Described by Austrian naturalist Rudolf Kner in 1866, it comprises two subspecies that have been regarded as separate species in the past and may be once again with further study.

A small silvery fish averaging around 3.25 cm in total length (1+1⁄8–1+3⁄8 in), the Pacific blue-eye is recognisable by its blue eye-ring and two dorsal fins.

[4] British entomologist William Sharp Macleay named a "curious little fish" collected from the Bremer River, a tributary of the Brisbane River, by one Mr Jameson of Ipswich, Atherinosoma jamesonii in 1884; it was later classified as the same species by Australian ichthyologist James Douglas Ogilby in 1908.

[4] In their 1919 monograph of the family Atherinidae, David Starr Jordan and Carl Leavitt Hubbs maintained the two as separate species—P.

[4] The Pacific blue-eye can be distinguished from the highly invasive and noxious introduced eastern mosquitofish (Gambusia holbrooki) by its forked tail fin.

Fish species it is commonly found with include Marjorie's hardyhead (Craterocephalus marjoriae), crimson-spotted rainbowfish (Melanotaenia duboulayi), Australian smelt (Retropinna semoni) and western carp gudgeon (Hypseleotris klunzingeri).

[14] A field study in two lakes polluted by coal mine runoff in central Queensland found that the Pacific blue-eye was more resistant than tadpoles of the striped marsh frog (Limnodynastes peronii) to adverse health effects.

They are generally found in the middle to upper water column within 1 metre (3 ft) of the riverbank and often close to underwater cover.

[16] In a school of Pacific blue-eyes that is threatened, a few individuals accelerate and change direction, which initiates an escape wave that spreads through the whole cohort.

[18] Female Pacific blue-eyes are sexually mature at six months of age or when they have reached 2.3 cm (7⁄8 in) in standard length.

[4] A study published in 2003 showed that males will preferentially choose larger females—who are more fecund as a rule—unless more energy is required to do so, such as swimming further against a current.

[4] An experiment housing Pacific blue-eyes and mosquitofish together showed that the growth and breeding of the former fish were severely affected by the presence of the latter.

The mechanism was unclear—there were some signs of direct aggression (bite marks on fins of Pacific blue-eyes) but stress from contact was thought to be a major factor.

[4] Field work on Narrabeen Lakes showed that Pacific blue-eyes spent time near the surface looking for dead flying insects, consuming anything below their mouth gape size.