The single dorsal fin has a higher, spinous anterior section and a lower, rayed section at the rear. The body colour is grey to grey-brown with a lighter belly. The scales are much smaller than those on Golden or Macquarie perch, and the head and mouth are small. The tail is weakly forked.
Biology and Habitat
Silver perch are found in similar habitats to Murray cod and Golden perch, i.e. lowland, turbid and slow-flowing rivers. This species is bred artificially in a number of government and commercial hatcheries and widely stocked into farm dams and reservoirs. It has been the subject of considerable interest for its potential as an aquaculture species. Individuals mature at 3–5 years—males earlier than females. They spawn in spring and summer after an upstream migration, when large schools often form. Spawning possibly occurs at night, just after dusk. Whilst spawning can occur during nonflood conditions, spawning activity was significantly increased during a flood and environmental water release in 2005 in the mid-Murray River. Immature individuals have been recorded moving through fishways in the Murray and Murrumbidgee rivers. Murrumbidgee fish moved during afternoon and dusk periods, and fish as small as 68 mm were involved. Silver perch are omnivorous. The diet contains aquatic plants, snails, shrimps and aquatic insect larvae. Reports that the species becomes mainly herbivorous once it reaches lengths of 250 mm are incorrect, at least for lake populations, as diet in Googong Reservoir near Canberra shows little change with fish size.
Distribution and Abundance
Formerly widespread over much of the Murray-Darling Basin excluding the most upper reaches, Silver perch has declined over most of its range. Numbers moving through a fishway at Euston Weir on the Murray River declined by 93% between 1940 and 1990. Only nine Silver perch were recorded in a two-year survey of 40 randomly selected sites in the NSW portion of the Basin in the mid 1990s. Similarly, the first 2 sampling rounds of the Sustainable Rivers Audit has so far only recorded a total of 20 Silver perch whilst surveying 351 randomly selected sites covering 16 river valleys. The species is still patchily abundant in the mid-Murray. The ACT probably represented the upstream limit of distribution in the Murrumbidgee catchment, although the large spawning run of fish that occurred in summer from Lake Burrinjuck is unfortunately a thing of the past.
Potential Threats
River regulation has severely affected this species through disruption of migration and reproductive behaviour. Thermal pollution and interactions with alien species (Carp and Redfin perch) are also suspected to be a threat.