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.[2]
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 (e.g. Australia, New Zealand), 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.[1]
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.[3][4]
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 (Maastrichtian) galaxiid from South Africa was described as Stompooria.[5] 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.[6] Other taxonomic treatments have instead placed Stompooria as part of an extinct clade sister to the Esociformes and Salmoniformes.[4]
Galaxiids are found around the south eastern seaboard of Australia and in some parts of south western Australia. The galaxiids and the temperate perches (Percichthyidae) are the dominant native freshwater fish families of southern Australia. Species common to all areas 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 (whitebait), where they develop and remain as adults. All Galaxias species found in New Zealand are endemic, except for Galaxias brevipinnis (koaro) and Galaxias maculatus (inanga).
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 (e.g. New Zealand) 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 (and releasing) these Australian native fish on ultralight fly-fishing tackle.
^ abMcDowall, R. M. (2006). "Crying wolf, crying foul, or crying shame: Alien salmonids and a biodiversity crisis in the southern cool-temperate galaxioid fishes?". Reviews in Fish Biology and Fisheries. 16 (3–4): 233–422. doi:10.1007/s11160-006-9017-7. S2CID11504101.
