiple females during a single day, and spawning usually continues throughout daylight hours during warmer periods.

There exist two basic methods for aquarium breeding.

The first involves isolating a small group of 6-8 individuals or single male and two or three females into a container with an air-powered sponge filter and spawning medium in the form of nylon mops or aquatic moss.

The medium is checked on a daily basis and any eggs removed to a separate container for incubation and hatching.

The alternative is to maintain a colony of adults in a larger, fully-decorated set-up which if well-planted should allow some fry to survive.

Since the latter spend the early part of life close to the water surface aquatic mosses from the genus Taxiphylum attached to décor high in the water column apparently produce the most favourable results, but floating plants with trailing roots are also recommended.

The latter approach is normally less productive but simpler and more reliable as mature, planted aquaria facilitate relatively stable water conditions and the resident microfauna can constitute a valuable early food source for fish fry.

The incubation period is around 21 days depending on temperature and the fry are able to accept Artemia nauplii, micro worm, and similarly-sized foods immediately.

They can also be raised using good quality, powdered dry products of which some are available in incrementally-graded particle sizes.

Should eggs containing developed embryos fail to hatch they can apparently be stimulated to do so by putting them in a small vial or similar container with some water from the aquarium and shaking it vigorously, or placing it in your pocket and walking around with it. It appears the resultant change in pressure causes the eggs to hatch.

Small meals should be offered at least twice daily. Aged water can result in high mortality so regular, small water changes are essential and uneaten food should not be allowed to accumulate in the rearing tank.

Pseudomugil spp. are quite short-lived with females tending to survive for only a single reproductive season in nature.

Though lifespan tends to increase in well-maintained aquaria the fish will normally be less fecund once they reach an age of 12-18 months.

Until the age of approximately 8 months any eggs produced by females tend to be under-sized and infertile or simply fail to develop, but even when deposited by fully-mature adults more than 50 % are often infertile.

Given that this species produces relatively few, large eggs this can prove a real challenge for breeders.

Thanks to Mike Vulis.

NotesTop ↑

This species is also traded as ‘forktail rainbowfish’ or ‘yellow forktail’, and it’s also undergone several changes in scientific name since description.

Pseudomugil furcatus is the original designation, but Allen (1980) created the genus Popondetta for it on the basis of morphological characters including number of anal-fin rays (16-20 in P. furcatus, 8-12 in other Pseudomugil spp.), absence of anterior projections at ventral midline of pelvic girdle (vs. presence), and absence of distinct scale radii (vs. presence).

Popondetta connieae (Allen, 1981) was described the following year but the generic name was later found to have been erected for a species of beetle in 1978, with this earlier usage taking precedence.

The alternative Popondichthys (Allen, 1987) was thus raised for P. connieae and P. furcatus but remained valid for just two years with Saeed et al. (1989) considering them (once again in the case of P. furcatus) members of Pseudomugil.

The latter authors also erected the family Pseudomugilidae, a grouping which currently comprises the genera Kiunga, Pseudomugil, and Scaturiginichthys.

Members are related to rainbowfishes of the family Melanotaeniidae but differ in lacking a mesethmoid, possessing an infraorbital series with only the anterior member present (the kachrymal), and with an articular bone as high as the dentary bone.

The family Telmatherinidae is also a close relative, with Sparks and Smith (2004) recommending that all telmatherinid genera be included in Pseudomugilidae based on the results of their phylogenetic analysis, in which Marosatherina ladigesi was nested within Pseudomugilidae, these together comprising the sister group to Melanotaeniidae.

Herder et al. (2006) suggested that since M. ladigesi was the only telmatherinid included in the investigation, meaning that data for 94% of member species plus DNA of some important comparative taxa was not analysed,  any such conclusions should be withheld pending additional study.

The Pseudomugilidae and Telmatherinidae do appear to represent a single clade, however, and this forms a sister group to another clade formed by the Australian and New Guinean Melanotaeniidae plus the Malagasy Bedotiidae, which may seem surprising given their respective modern-day distributional patterns.

The precise origin and subsequent dispersal of the latter two has therefore been the subject of debate, with some palentologists suggesting that Madagascar’s freshwater fishes derived from a trans-oceanic dispersal during the Cenozoic Era, but the most compelling recent arguments indicate a freshwater radiation which occurred during the Mezozoic break-up of Gondwana.


