Genus of fishes
Galaxias is a genus of small freshwater fish in the family Galaxiidae, and are frequently referred to as the galaxiids. These highly adaptable fish are typically found at temperate latitudes across the Southern Hemisphere.
Galaxiids are scaleless and somewhat tubular in body form, ranging from very slender to quite bulky. They are somewhat torpedo-shaped, with the dorsal and anal fins positioned close to the tail. They are generally small, with typical adults ranging between in total length, with some stocky species attaining around . The largest, "Galaxias argenteus", has been recorded at , although is a more typical adult length.
Species.
The 46 recognized species in this genus are:
Distribution.
Galaxiids are restricted to the Southern Hemisphere, and generally only occur in temperate latitudes. Only one species is known from subtropical habitats.
Galaxiids are the dominant group of native freshwater fish in New Zealand, and, along with the Percichthyidae, one of two dominant groups of native freshwater fish in southeastern Australia. Only one of the species ("G. zebratus") is found in Africa, and only three ("G. globiceps", "G. maculatus", and "G. platei") are found in South America. One species ("G. neocaledonicus") is endemic to the New Caledonia
Habitat.
Galaxiids are coolwater species, with many wholly freshwater species specialising in high-altitude upland streams (including very small streams), rivers, and lakes. Some galaxiids include a marine stage in their lifecycles where larvae are washed out to sea to develop, and return to rivers as juveniles. This type of diadromous fish migration is known as amphidromy. These species are consequently also found in low-altitude habitats, but frequently migrate to high-altitude reaches of river systems in their adult stage.
Threats.
Wholly freshwater galaxiids are gravely threatened by exotic salmonid species, particularly exotic trout species, which prey heavily upon them and compete with them for food and habitat. This is a major concern, as exotic trout species have been introduced to many different land masses (e.g. Australia, New Zealand, South Africa) with no thought as to impacts on native fish such as galaxiids, and no attempt to preserve some exotic trout-free habitats for native fish.
In most situations, wholly freshwater galaxiids are unable to persist in the presence of exotic trout species, and many are now restricted to the few remaining trout-free habitats. Where these species are found in the presence of trout, the galaxiids usually consist entirely of individuals which dispersed there from an upstream trout-free population, and are not self-sustaining. Numerous localised extinctions of wholly freshwater galaxiid species (i.e. mountain galaxias) have been caused by the introduction of exotic trout species (including ongoing illegal stockings) and a number of wholly freshwater galaxiid species are threatened with extinction by exotic trout species and other exotic salmonids.
Introduced salmoniids also have a negative impact on diadromous galaxiids, competing with them for food and habitat, as well as preying on them. However, the impact is not as great and they appear to be able to persist in the presence of trout.
References.
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