Pseudomugil inconspicuus (Darwin) - photo© Gunther Schmida
Pseudomugil inconspicuus is a small slender-bodied species, usually not exceeding 35 mm in length. They have two dorsal fins, very close together, the first much smaller than the second. The body colouration is translucent bluish with some scattered melanophores and clear to slightly yellowish fins. A uniformly thin, uninterrupted, longitudinal line of black pigment extends from just above the origin of the first pectoral fin ray to the base of the caudal fin. This line is enhanced with metallic blue reflective scales above and below. Pseudomugil inconspicuus show only slight sexual dimorphism involving the dorsal and anal fins only. Mature males have a slightly larger first dorsal fin than females (sometimes with a short filamentous extension). The second dorsal fin often has a short filamentous extension as well. Pseudomugil inconspicuus does not seem particularly closely related to any other described Pseudomugil. They were scientifically described by Tyson R. Roberts in 1978 from specimens collected from the mouth of the Fly River, Papua New Guinea in 1975.
Distribution & Habitat
Pseudomugil inconspicuus are probably widely distributed in estuarine and coastal freshwater habitats across northern Australia and southern New Guinea, but have escaped notice due to their small size and largely inaccessible habitats. They are known from several locations in New Guinea and probably extend from the Kikori River to the Vogelkop Peninsula. They have been collected in the Fly River, Bintuni Bay, Timika region and Bristow Island, near Daru Island. In Australia they have been found in scattered localities around Darwin and Kakadu regions in the Northern Territory. They have also been collected from Andoon Creek (Mission River) on the west-coast of Cape York Peninsula and Jacky-Jacky Creek on the east-coast of Cape York Peninsula in Queensland.
Pseudomugil inconspicuus are euryhaline and tolerate a wide range of ecological conditions. Although more commonly found in small brackish estuarine creeks, they also inhabit pure freshwater habitats, especially during the wet season. During the wet season, freshwater flowing into these habitats dilutes the waters to fresh. Water thus varies from saline through brackish to fresh. However, habitat preference appears to be mangrove-lined muddy brackish creeks, where they are commonly found in large numbers. They have been found in hypersaline waters (28-40 ppt) and at temperatures of 22-39°C. They have been observed sheltering among submerged roots or inundated leaves and branches, often in muddy waters. They are frequently seen swimming in midwater rather than near the surface. They are sympatric with Pseudomugil cyanodorsalis over part of their range.
Pseudomugil inconspicuus are currently rare in the aquarium hobby and as far as I know, there are no published reports of them having been bred in captivity. So far, they have proved rather delicate when being collected and difficult to maintain in captivity. Captured specimens carry high parasite loads and seem to waste away slowly. In their natural environment spawning usually commences during the early-wet season from October to January. They are a planktivorous species and adapt well to freshwater environments.
Allen G.R. (1980) A Generic Classification of the Rainbowfishes (Family Melanotaeniidae). Records of the Western Australian Museum 8 (3): 449-490.
Allen G.R. (1989) Freshwater fishes of Australia. T.F.H. Publications, Inc., Neptune City, New Jersey.
Allen G.R. (1991) Field guide to the freshwater fishes of New Guinea. Christensen Research Institute, Madang, Papua New Guinea.
Allen G.R., S.H. Midgley and M. Allen (2002) Field guide to the freshwater fishes of Australia. Western Australian Museum.
Roberts T.R. (1978) An ichthyological survey of the Fly River in Papua New Guinea with descriptions of new species. Smithsonian Contributions to Zoology No. 281: 1-72.
Saeed B., W. Ivantsoff, and G. R. Allen (1989) Taxonomic revision of the family Pseudomugilidae (Order Atheriniformes). Australian Journal of Marine and Freshwater Research 40: 719-787.
Adrian R. Tappin
Updated July, 2016