Fish Facts

FISH FACTS: Silver perch

The silver perch is considered threatened or endangered throughout its range (image: Ken Smith).

THE silver perch (Bidyanus bidyanus), also known as Murray perch or black bream, is one of Australia’s more interesting native freshwater fishes. Unlike the two other main species of large recreationally targeted fish native to the Murray-Darling river basin (Murray cod and yellowbelly), the silver perch is classified in the Family Terapontidae and thus is more closely related to grunters, including species like spangled perch, and the sooty and Barcoo grunters.  Its closest relative is, however, Welch’s grunter (Bidyanus welchi), which was first encountered by Europeans in 1861 from Coopers Creek and is native to the drainages of Lake Eyre and the Barcoo, Diamantina and Georgina Rivers. In contrast, silver perch were first described by Europeans in 1838 from the area between the Gwydir and McIntyre Rivers, where they were called bidyan by the Aboriginal people of the area, hence their scientific name.

The silver perch is endemic to Australia, occurring mainly in the faster flowing reaches of inland rivers throughout the Murray-Darling drainage from Queensland, through New South Wales, Victoria and South Australia. This species has also been introduced into the Lake Eyre Basin as well as several impoundments and coastal river systems of south-eastern Queensland, New South Wales and south-western Western Australia as part of restocking efforts.  It is also now farmed in many places throughout its natural range as well as in several areas of Asia.

Adult silver perch are omnivorous, feeding on a variety of small prey including zooplankton, insect larvae, molluscs, crustaceans and worms as well as algae.  In many parts of their range the amount of algae in the diet tends to increase with fish size.  Silver perch are a highly migratory species which tend to move upstream during river flow events.  These migrations are thought to have evolved as part of the spawning behavior of adult fish to compensate for the inevitable downstream drift of eggs and larvae that occurs after spawning takes place. Upstream movements of 10s to 100s of km are commonly recorded, including one tagged fish that travelled over 500 km upstream in less than 2 years.  Most of the adult fish tend to move upstream in a short spawning run period between November to February, while immature fish may move upstream over a longer period between October to April. Spawning occurs in the late afternoon or evenings in faster flowing areas of the river over gravel or rock rubble substrates.

As regulation of the Murray-Darling system increased over the course of the 20th century, the size and frequency of these upstream spawning runs decreased and many populations of silver perch had collapsed by the 1980s. Construction of dams, locks and weirs resulted in numerous barriers to fish migration that fragmented silver perch habitat and prevented the recolonisation of extensive stretches of river.  Recent constructions of native fish friendly fishways on several weirs have improved this situation along the middle and lower reaches of the Murray River, but silver perch populations remain endangered in many other regions due to a myriad of factors including siltation that reduces spawning habitat and survival of silver perch eggs and larvae, diversion of eggs and larvae into irrigation water, cold water pollution from dams, and introduced diseases.  Because of the persistence of these many threats, the species is considered threatened or endangered throughout its range.

Female silver perch grow to a larger size than males, reaching a maximum size of around 45 cm and 7-8 kg. Growth varies between individual fish and is affected by the productivity of their environment. Sexual maturity is reached in three years for males at around 25 cm long, while females mature in 4 to 5 years at around 29 cm long. Maximum age is at least 17 years for river fish and 27 years for fish in impoundments. 

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