A small, deep-bodied fish with a forked tail and a small, protrusible mouth that does not reach back to below the eye. Maximum size 400 mm and 2 kg; usually <200 mm in the MDB. Easily distinguished from Carp by the absence of barbels around the mouth. Like Carp, it has 3–4 stout spines at the front of the dorsal fin, the largest one serrated on the trailing edge. The back is usually olive-bronze to golden, paling to silvery-white on the belly. Occasionally, the classic aquarium colour of orange-red is seen in wild specimens, as is the fan-tail.
Individuals can be quite rotund when large, particularly females. Males have fine nuptial tubercles on the body, fins and opercula. Goldfish look similar to Crucian carp (only confirmed as occurring in Australia in 2006) but can be distinguished by the following characters: more numerous (35-48) and longer gill rakers; dorsal fin edge is straight or curved inwards (convex); scales are larger; lateral line scale count is fewer (27-29); caudal fin is deeply forked; body is laterally rotund; no black spot on caudal peduncle in juveniles.
It is unknown whether Goldfish hybridise with Crucian carp in Australia, although it has been demonstrated elsewhere.
The Goldfish is usually associated with warm, slow-flowing lowland rivers or lakes, although it is also known from weedbeds and slower-flowing areas of upland rivers. It is often found in association with submerged or emergent freshwater plants such as Ribbon-weed (Vallisneria), Bullrush (Typha) and Common reed (Phragmites).
Individuals generally mature at 100–150 mm length, although they can be mature at 30–50 mm, and spawn during spring-summer at water temperatures of 17–23°C. Multiple batches of eggs are laid amongst freshwater plants and hatch in about one week. In the Barmah-Millewa Forest, the abundance of goldfish larvae was significantly higher in wetland habitats than creek or lake habitats, and in the Lower Murray in SA during the Millennium Drought the species was positively associated with submerged macrophytes.
Growth is variable depending on habitat, with reservoir, lake or wetland fish reaching 130 mm after a year, and stream fish usually considerably smaller. The fastest known growth rate for the species (~180 mm TL after a year) was recorded in the regulated, eutrophic Vasse River in south-west WA.
Previously Goldfish was considered to be relatively sedentary but a recent study in WA found that the average minimum distance moved by large fish was ~109.5 km over 12 months, with one fish moving at least 231 km. Movement could be relatively rapid, with one fish moving 5.4 km in 24 hrs. In the MDB Goldfish has been recorded moving laterally between rivers and floodplain wetlands in the lower Murray River in SA.
Similarly in WA it has been recorded making a seasonal migration to off-channel wetland sites in the Vasse River catchment, with this movement assumed to be spawning related. A study in the mid-Murray found that the abundance of age 0 Goldfish was positively correlated to short-term inundation of floodplain wetlands.
It is a benthic omnivore and its diet includes small crustaceans, freshwater insect larvae, plant material and detritus. It can also form a large component of the diet of predatory fish and of the 46% of Brown trout that had consumed fish in the Cotter Reservoir near Canberra, Goldfish comprised 90% of the fish recorded in stomachs. It can also form a large proportion of the diet of birds such as cormorants.
A consignment of Goldfish from Japan to Victoria is believed to be responsible for introducing to Australia the disease ‘Goldfish ulcer’, which also affects salmonid species. It is also often heavily infested with the parasitic copepod Anchor worm (Lernaea cyprinacea). Apart from the introduction of disease, the species is generally regarded as a ‘benign’ introduction to Australia and New Zealand.
However it must be noted that there has been relatively little research directed at this species in Australia and its benthic feeding activity (like Carp) could potentially have negative ecological impacts in some systems. It can also occur in large numbers in some habitats which then support increased predator abundance (both fish and birds).
Goldfish is native to eastern Asia and was first introduced into Australia in the 1860s when it was imported as an ornamental fish. Widespread in the MDB, it is often present in substantial numbers in the early years following construction of impoundments. In Cotter Reservoir the abundance of Goldfish increased significantly after the reservoir was enlarged, flooding new ground. Goldfish abundance in lakes usually declines after the stocking of predatory species such as Murray cod, Golden perch and trout, which consume large numbers of the species.
In a survey of SA wetlands in the Lower Murray, Goldfish was present in 65–80% of wetlands. 7939 individuals (3.6% of total fish catch) were caught in the Sustainable Rivers Audit (2004–2013) with the species captured in every river valley: 83% of Goldfish captured were in lowland zones (0–200 m elevation), 6.7% from uplands, 5.7% from slopes and 4% from montane zones. 3008 individuals have been captured in the MDB Fish Survey (2014/15–2021/22), again from all river valleys.
Allen et al. 2002; Beatty et al. 2017; Beesley et al. 2014a; Bice et al. 2014; Brumley 1996; Clements 1988; Conallin et al. 2011; Ebner et al. 2007a, 2009b; King et al. 2007; Merrick & Schmida 1984; Mitchell 1979; Moffat & Voller 2002; Morgan & Beatty 2007; Smith et al. 2009.
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