Pseudomugil signifer KNER, 1866

Pacific Blue-eye

SynonymsTop ↑

Atherina signata Günther, 1867; Pseudomugil signata (Günther, 1867); Atherinosoma jamesonii Macleay, 1884

Etymology

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

signifer: from the Latin signifer, meaning ‘bearing signs’.

Classification

Order: Atheriniformes Family: Pseudomugilidae

Distribution

The type series was collected in the vicinity of Sydney, New South Wales state, eastern Australia, and following current knowledge P. signifer is the most widely-distributed blue-eye in Australia.

Its range extends along the majority of the country’s eastern coastline, southwards from the Cape York Peninsula in northern Queensland state to Merimbula Lake in southern New South Wales, near the border with Victoria state.

There exist populations on some offshore islands, including those in the Torres Strait, while it’s also known from the western side of the Cape York Peninsula in the Embley and Mission river systems.

It’s remarkably variable throughout its range with numerous populations exhibiting localised differences in colour pattern, body size, and fin morphology.

Those from northern and southern localities have been considered distinct by various authors, for example, and in Queensland forms originating north and south of the Herbert River also appear dissimilar, with an intermediate form apparently native to the area around Townsville (Ross River).

Habitat

Generally found within 15-20 km of the sea but habitat-type is extremely variable. It’s been recorded in full marine conditions as well as pure freshwater environments, and commonly inhabits coastal mangrove creeks, swamps, and salt marshes.

Freshwater habitats tend to comprise lowland swamps or forest streams with clear water but some populations inhabit acidic, tannin-stained, black waters.

It’s also abundant in the artificial canals typical of residential zones in the Gold Coast, southern Queensland.

Water temperatures vary between 15 – 28 °C, although lower values are applicable only to southern populations during winter. PH has been measured to range between 5.5 – 7.8 depending on locality.

Maximum Standard Length

35 – 70 mm. Varies depending on origin, with northern populations often growing considerably larger than those from southern localities.

Aquarium SizeTop ↑

An aquarium with base dimensions of 60 ∗ 30 cm or equivalent should be the minimum considered in most cases, though some of the more diminutive forms may be maintained in smaller surroundings, while the largest northern forms might require something substantially bigger (see ‘Behaviour and Compatability’).

Maintenance

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.

Despite it’s euryhaline nature the use of marine salt is unnecessary with specimens collected from brackish or marine habitats able to survive and breed in pure freshwater, and vice versa.

Water Conditions

Temperature: 20 – 26 °C

pH: 6.5 – 7.5

Hardness: 90 – 268 ppm

Diet

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 Daphnia, Moina, Artemia nauplii, micro worm, etc., although small/crushed floating dried foods are also accepted.

Behaviour and CompatibilityTop ↑

Most forms are 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.

P. signifer is a shoaling species and should be kept in a group of at least 8-10 specimens, ideally more. 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.

Mature males of the larger-growing northern populations are very intolerant of one another when in spawning condition and subdominant individuals may be killed in smaller aquaria.

These should be maintained in spacious surroundings alongside other pelagic fishes such as Melanotaenia spp. in order to disperse aggression.

Sexual Dimorphism

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

Males of certain populations develop long, filamentous tips to the dorsal and anal-fins but these are usually lost upon capture and apparently never appear in captive fish.

Reproduction

This species is an egg-scatterer exhibiting no parental care and will often consume its own eggs and fry given the opportunity, although in a well-decorated aquarium some may survive.

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 by adhesive filaments.

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

In nature it displays a seasonal reproductive cycle coinciding with the onset of the wet season, around October-December, when food and aquatic vegetation are at their most plentiful.

Spawning occurs during daylight hours with a peak of activity in late morning/early afternoon when water temperature is 24-28 °C, and in the aquarium breeding can occur throughout the year if temperature is raised to these values.

There exist two basic methods. 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 10-21 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.

NotesTop ↑

Wild populations from Low Island, Cape York, and the Bremer River, all in Queensland, were described as P. signatus affinis (Whitley 1935), Atherinosoma jamesonii (Macleay 1884), and Atherina signata (Günther 1867), respectively.

Following a name change the latter was applied to northern populations (see ‘Distribution’) which were referred to as Pseudomugil signatus for a number of years but all three names have been considered synonyms of P. signifer since the publication of genetic research in 1979 in which 14 separate populations could not be distinguished from one another.

However, recent unpublished analyses apparently suggest otherwise, and the species may yet be split into two or more distinct taxa. Moreover, wild fish from the northern and southern ends of its range would not hybridise in captive experiments.

The family Pseudomugilidae was erected by Saeed et al. (1989) and 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 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.

References

1. Allen, G. R., 1980 - Records of the Western Australian Museum 8(3): 449-490
   A Generic Classification of The Rainbowfishes (Family Melanotaeniidae).
2. Allen, G. R., H. Midgley, and M. Allen, 2002 - Western Australian Museum: i-xiv + 1-394
   Field guide to the freshwater fishes of Australia.
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.
6. Wong, B. B. M., S. Keogh, and D. J. McGlashan, 2004 - Molecular Ecology 13: 391-401
   Current and historical patterns of draiange connectivity in eastern Australia inferred from population genetic structuring in a widespread freshwater fish Pseudomugil signifer (Pseudomugilidae).