Old World silverside

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 20 cm (7.9 in) in length, with several not attaining lengths of more than 5 cm (2.0 in). 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.

With reference to the 5th edition of Fishes of the World and the 2020 introduction of the genus Doboatherina, the family should be classified as follows:

The oldest known Old World silverside is "Atherina" macrocephala Agassiz, 1835 from the Early Eocene-aged Monte Bolca site of Italy. The fossil genus †Hemitrichas Peters, 1877 contains multiple species commonly found in late Eocene to early Miocene fossil deposits of Europe.

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, specifically, 18 species live in Australia, 6 in New Guinea, and 1 in East Timor. How Craterocephalus diverged from being marine water organisms is linked to the ancestors of Craterocephalinae and Atherininae, where both subfamilies lived in similar environments but were separated by a North-South disjunction around Australia. The separation caused one lineage to remain in Northern Australia, forming the genus Craterocephalus, which developed distinct characteristics from the other subfamily Atherininae. Since all of Atherinidae are primarily marine, Craterocephalus is most likely also of marine origin.

Freshwater fish in the genus Craterocephalus are found in various ecosystems, such as rivers, rainforest streams, creeks, and hot desert springs. Characteristics of the fish include having short life spans that are 2–3 years long, and their body length ranges from 5–10 cm. Maturity is reached when fish are 3–5 cm in length, and most species spawn shortly after one year of being born. Spawning rates increase in the spring and continue to be high in the summer — typically, one fish releases 85 eggs daily. Species in this genus are tolerant of environments differing in salt concentrations and temperature, especially C. eyresii and C. cuneiceps. Both these species can tolerate 70–100 ppm of salt, while C. dalhousiensis can withstand high water temperatures up to 42 °C.