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.
Biology and Habitat
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 (approx. 120 mm length). 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. It is known to prey heavily on newly stocked trout.
Impacts on Native Fish
The 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, 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. EHNV has now been recorded from NSW, ACT, and Victoria. The perch is a voracious predator, with large and small individuals in the Basin consuming small native species such as carp, gudgeons and the young of Murray cod, Golden perch and trout.
Distribution and Abundance
The Redfin perch is native to the cooltemperate 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 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 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. The perch is a popular angling species, particularly in Vic.