The Old World silversides are a family, Atherinidae, of fish in the order Atheriniformes. Atherinidae are abundant and considered bony fish (teleost) that are widespread globally, living in rivers, estuaries, and coastal waters. They occur worldwide in tropical and temperate waters. About two-thirds of the species are marine, and the remainder live in fresh water. The 74 species are in 13 genera. The genus Craterocephalus is the most diverse with 25 species. Four genera are monotypic. Silversides are relatively small with most being less than in length, with several not attaining lengths of more than . The body is generally elongated. Distinctive characters include two dorsal fins widely separated, with the first consisting of flexible spines and the second having one spine followed by soft rays, while the anal fin has one spine on the leading edge followed by soft rays. The pectoral fins tend to be high, and there is no lateral line. On the flanks is a broad, silvery band. The scales are relatively large. They feed on zooplankton. Some species, such as the hardyhead silverside, Atherinomorus lacunosus, are commercially fished. The family Atherinopsidae (Neotropical silversides) is closely related, while the genus Atherion has been given family status in the Atherionidae by some authorities. Subfamilies and genera According to the 5th edition of Fishes of the World the family should be classified as follows: Subfamily Atherininae Risso, 1827 Atherina Linnaeus, 1758 (7 species) Atherinason Whitley, 1934 (monotypic) Atherinosoma Castelnau, 1872 (2 species) Kestratherina A. Pavlov, Ivantsoff, Last & Crowley, 1988 (2 species) Leptatherina Pavlov, Ivantsoff, Last & Crowley, 1988 (2 species) Subfamily Atherinomorinae Dyer & Chernoff 1996 Alepidomus C. L. Hubbs, 1944 (monotypic) Atherinomorus Fowler, 1903 (11 species) Hypoatherina Schultz, 1948 (15 species) Stenatherina Schultz, 1948 (monotypic) Teramulus J.L.B. Smith, 1965 (2 species) Subfamily Bleheratherininae Aarn & Ivantsoff 2009 Bleheratherina Aarn & Ivanstoff, 2009 (monotypic) Subfamily Craterocephalinae Dyer & Chernoff 1996 Craterocephalus McCulloch, 1912 (26 species) Sashatherina Ivantsoff & Allen, 2011 (monotypic) Subfamily Craterocephalinae Origin and Characteristics of genus Craterocephalus In the silverside family Atherinidae, the genus Craterocephalus is the only one containing primarily freshwater species and is the most speciose. It is also the only genus that experienced high levels of radiation in freshwater ecosystems. Overall, there are twenty-five species, of which twenty are freshwater organisms and five are marine fish found only in Australian coastal waters. Within the genus, numerous species live in Australia’s freshwater ecosystems,