A small, deep-bodied fish with a slightly forked tail Maximum size is 640 mm; usually<400 mm (larger fish are found in lakes rather than ponds). Maximum weight recorded is 4.7 kg; fish of up to 2 kg are commonly recorded from lakes. Like Carp and goldfish, it has 3–4 stout spines at the front of the dorsal fin. The largest dorsal and anal spines serrated on the trailing edge.
The body is a golden-bronze colour, darkening with maturity to a dark green back, bronze upper sides, and gold on the lower sides and belly. Unlike Goldfish, Individuals do not become rotund when large. Both sexes develop fine nuptial tubercles on the body, fins and head.
Crucian carp was only confirmed as occurring in Australia in 2006. From the late 1800s it was considered as present in Australia, and in 1971 the species was still listed by John Lake as present. However by 1980 the earlier reports of the species presence was thought to represent confusion with Goldfish, and so the species was deleted from Australian fish lists.
Crucian carp look similar to Goldfish but can be distinguished by the following characters: fewer (21–32) and shorter gill rakers; dorsal fin edge is curved outwards (convex); scales are small; lateral line scale count is 32–34; caudal fin shallowly forked; body strongly laterally compressed; black spot on caudal peduncle in juveniles. It is unknown whether Crucian carp hybridise with Goldfish or Carp in Australia.
Nothing is known of the ecology of the species in Australia, so information below is from Europe. Crucian carp has a wide environmental tolerance, surviving in pH down to 4; temperatures from 0-38 °C; and around 6 months of anoxia in dark, near-freezing water temperatures in small ponds when it overwinters under ice. It is also reported to burrow into mud in drying habitats. Over winter the species hibernates; ceases feeding and becomes inactive.
Crucian carp has a strong preference for slow-flowing (almost stagnant) lowland rivers or lakes. Like Goldfish, it is often found in association with submerged or emergent freshwater plants, but it is not a schooling species, being a rather inactive occupant of the littoral zone.
In northern Europe the species often occurs alone in high densities (up to 70,000/Ha) in ponds, generally dominated by small individuals (>100mm). In lakes where other species are present, densities are much lower (<100/Ha and fish are larger (>200 mm). In dense populations juvenile mortality can be high due to cannibalism. The sex ratio of small fish is usually 1:1, but most larger individuals are females. Sexual maturity of Crucian carp is variable, (depending on water temperature, population density and growth) occurring between 1–4 years of age.
The species is a fractional spawner, laying eggs in a number of batches (often 3–5) during summer. Spawning occurs in dense submerged vegetation from late spring to early summer at water temperatures of 17–20 °C; the eggs hatch after 5 days at 18–20 °C; fry are 4.2–5.5 mm upon hatching. Fecundity is size dependant, with a 100 mm fish containing ~600 eggs and a 200 mm fish ~7000, but not all these are spawned. Fertilised eggs are small, between 1–2 mm diameter, and adhere to water plants.
Crucian carp feed all day, but mostly at night. The diet contains mainly planktonic and benthic invertebrates, but plant material detritus and phytoplankton are also recorded. In lakes molluscs, chironomid larvae and cladocerans are important dietary components.
The species is extremely vulnerable to predation. In Europe the species avoids predation by occurring in habitats where other fish cannot survive, altering its body shape (becoming deeper in the presence of predators), or occupying dense vegetation. Body depth of 200mm individual without predators present is ~60 mm, whereas it is 90 mm with predators. Lifespan is about 10 years; size at age is variable, a 6 year old fish can be only 130 mm, or a 3 year old can be 250 mm; but generally growth is about 15–40 mm/year.
As a result of the long-standing confusion about the presence of Crucian carp in Australia, nothing is known of its impacts on native fish. Like Goldfish, the species is possibly a relatively ‘benign’ introduction to Australia. It is unlikely to be a significant predator, but may have some impacts on egg masses of native fishes that deposit benthic or macrophyte-attached eggs. Crucian carp is often used as baitfish in Europe.
Crucian carp is native to Europe and were first thought to have been introduced into Australia in the 1860s when they were imported along with Carp and Goldfish. The species has a very restricted known distribution in the Murray-Darling Basin being only known from the Campaspe drainage in Vic.
However, confusion and misidentification with Goldfish means that all pre-2006 records need to be treated with caution, though no specimens have yet been located in Australian museum collections (Raadik, T.A. pers. comm. 2021). 9 individuals were recorded from the Sustainable Rivers Audit (2004–2013) and 4 from the MDB Fish Survey (2014/15–2021/22).
Clements 1988; Holopainen & Pitkänen 1985; Holopainen et al. 1997; Penttinen & Holopainen 1992; Pettersson et al. 2001; Raadik 2007; Sayer et al. 2011.
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