A medium sized fish, similar in body shape to the Rainbow trout but lacking the fine, black spotting on the tail and the pink stripe on the sides. Maximum weight is 20 kg; commonly 1–4 kg. Large spots present on the back and sides, but not on the tail, and adipose fin with an orange rear-edge. Spots on the back are usually dark and those on the sides are either dark or reddish-orange surrounded by a light halo.
Brown trout is found in cool upland streams and lakes. The diet contains a wide variety of freshwater insect larvae, snails and wind-blown terrestrial arthropods, aquatic crustaceans, and small fish. Brown trout become increasingly piscivorous as they grow, with the diet of fish >250 mm length in the Canberra region having increasing proportions of fish.
Spawning occurs between April and August, earlier than Rainbow trout. Similar to Rainbow trout, eggs are deposited in a gravel nest (‘redd’) constructed by the female in flowing water. The eggs are large (4–5 mm diameter) and hatch in 6–20 weeks depending on water temperature. Brown trout is slightly less tolerant than Rainbow trout of warm water, preferring temperatures below 25°C.
Brown trout is often found with the parasitic copepod Lernaea cyprinacea (anchor worm) attached, particularly around the fins. It is generally a longer-lived species than Rainbow trout, often surviving to six years of age, although individuals have been recorded in excess of 25 years of age overseas.
Brown trout forms the basis of important recreational fisheries in southeastern Australia and is widely stocked. However, in light of its serious impact on a number of threatened native fish, particularly galaxiid species, stocking is no longer allowed in a number of streams and dams where threatened species are known to be present.
As with Rainbow trout, Brown trout has had a serious impact on the distribution and abundance of south-east Australia’s native galaxiids, with many threatened galaxias species now confined to small sections of headwater streams above barriers to trout invasion. Nine of 14 newly described galaxiid species have been recently listed as critically endangered, with all of these species threatened by trout.
Significantly, it is highly likely that trout have caused the extinction of several additional galaxias species before they could be discovered. In the Basin trout have seriously reduced the abundance and distribution of Mountain galaxias, the threatened Barred galaxias and Stocky galaxias. Brown trout is suspected of having deleterious impacts on Trout cod and Macquarie perch and a number of other threatened native species such as Two-spined blackfish and Southern pygmy perch. Brown trout regularly prey on Two-spined blackfish (of all sizes) in the Cotter River. A 430 mm Brown trout containing three Macquarie perch (110-140 mm length) in its stomach was collected from Cotter Reservoir in 2018. The trout choked on the largest of the 3 fish! Trout species also impact a number of threatened frogs, such as the Spotted tree frog (Litoria spenceri) and are prolific predators of spiny crayfish (Euastacus spp.) in the uplands. Brown trout is listed in the 100 world's worst invasive alien species by the IUCN.
Brown trout is native to Europe and western Asia. It was first introduced to Australia in 1864 (after several failed attempts) when 1200 eggs (along with 100,000 Atlantic salmon eggs) packed in 181 boxes with moss and 32 tons of ice was transported from England to Melbourne on the ship Norfolk. Upon arrival in Melbourne (after 84 days at sea), all the trout eggs and the majority of salmon eggs were then transported to Hobart, and subsequently hatched and released into the Plenty River. Subsequently Brown trout were then distributed throughout Tas, and introduced to Vic (1866), NSW (1869-81), WA (1974), SA (1879) and Qld (~1880s).
During the Millennium Drought Brown trout abundance declined significantly as small streams warmed or dried and widespread bushfires affected many catchments. For example Brown trout disappeared completely from a number of streams in the ACT, and recolonization following the breaking of the drought in 2010 was slow, but is accelerating. Fisheries agencies in the Basin have substantial stocking programs for this and other trout species. Vic and NSW fisheries agencies release approximately one million Brown trout each year; and private hatcheries also make releases. Brown trout is widely distributed in the cooler upland streams of Vic, NSW and the ACT, as well as a small number of streams in SA. It is not present in Qld. There is a tendency for Brown trout to become the dominant species in lakes and dams where both Rainbow and Brown trout are present.
A total of 3139 individuals were recorded in the Sustainable Rivers Audit (2004–2013) from 16 river valleys, with 40%, 33% and 26% from upland, montane and slopes elevational zones respectively. The MDB Fish Survey (2014/15–2021/22) recorded 1442 individuals from 9 river valleys.
Birnie-Gauvin et al. 2019; Cadwallader 1996; Clements 1988; Davies & McDowall 1996; Ebner et al. 2007a; Gillespie 2001; Healy et al. 2020; Jackson et al. 2004; Jackson & Williams 1980; Jarvis et al. 2019; Lintermans 2013b; Lintermans et al. 2020; Lowe et al. 2000; McDowall 2003, 2006; Raadik 2014; Tilzey 1976.
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