A small laterally compressed fish, with a truncate to slightly rounded tail, and small, upturned mouth. Commonly 20-45 mm total length, but individuals >50 mm occasionally recorded. Possessing two separate dorsal fins, with breeding males have a distinctive, but variable red colouration in several fins. They can have a distinctive, longitudinal red band at approximately half the fin depth of the dorsal and anal fins, or red basal half on of the dorsal, caudal and anal fins. The red portion of the dorsal and anal fins is then edged with a thin whitish (or occasionally blueish) band near the outer fin edges.
Females have clear fins, and like other carp gudgeons have bright yellow-orange-coloured bellies in the breeding season. The midlateral scale margins are darker than in other MDB carp gudgeons, giving a slightly reticulated appearance.
Western carp gudgeon is found in still and slow-flowing waters including lakes, dams, rivers, creeks and billabongs. It is normally associated with macrophyte beds or other aquatic vegetation. It spawns in late spring and summer when water temperatures exceed 20 °C. Early studies of reproduction in Western carp gudgeon at the Narrandera Research Station recorded that spawning occurred when water temperature exceeded 22.5°C. Mature females of 30-50 mm length may lay up to 2,000 small, (0.5 mm diameter), adhesive eggs.
Spawning occurs quite close to the water surface with the eggs being deposited on submerged aquatic vegetation or twigs. The male guards and fans the eggs. Hatching occurs after about 50 hours, and newly hatched larvae are 1.8–2.1 mm long. Feeding commences 5 days after hatching, and by day 6 they are free swimming.
The Western carp gudgeon is the only species present in the ACT and surrounding NSW waterbodies of the upper Murrumbidgee catchment and is primarily a mid-water carnivore although some benthic feeding also occurs. At this site important dietary items include copepods, aquatic insects, ostracods and cladocerans, with chironomids the most frequently consumed aquatic insect. Western carp gudgeon is abundant in the Canberra region where it can form a substantial portion of the diet of Golden perch, Redfin perch and Brown trout. It also forms part of the diet of piscivorous birds such as cormorants.
Western carp gudgeon do not hybridise with other carp gudgeons.
In a study in the mid Murrumbidgee River, Western carp gudgeon had the lowest parasite richness (3 taxa) and overall parasite prevalence (39% of fish) compared to hemiclonal Midgleys and Lakes carp gudgeons which had more than twice the parasite richness and prevalence of infection of >90%
The species is widespread and abundant throughout the MDB. The species is also present in the adjacent Bulloo River, Cooper Creek, and eastern coastal streams in the Hunter River and then from the Clarence River north to the Styx system (Rockhampton), with a disjunct northern population in the Burdekin River.
This is the only carp gudgeon species found in arid Paroo catchment and in the upper Murrumbidgee catchment above Burrinjuck dam. Records of this species would also be included within the general ‘carp gudgeon’ map, but the taxonomic confusion means that these records cannot be separated out.
The species is widespread and abundant. However, in the ACT, significant kills of Western carp gudgeon have occurred as a result of infestation with the introduced tapeworm Bothriocephalus acheilognathi. Predation by alien fish such as Redfin perch in floodplain ponds/billabongs can significantly reduce local abundance.
Bowling 1981; Cadwallader 1979; Dove et al. 1997; Lake 1967 a,b; Mockler 1994; Rochat et al. 2020; Thacker et al. 2022; Unmack 2000, 2019.
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