Friday, September 25, 2015

A new freshwater smelt: Galaxiella toourtkoourt

The fish family Galaxiidae comprises about 40 species of small fish many of which are seriously threatened by introduced exotic salmonid species, particularly trout species, which as adults prey upon galaxiids and a juveniles compete with them for food.

Many galaxiid species live in fresh water for their entire life, but a good number is known to be amphidromous which means larvae are hatched in a river, but are washed downstream to the ocean, later returning to rivers as juveniles to complete their development to full adulthood. Most species of this group live in Southern Australia or New Zealand, but some are found in South Africa, southern South America, Lord Howe Island, New Caledonia, and the Falkland Islands.

The small genus Galaxiella contains three species that are only known to live in Australia. One of them, Galaxiella pusilla, is listed as ‘vulnerable’ in the IUCN Red List of Threatened Species. The very same species was already thought of consisting of two different species and this has now been confirmed and a new species, Galaxiella toourtkoourt, was described. This of course means that the threat for each of the two species might be even larger than it was determined while they were treated as one species.

The name of the new species is pronounced “Too-urt Koo-urt” (or Tu-urt Ku-urt), from the Australian indigenous language groups Tjapwurrung, Korn Kopan noot, and Peekwurrung, meaning ‘little fish in freshwater’. 

For the experts: The dwarf galaxias, Galaxiella pusilla (Mack), is a small, threatened freshwater fish from coastal south-eastern Australia. Recent genetic studies, using multiple nuclear and mitochondrial DNA markers, found substantial differences between populations in western Victoria and south Australia (‘west region’) compared to eastern Victoria, Flinders Island, and Tasmania (‘east region’) that suggest the presence of a cryptic species. Morphological measurements and meristic counts from multiple populations within each region were undertaken to investigate potential differences between regions. Several characters, found to discriminate between individuals in the regions and to be diagnostic for two taxa, were used to describe a new species, Galaxiella toourtkoourt, for the west region. This is only the second species in the Galaxiidae to exhibit sexual dimorphism. The original description of Galaxiella pusilla, based on five specimens, is revised following examination of a large number of individuals. Both species are considered nationally threatened and are categorised as ‘endangered’; the revised distribution of G. pusilla s.s. is reduced by approximately 60%. A number of inconsistencies in the most recent revision of the genus Galaxiella are also corrected.

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