Dwarf Galaxias,
Galaxiella spp., are small freshwater Fish from southern
Australia. The genus is split into two geographical groups which are
thought to have split between 28.3 and 34.3 million years ago, with
two species, Galaxiella nigrostriata and Galaxiella munda
found in southwestern Australia and a third, Galaxiella pusilla,
found in the southeast, where it occupies swamps, wetlands, shallow
lakes, billabongs, small creeks and artificial earthen drains on the
coastal plains of South Australia, Victoria and Tasmania. This
eastern species is listed as Vulnerable under the terms of both the
Australian Environment Protection and Biodiversity Conservation Act
and the International Union for the Conservation of Nature's Red Listof Threatened Species. It is also know to be highly diverse with
considerable habitat, genetic and morphological variation across its
range, leading to speculation that not all the Fish of this
population belong to the same species, in which case their
conservation status may need to be reviewed, as two or species with
lower populations and more restricted ranges would be at a higher
risk of being wiped out.
In a paper published in
the journal Zootaxa on 25 September 2015, Rhys Coleman of the
Victorian Centre for Aquatic Pollution Identification and Management
at the School of BioSciences at The University of Melbourne and the
Melbourne Water Corporation, Ary Hoffmann, also of the Victorian
Centre for Aquatic Pollution Identification and Management, and Tarmo
Raadik of the Arthur Rylah Institute for Environmental Research at
the Department of Environment, Land, Water and Planning and the
Department of Ichthyology at Museum Victoria publish the results of a
detailed morphological and genetic study of population of Galaxiella
pusilla from across its range,
and formally re-assign the western populations of the Fish to a new
species.
The
new species is named Galaxiella toourtkoourt,
which means 'little Fish in freshwater' in the Tjapwurrung, Korn
Kopan noot, and Peekwurrung language groups of Australia. The species
is smaller than Galaxiella pusilla,
or any other member of the
genus, and has a lower average number of vertebrae and dorsal fin
spines. Like all Dwarf Galaxies the new species is sexually
dimorphic, with larger females than males, in this case adult females
average 27-32 mm in length with the largest specimen found reaching
42 mm, and males average 25-28 mm with the largest specimen found
measuring 34 mm. The Fish are a pale olive-brown above with a silvery
underside and a reddish-pink patch around the gills. Adults have
three horizontal black stripes, though these tend to be fainter and
stippled in the females, particularly the upper two stripes, which
can be hard to discern. A horizontal red stripe runs between the
lower two black stripes in the males.
Galaxiella
toourtkoourt male (upper) and female (lower) from Narrow Neck
Drain, Hatherleigh, South Australia. Michael Hammer in Coleman et
al. (2015).
The
species is found in fresh or slightly brackish waters in still or
slow-moving waterways with plenty of shade, preferably with a clay or
silt bottom. The species seems relatively tolerant of variations in
temperature and water pH, but is only found at low elevations. It is
found in southeastern South Australia and southwestern Victoria.
Having a more restricted range than previously thought, as well as a
fragmented population threatened by habitat loss across much of its
range, it is recommended that Galaxiella toourtkoourt
be considered to be Threatened under the terms of the Australian
Environment Protection and Biodiversity Conservation Act and
Endangered under the terms of the International Union for the
Conservation of Nature's Red List of Threatened Species. Coleman also
recommend that the conservation status of Galaxiella
pusilla be raised to Threatened
and Endangered, for the same reasons.
Collection
sites and approximate current geographic distribution of Galaxiella
toourtkoourt (light grey) and
Galaxiella pusilla
(dark grey). Coleman et al. (2015).
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