Pseudomugil cyanodorsalis
Neon Blue-eye
Etymology
Pseudomugil: from the Ancient Greek ψευδής (pseudes), meaning ‘false, lying, untrue’, used here as a prefix, and the generic name Mugil.
cyanodorsalis: from the Ancient Greek κυανός (kýanos), meaning ‘dark blue’, and Latin dorsalis, meaning ‘of or pertaining to the back’, in reference to the colour of the upper body in this species.
Classification
Order: Atheriniformes Family: Pseudomugilidae
Distribution
Type locality is ‘Crab Creek, about 15 kilometers east of Broome, Western Australia, about 17°59’S, 122°23’E’, but this species appears to be widely-distributed in coastal waters of northern Australia and possibly southern New Guinea.
When present it tends to be locally abundant and occur in large aggregations.
In Western Australia it’s been recorded from close to Broome and Wyndham, in the Northern Territory around Darwin, the Mary River National Park and on Melville Island, and in Queensland the Norman River.
Populations are normally labelled as such by enthusiasts in order to avoid cross-breeding.
Habitat
Euryhaline and thus capable of withstanding significant fluctuations in salinity and other water conditions.
It’s been recorded in full marine conditions as well as pure freshwater environments, and commonly inhabits coastal mangrove creeks and swamps.
Such changes may occur on a daily or seasonal basis depending on locality, with some habitats influenced by daily tides whereas others become hypersaline during the dry season before being filled with fresh water when the rains return, for example.
Aquatic plants aren’t usually present with substrates tending to be composed of silt and mud, but cover in the form of marginal vegetation or tangles of submerged mangrove roots is common.
At some localities it can be found living sympatrically alongside its congener P. inconspicuus.
When the type series was collected the water temperature at Crab Creek was 71.6°F/ 22°C with a specific gravity of 1.030, i.e., the salinity was greater than that of seawater.
Maximum Standard Length
30 – 35 mm.
Aquarium SizeTop ↑
An aquarium with base dimensions of 45 ∗ 30 cm or equivalent should be the smallest considered.
Maintenance
Opinions vary as to whether this species requires salt or not, though the general consensus is that it’s more vigorous, fecund, and long-lived when maintained in brackish conditions.
The precise specific gravity is not critical given the adaptability of the fish, but a value between 1.001 and 1.010 is normally recommended.
Other hobbyists use more simple measurements such as adding 1 tsp of marine salt per 10 l of aquarium water, for example.
Additional décor is largely down to personal taste and purpose of the set-up. The majority of live plants are unlikely to survive in brackish water though àrtificial alternatives can certainly be used.
Thin branches can be used to simulate the mangrove roots with which the fish are often associated in nature while rocks and larger pieces of driftwood can be added as you wish.
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, and be sure to use a cover as it does jump at times.
Water Conditions
Temperature: 21 – 31 °C
pH: 7.0 – 8.5; will not do well in acidic water.
Hardness: 179 – 447 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 ↑
Peaceful but unsuitable for the general community aquarium since it’s easily outcompeted and quite timid.
It’s best maintained alone or alongside fishes of comparable size, disposition, and requirements though the choice is somewhat limited if the fish are being maintained in brackish conditions.
P. cyanodorsalis 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.
Sexual Dimorphism
Males are more highly-patterned, colourful, and larger than females and the unpaired fins become noticeably extended as they mature.
Reproduction
This species is an egg-scatterer exhibiting no parental care and will consume its own eggs and fry given the opportunity.
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 laid directly onto the substrate.
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 but in the aquarium can occur throughout the year if warm temperatures are maintained.
There exist two basic methods of 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.
If using this method it can also pay dividends to carefully syphon the gravel when collecting eggs as if a substrate is present this species often shows a preference for depositing them there.
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 they 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 aquaria facilitate relatively stable water conditions and the resident microfauna can constitute a valuable early food source for fish fry.
The incubation period is 14-21 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 ↑
P. cyanodorsalis can easily be told apart from other members of the genus since males possess a unique colour pattern with the upper portion of the body a bright metallic blue.
It’s also known as the ‘blueback blue-eye’ in reference to this character.
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
- Allen, G. R., 1980 - Records of the Western Australian Museum 8(3): 449-490
A Generic Classification of The Rainbowfishes (Family Melanotaeniidae). - Allen, G. R. and N. Sarti, 1983 - Revue française d'Aquariologie Herpétologie 10(2): 47-50
Pseudomugil cyanodorsalis, une nouvelle espèce de blue-eye (Melanotaeniidae) d'Australie nord-occidentale. - Allen, G. R., H. Midgley, and M. Allen, 2002 - Western Australian Museum: i-xiv + 1-394
Field guide to the freshwater fishes of Australia. - 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. - 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. - Tappin, A. R., 2010 - Art Publications: 1-484
Rainbowfishes - Their Care and Keeping in Captivity.
