Galaxias is a genus of small, highly successful freshwater fish in the family Galaxiidae. They are typically found at temperate latitudes across the Southern Hemisphere and are frequently referred to as galaxiids. 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.
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 southeasternAustralia. Only one of the species is found in Africa, and only three are found in South America.
Habitat
Galaxiids are coolwater species, with many wholly freshwater species specialising in high-altitude upland 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 exoticsalmonid 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 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 have been caused by the introduction of exotic trout species 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.
