A medium sized and deep-bodied fish with a slightly forked tail, two separate dorsal fins and a large mouth which reaches to under the eye. Maximum length 500 mm and weight 10 kg; commonly 400 mm and 1–2 kg. The back is olive-green to grey, paling on the sides to white on the belly. There are usually around six black bands on the back, tapering on the sides. The pelvic and anal fins and margins of the tail are bright red or orange-red, which is the origin of the common name.
Redfin perch mainly occur in slow-flowing or still water habitats, such as lakes, billabongs and swamps, especially where freshwater plants are abundant. Individuals are generally mature after 2–3 years, but males may mature at the end of the first year. A characteristic of the species is the propensity to ‘stunt’ under conditions of poor food availability or overcrowding, when individuals can mature at a very small size (~ 120 mm length). Growth is highly variable and can depend on food availability, water temperature, population density and predation risk.
Spawning occurs in spring when water temperature reaches 12°C. Thousands of eggs are laid as gelatinous ribbons amongst freshwater plants. The eggs are 2–3 mm in diameter and the larvae hatch in 1–2 weeks with juvenile fish forming large schools. The Redfin perch is a pelagic carnivore with a diet that includes crustaceans (shrimps, yabbies and other freshwater crayfish), zooplankton and small fish such as Western carp gudgeon, galaxiids and Eastern gambusia, and the threatened pygmy perches. It is known to be cannibalistic, and also to prey heavily on newly stocked trout. A preliminary movement study in a dam in NSW found that the individuals were very active both at night and day, and in the lower Murray River significantly more individuals were caught below weirs at night than during daytime electrofishing.
Redfin perch is the main host for Epizootic Haematopoietic Necrosis Virus (EHNV). This virus, unique to Australia, was first isolated in 1985 on Redfin perch and is characterised by sudden high mortalities of fish. Laboratory trials have demonstrated that Macquarie perch, Silver perch, Rainbow trout and Mountain galaxias are among several species found to be extremely susceptible to the disease, but the impacts in the wild are as yet unknown. Murray–Darling rainbowfish and Freshwater catfish are considered to be potentially susceptible to EHNV, but Murray cod and Golden perch are not. Eastern gambusia are a potential carrier of the disease. Tests on Unspecked hardyhead, Carp gudgeon, Trout cod, Southern purple-spotted gudgeon and Southern pygmy perch did not show any clinical signs of EHNV after exposure to the virus. EHNV has been recorded historically from NSW, ACT, SA and Victoria, but recent studies suggest it is now largely confined to the upper Murrumbidgee drainage.
The Redfin perch is a voracious predator, with large and small individuals in the Basin consuming small native fishes such as carp gudgeons, Southern pygmy perch, and the young of Murray cod, Golden perch and trout. In Lake Alexandrina in SA, a recent study found that most juvenile redfin perch (95–128 mm TL; <1 year old) occupied a variety of habitats where they largely prey on small-bod- ied native fishes including Tamar goby, Lagoon goby, Flat-headed gudgeon, Australian smelt, Bony herring and Small-mouthed hardyhead. Macquarie perch populations in the upper Lachlan drainage and Southern pygmy perch populations in Blakney Creek appear to be receding as the Redfin population expands.
Redfin perch is native to the cool temperate waters of the Northern Hemisphere. It was first introduced to Tas between 1858 and 1862 and to Vic in 1861. The species is widely distributed throughout the temperate portion of the Murray–Darling Basin, but absent from the colder, fast-flowing headwaters and the hotter reaches of the Darling drainage. It is not present in Qld. It survives in water temperatures of up to about 31°C, which largely explains its distribution. The species is occasionally moved illegally by anglers either into streams, or lakes as angling targets or into farm dams for future use as bait, and once established, can increase rapidly in numbers. In Lake Burley Griffin, Canberra, within six years of establishing it formed 58% of the total catch. However, these numbers declined dramatically after an outbreak of EHNV in the early to mid-1990s, and the species now comprises around 10–15% of the catch. Redfin perch is still expanding its range in the MDB, usually through being moved by people, and is currently invading parts of the upper Lachlan drainage. Redfin perch is a popular angling species, particularly in Vic. It was the fourth most abundant alien species (6,173 individuals) (behind Carp, Eastern gambusia and Goldfish) recorded from the Sustainable Rivers Audit (2004–2013), and was recorded in 18 river valleys, with 44% coming from upland and 27% from montane elevational zones. However, 60% of all individuals came from a single valley (Gwydir). 1,433 individuals have been captured from 17 river valleys in the MDB Fish Survey (2014/15–2021/22), with only 19.1% from the Gwydir valley.
Baumgartner et al. 2008; Becker et al. 2013; Langdon 1989; Lintermans et al. 1990b; McDowall 1996c; Morgan et al. 2002, 2005; Pearce 2015; Pen & Potter 1992; Weatherley 1963, 1977; Wedderburn & Barnes 2016; Whittington et al. 1996, 2011.
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