Identification
Commonly known as Agassiz’s Olive Perchlet, this delicate species is a master of minimalism. Reaching a modest 7–8 cm, its body is deep and laterally compressed, characterized by a distinctively notched dorsal fin. Its most striking feature is its semi-transparency; the body possesses a diaphanous, olive-yellow sheen that allows a clear glimpse of the vertebral column. To distinguish it from similar glassfish in the field, look for the fine, dark mid-lateral line and the large, silver-rimmed eyes. Unlike the estuarine *Ambassis jacksoniensis*, Agassiz’s lacks the dark blotch on the first dorsal fin and is strictly a freshwater specialist.
Habitat & Range
These "glassfish" are icons of the Murray-Darling Basin and the coastal rivers of eastern Australia. They are specialists of "slack water"—think billabongs, backwaters, and the quiet, sun-dappled margins of rivers. They avoid high-flow channels, preferring the labyrinthine protection of dense aquatic vegetation (macrophytes) or "snags" (submerged woody debris) in lowland elevations.
Behaviour
Highly social and somewhat nervous, these fish form shimmering schools that hover near cover. An observer will notice their "dart-and-hover" swimming style; they hang motionless in the water column before making a lightning-fast adjustment. During the spring and summer breeding season, they become more frantic, with females scattering adhesive eggs among aquatic plants. They are shy; a sudden shadow on the bank will send the entire school vanishing into the weeds in a synchronized, silvery flash.
Diet
Agassiz’s Perchlets are opportunistic micro-carnivores. They spend their days hovering in the water column, snapping up tiny crustaceans like cladocerans and copepods, as well as drifting aquatic insect larvae.
Fascinating Fact
Because of their remarkable transparency, you can often see their internal organs and the silvery, pointed sac of their swim bladder pulsing through their skin—it is like watching a living X-ray swimming through the reeds!