  1. Nichols, J. T., 1955 - American Museum Novitates 1735: 1-6
    Results of the Archbold expeditions. No. 71. Two new fresh-water fishes from New Guinea.
  2. Allen, G. R., 1980 - Records of the Western Australian Museum 8(3): 449-490
    A Generic Classification of The Rainbowfishes (Family Melanotaeniidae).
  3. Herder, F., J. Schwarzer, J. Pfaender, R. K. Hadiaty, and U. K. Schliewen, 2006 - Verhandlungen der Gesellschaft für Ichthyologie Band 5: 139-163
    Preliminary checklist of sailfin silversides (Teleostei: Telmatherinidae) in the Malili Lakes of Sulawesi (Indonesia), with a synopsis of systematics and threats.
  4. Sparks, J. S. and W. L. Smith, 2004 - Molecular Phylogenetics and Evolution 33(3): 719-734
    Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teleostei: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater.
  5. Tappin, A. R., 2010 - Art Publications: 1-484
    Rainbowfishes - Their Care and Keeping in Captivity.

13 Responses to “Pseudomugil furcatus – Forktail Blue-eye (Popondetta furcata, Popondichthys furcatus)”

  • mikev

    More problems for you:

    Length should be increased to at least 6cm (for males). This is what Tappin says.. albeit I’m pretty sure that my 3 yo specimen are close to 7cm.

    “originating from a single collection in 1981” — append perhaps: the inbreeding manifests itself in reduced fertility, reduced life span, and high deformity rate.

    (Details on fertility if you want them: until about 8 months of age, most of the produced eggs are about half of the normal size, and naturally most are infertile or fail to develop. But even when the eggs become normal size, fertility is under 50%, sometimes well under. Given that the eggs are large and few, this is a real problem. In comparison, p.pellucidus produce eggs which are even larger… but even small initial eggs develop properly and the fertility is near 100%. Of course, p.pellucidus was collected only a couple of years ago).

    “The family Telmatherinidae is also a relative” (in all profiles) perhaps better to say “is a closer relative” (confirmed by the latest DNA work).

  • All done, cheers Mike!

  • mikev

    Very welcome. There will be some more after rereading them, but here is one general thing to notice: currently all profiles say

    Should eggs containing developed embryos fail to hatch they can apparently be stimulated to do so by putting them in a small vial or similar container with some water from the aquarium and shaking it vigorously, or placing it in your pocket and walking around with it. It appears the resultant change in pressure causes the eggs to hatch.
    This is kind of true…but again, the problem is not uniform for all species. Some are relatively prone to this (ivantsoffi, reticulatis, less but still red neons — incidentally all three are closely related), but most of the others (gerts, sigs) never IME have this issue…

    And with reticulatis the problem is really severe, at least for me: so far I had three fertile eggs from them, and could not force-hatch any of them with the techniques described above or my preferred way of stirring the container cup with a teaspoon…

    And with ivansoffi where force-hatching may indeed be needed, it is not the worst problem: it may also happen that a fry hatches but remains stuck in the shell… the solution is to separate the too with toothpicks… only someone with perfect vision or steady hands can do this.

    I’m actually not suggesting changing anything in the profile now, only ranting that to me this part seems iffy…

  • ridwan

    I have an albino pseudomugil furcatus.

  • mikev

    Post a photo please, this is very interesting!

  • ridwan

    How to posting photo in here, mikev? I just using tablet not computer.
    Give me your email adresse, i send the photos to your email. And after that, you can posting the photos in here, mikev.

  • mikev

    Thank you very much, it is gorgeous! Very envious!

    You can post photos anywhere and just provide a link… there is no way asaik to embed photos or attach them in the Comments area. You may be able to attach photos to posts in the regular forum.

    Matt, please delete my email when you have a chance.

    Ridwan’s photos are here:

  • Removed as requested Mike. Also agree this is very interesting! Are you breeding them in numbers Ridwan, and would it be possible to add your photos to the profile page here?

  • ridwan

    Sorry, matt, i still cannot add the photos in here.
    Yes, for now i have 15 fishes albino furcatus. And over 50 Fishes childrens albino furcatus.

  • That’s fine, I got the pics via Mike’s links above and was asking if I can add them to the main profile images on the right. Is it ok?

  • ridwan

    Maybe i can posting in SF pages in facebook.

  • ridwan

    Yes, thats oke, matt.

  • lizz

    Can these fish school with black neon tetras, can they live with bettas?

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