Melanotaenia sahulensis (Skull Creek) - image© Gunther Schmida

Melanotaenia sahulensis

Species Summary
Melanotaenia sahulensis are generally silver-white to grey-brown on the upper half of body, lower half of body white; seven or eight black body stripes, intensity typically increasing to full and bold as adults; head brownish grey, lips greyish sometimes with hint of yellow or orange; small red to orange mark on the upper operculum; iris silver; fins colourful, with distinct zonation in the dorsal and anal fins formed by a thick submarginal dark grey to black band; a thin area of colour above the band on the fin margins (white through orange, sometimes red) and below the black band typically an area of yellow to orange. Colour intensifies in breeding males with more prominent body stripes and bright fin coloration; sexual dimorphism is obvious. A faint and sometimes brighter pale yellow to orange nape stripe can be 'flashed' by courting males or to a lesser degree by sparring males. Most easily separated from other Australian members of the maccullochi species group based on silver-grey body colour, bold and full body stripes as adults and tri-tone dorsal and anal fins.

Melanotaenia sahulensis (Papua New Guinea) - image© Neil Armstrong

There appears to be regional variation in fin colour of this species, with the margin of the dorsal and anal fins, and to a lesser degree caudal and pelvic fins, ranging from white (e.g. Moa Island, Sigabaduru), through white-orange (e.g. Skull Creek) to red (western Papua New Guinea) - this last colour form was first observed in captive fish in Australia in the 1990s and likely originated from the Bensbach or Morehead rivers' where fish are known to have been collected and imported. The form with red fin margins could lead to confusion with M. maccullochi. However, the thick marginal band creating fin colour zones, black body stripes and silver grey base body colour allow ready identification.

Melanotaenia sahulensis (Jardine River) - image© Neil Armstrong

Distribution & Habitat
Melanotaenia sahulensis is native to northeast Cape York Peninsula, Australia and southern central New Guinea. Locations include the northern tip and east coast of Cape York from the Jardine River, Bamaga area, Shelburne Bay area and around as far south as Scrubby Creek; Torres Strait (Moa Island). In New Guinea they are from the Pahoturi River to the Bensbach river systems including the mid-Fly; and from the Merauke area. This patchy distribution comprises a broad range with regional habitat variation, but includes larger lateral floodplain systems and small swampy creeks including dune lakes, with dense cover. Cape York habitat generally consists of small streams and Pandanus swamps in sand-soil country. During non-flood periods the water is typically clear with ample cover in the form of either log debris or aquatic vegetation. The species also occurs in lily lagoons and is most frequently found in acid waters (pH 5.5-7.0). Information specific to this species has been merged and confused with M. maccullochi and to a lesser degree M. wilsoni.

Melanotaenia sahulensis (Moa Island) - image© Gunther Schmida

Literature
Hammer M.P., G.R. Allen, K.C. Martin, M. Adams and P.J. Unmack (2019) Two new species of dwarf rainbowfishes (Atheriniformes: Melanotaeniidae) from northern Australia and southern New Guinea. Zootaxa 4701 (3): 201-234.

Adrian R. Tappin
December, 2019