Ambassis jacksoniensis

William John Macleay described the Port Jackson glassfish as Pseudambassis jacksoniensis in 1881 from a specimen collected in Port Jackson, noting that the length was three and a third times the fishes' height.[2] The species name relates to the location it was described.[1] It was classified in the new genus Velambassis by Gilbert Whitley in 1935, on the basis of having weaker dorsal spines than other members of the family.[3] Allen and Burgess found no reason for the species not to be in the genus Ambassis and reassigned it there in 1990.[4]

This species and the co-occurring estuary glassfish (A. marianus) are the only two members of the genus found in temperate waters. The others are found in the waters of northern Australia and southeast Asia.[4]

Reaching a standard length of 7 cm (2 ³⁄₄ in), the Port Jackson glassfish has a silver and semi-transparent body and head covered with large cycloid scales. It has a short deeply-notched dorsal fin and forked tail fin.[1] It is slimmer than the related A. marianus—its body depth is 33 to 38% of standard length compared to the latter species' body depth of 37 to 44% of standard length. The Port Jackson glassfish also has a lateral line running the length of its body, while that of its relative is partial.[4]

The Port Jackson glassfish is native to coastal eastern Australia, from Moreton Bay in Queensland through to Narooma in southern New South Wales.[1] It lives in estuaries and protected brackish tidal streams that have mangroves growing along the margins.[4]

The Port Jackson glassfish feeds on zooplankton, foraging from the water surface to the substrate.[1] It is a food item of the little pied and little black cormorants.[5]