A medium-sized and thickset fish with a slightly forked tail. In the MDB it attains a maximum size of 840 mm and nearly 9 kg; usually 100–300 mm and 0.5–2 kg. The head is large with a long, blunt snout and small, distinctively orange-red eyes. The mouth is small to moderate in size with a single, small barbel at each corner.
The fins are rounded and thick. It has a single, short-based, high, and rounded dorsal fin, located on about the middle of the back. Some sexual dimorphism is present in fish > 2 years of age with males having larger pelvic fins, enlarged second pelvic fin rays and a muscular protuberance extending from the flank. The scales are very small and covered with a heavy mucous. Usually, dark olive to pale golden or silvery in colour.
Tench avoid fast water, and is typically found in slow-flowing or still habitats, often with a muddy bottom and abundant aquatic plants. It is often abundant in off-channel habitats, such as backwaters and lagoons, and in deep, sheltered holes.
Adult Tench are predominantly benthic carnivores, and their diet consists mainly of aquatic insects (commonly chironomids, mudeyes, mayflies) and microcrustaceans (cladocera, ostracods, amphipods, copepods), with some molluscs, worms and plant material. Small Tench feed largely on microcrustaceans and small chironomids. Fry feed on plankton and small insect larvae and crustaceans. Tench is nocturnal and so are probably more reliant on taste and olfactory rather than visual cues to locate prey; hence they can survive well in turbid environments.
Tench may live for 20–30 years and reach maturity at 3–4 years. In rivers, growth is generally slow: fish from the Coal River in Tas reached lengths of approximately 29, 57, 93, 132, 172, 208, 239 and 261 mm at 1 to 8 years of age, respectively. Growth is likely to be faster in the warmer environments of the MDB.
Spawning occurs in late spring and summer when water temperatures exceed 16–18°C. Females produce large numbers (300,000–900,000) of small eggs (0.8–1.0 mm diameter) in 3–4 batches, at intervals of about two weeks. The eggs are adhesive and laid in shallow water, usually on weeds. Hatching occurs after about 1 week at 16–20°C and hatchlings are about 4–5 mm in length.
Tench was a favoured dietary item of Murray cod in Lake Mulwala in the late 1970s, but had largely disappeared from this waterbody by the early 1980s (replaced by Carp). In Europe it was curiously believed that the abundant mucous slime of Tench could cure the wounds of other fish, with wounded fish cured by ‘touching’ Tench (hence its alternative common name of doctor fish).
Little is known of the impacts of Tench on native fish species, but they are not thought to be significant. Tench do not prey on native fish.
Tench is native to Europe but was introduced to Australia (Tas) in 1876 after being introduced into New Zealand in 1868. It was introduced into NSW in 1886. The species was originally widely distributed in Vic by acclimatisation societies and is still highly sought after by ‘coarse fish’ enthusiasts. J. O. Langtry recorded that it formed 21% of the catch in the Loddon River in 1949 but it only formed 1.4% of the catch in the Loddon from 2004–13 in the Sustainable Rivers Audit. In the Basin it is primarily restricted to Vic, being rarely recorded in NSW, but was formerly present in the Murray, lower Darling, lower Murrumbidgee and lower Lachlan rivers. J. O. Langtry recorded the species as abundant around Yarrawonga in 1950 and over-running billabong habitats down to Mildura. In 1967 it was “…common in the Lachlan River just above its confluence with the Murrumbidgee” but it hasn’t been recorded there for many decades.
Tench was last reported in the commercial fishery in the Lower Murray, Lower Darling and Murrumbidgee rivers in 1982, 1988 and 1980 respectively. Since the arrival of Carp, Tench has become rare in the Basin in SA (where it is <0.1% of the catch in the Eastern Mt Lofty Ranges) and rare or absent in NSW and is not present in the ACT and Qld. Prior to the arrival of Carp, it was suggested that Tench in Australia did not cohabit well with Redfin perch, but this was not confirmed.
In the sampling for the Sustainable Rivers Audit (2004–13), only 200 Tench were caught (<0.1% of all fish captured) and all were from Victoria (in the Campaspe (164), Loddon (34) Avoca and Wimmera (1 each) catchments). Of these, 104 were from upland sites (400–700 m elevation), 94 from slopes sites (200–400m) and only 2 from lowland sites (0–200 m). In the MDB Fish survey (2014/15-2021/22) a total of 24 were caught, all from the Campaspe uplands (17) and Loddon slopes (7) in Vic.
Brumley 1996; Cadwallader 1977; Cadwallader & Backhouse 1983; Clements 1988; Gilligan 2005a,b; Lake 1967; Merrick & Schmida 1984; Pompei et al. 2012; Rowe et al. 2008; Rowland 2020; Weatherley 1959, 1962; Weatherley & Lake 1967; Whiterod et al. 2015.
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