R. Wager and P. Jackson
Environment Australia, June 1993
ISBN 0 6421 6818 0
It is difficult to define an Australian freshwater fish. Only four fishes are considered to have evolved as primary freshwater species: Australian lungfish (Neoceratodus forsteri); northern saratoga (Scleropages leichardti); southern saratoga (S. jardinii) and salamanderfish (Lepidogalaxias salamandroides). The remainder of the freshwater fish fauna is considered to have evolved from marine ancestors. A criterion of inhabiting water with a salinity of less than three parts per thousand (the internationally accepted upper limit for fresh water) is inadequate for Australian fishes. Many inland waters often have high salinities and may be several times more saline than sea water. A criterion of inhabiting inland waters is also inadequate as many fishes generally considered to be freshwater species must migrate to estuaries or oceans to reproduce. Many marine or estuarine species spend considerable time in coastal freshwaters.
A working definition of freshwaters are those waters that are not estuarine, coastal or oceanic. Freshwater fishes are then considered to be those species that either:
- complete their life cycle without migrating to estuarine, coastal or oceanic waters; or
- exist in fresh water for a large portion of their life cycle; or
- exist in fresh water for long periods but that are primarily marine species.
Approximately 195 freshwater species and subspecies, representing 39 families, have been described from Australian waters. A further 22 undescribed taxa are currently recognised. In addition new taxa are likely to be described from several families including the Gudgeons (Eleotrididae), the Grunters (Terapontidae), and the freshwater Basses and Cods (Percichthyidae).
Since European settlement of Australia no freshwater fishes are known to have become extinct. However, assuming the total number of species is around 217, approximately 8% are threatened with extinction (including one species that is extinct in the wild) and 25% are considered to have seriously declined or occur in restricted areas. With the exception of a few species, all Australian freshwater fishes have probably undergone reductions in distribution and abundance since European settlement. Habitat modification and destruction, and introduced exotic species are primary causes of this decline. Those species that have not declined either (a) occur in remote wilderness areas, (b) have been able to utilise degraded or modified habitat, or (c) have been able to compete with introduced exotic species. A few native species have probably increased in abundance and the distributions of several species with angling potential have been extended through translocations.