Galaxiidae


The Galaxiidae are a family of mostly small freshwater fish in the Southern Hemisphere. The majority 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. One galaxiid species, the common galaxias, is probably the most widely naturally distributed freshwater fish in the Southern Hemisphere. They are coolwater species, found in temperate latitudes, with only one species known from subtropical habitats. Many specialise in living in cold, high-altitude upland rivers, streams, and lakes.
Some galaxiids live in fresh water all their lives, but many have a partially marine lifecycle. In these cases, 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. This pattern differs from that of salmon, which only return to fresh water to breed, and is described as amphidromous.
Freshwater galaxiid species are gravely threatened by exotic salmonid species, particularly trout species, which prey upon galaxiids and compete with them for food. Exotic salmonids have been recklessly introduced to many different land masses, with no thought as to impacts on native fish, or attempts to preserve salmonid-free habitats for them. Numerous localised extinctions of galaxiid species have been caused by the introduction of exotic salmonids, and a number of freshwater galaxiid species are threatened with overall extinction by exotic salmonids.

Evolution

Phylogenetic evidence alternatively places galaxiids within the Protacanthopterygii, or more recently as the sister group to the Neoteleostei. Their ancestors are thought to have diverged from the neoteleosts around the Triassic-Jurassic boundary.
The earliest definitive fossils of galaxiids are from the Miocene of New Zealand, which can be placed in the extant genus Galaxias. This young fossil range contrasts with the presumed ancient origins of the group. In 1998, a possible Late Cretaceous galaxiid from South Africa was described as Stompooria. However, later studies have questioned this assignment, as Stompooria differs from galaxiids in many morphological traits, especially in the presence of scales, although it being an ancestral galaxiid that had not yet developed galaxiid traits could not be ruled out. Other taxonomic treatments have instead placed Stompooria as part of an extinct clade sister to the Esociformes and Salmoniformes.
Many galaxiid genera show an unusual form of sister group relationship to one another, where a genus in Australasia is more closely related to a genus in South America than to other genera from the same continent. An example is the relationship between the South American Aplochiton and the Australian Lovettia. It is thought that the evolution of galaxiids may have been influenced by the Antarctic land bridge between Australia and South America, which served as a shallow marine and fresh water connection that allowed different galaxiid taxa to disperse between both continents.

Taxonomic diversity

About 50 species are in the family Galaxiidae, grouped into seven genera:

Genera

  • ?†Stompooria Anderson, 1998
  • Subfamily Aplochitoninae Begle 1991
  • * Genus Aplochiton Jenyns 1842
  • * Genus Lovettia McCulloch 1915
  • Subfamily Galaxiinae
  • * Genus Brachygalaxias Eigenmann 1928
  • * Genus Galaxias Cuvier 1816
  • * Genus Galaxiella McDowall 1978
  • * Genus Neochanna Günther 1867
  • * Genus Paragalaxias Scott 1935

    Species by geography

Australia

Galaxiids are found around the south eastern seaboard of Australia and in some parts of south western Australia. The galaxiids and the temperate perches are the dominant native freshwater fish families of southern Australia. Species common to all areas include:
South east Australian mainland
Threatened species are:
Western Australia
Tasmania
Seventeen species of galaxiids have been found in Tasmania. The most common species are:
  • Climbing galaxias, Galaxias brevipinnis
  • Common galaxias, Galaxias maculatus
  • Spotted galaxias, Galaxias truttaceus
Tasmanian endangered species include:
Twenty-three species of galaxiids have been discovered in New Zealand, and prior to the introduction of non-native species such as trout, they were the dominant freshwater fish family. Most of these live in fresh water all their lives. However, the larvae of five species of the genus Galaxias develop in the ocean, where they form part of the zooplankton and return to rivers and streams as juveniles, where they develop and remain as adults. All Galaxias species found in New Zealand are endemic, except for Galaxias brevipinnis and Galaxias maculatus.
The juveniles of those galaxiids that develop in the ocean and then move into rivers for their adult lives are caught as whitebait while moving upstream and are much valued as a delicacy. Adult galaxiids may be caught for food, but they are generally not large. In some cases, their exploitation may be banned unless available to indigenous tribes.
In addition to serious impacts from exotic trout species, Australian adult galaxiids suffer a disregard from anglers for being "too small" and "not being trout". This is despite the fact that several Australian galaxiid species, though smallish, grow to a sufficient size to be catchable and readily take wet and dry flies, and that one of these species — the spotted galaxias — was keenly fished for in Australia before the introduction of exotic trout species. A handful of fly-fishing exponents in Australia are rediscovering the pleasure of catching these Australian native fish on ultralight fly-fishing tackle.