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Brown trout (Salmo trutta)

Brown trout were introduced to Australia for fisheries and angling and are now established in waterways. They can prey on and compete with native species, including freshwater animals of conservation concern.

Key facts

Type: Pest animal, fish.

Native to: Europe, northern Africa and western Asia.

Established in: NSW, ACT, VIC, TAS, SA.

Other names: sea trout, sea-run trout, finnock, sewin.

Best time to act: Survey and target adults in autumn and winter, when mature fish may move into rivers to spawn.

Identification

  • The body is streamlined, usually brown or golden-brown, with a small pointed head and a large mouth that extends beyond the eye.
  • Dark spots, often surrounded by pale halos, occur on the body above and below the lateral line.
  • River fish may have orange sides and a pale belly; sea-run fish are more silvery and their spots are less visible.
  • The small adipose fin has a red margin, and young fish have dark vertical parr marks along their sides.
  • Look-alike: Rainbow trout also have spots, but typically have rows of black spots on the tail; Atlantic salmon lack the red margin on the adipose fin.

Where it lives

In Australia, brown trout live in freshwater streams, rivers, lakes and reservoirs, and may also use estuaries and coastal waters.

Why it matters

  • They prey on native fish and other aquatic animals and compete with native fish for food and habitat.
  • Introductions have been associated with impacts on freshwater biodiversity in Australia, including possible declines of the Tasmanian mountain shrimp and reductions in aquatic insect groups in Victorian streams.
  • Brown trout can carry parasites and diseases that affect fish.

How it spreads

  • They were deliberately introduced to Australia for fisheries and angling, and have been established through natural reproduction.
  • Fish can move through connected waterways; sea-run trout migrate between coastal waters and freshwater rivers to spawn.
  • Avoid releasing or transferring live fish, water or fish-bearing equipment between waterways.

Control methods

  • Plan control with the relevant state or territory fisheries or biosecurity authority, and check which methods are approved for the site.
  • Use targeted capture and removal, such as angling or authorised netting, where appropriate.
  • Repeat surveys and removal because fish may remain after an initial effort; monitor connected waters for further spread.
  • Report suspected new populations or significant impacts to the relevant state or territory agency, and do not move or release captured fish.

Site hygiene and welfare

  • Clean, drain and dry boats, nets, waders, footwear and other wet equipment before moving between waterways.
  • Do not carry live fish or untreated water between sites; remove plant material, mud and other debris from gear.
  • Use methods set out in the national model codes of practice and standard operating procedures for the species.
  • Coordinate control with neighbours and the local government biosecurity plan, as isolated effort is quickly undone by reinvasion.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: General biosecurity duty. Not prohibited matter in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not a declared pest. Not a declared pest or prohibited matter in Tasmania. Importing animals is still controlled by Biosecurity Tasmania.
  • Northern Territory: Not a declared pest. Not on an NT declared or prohibited list. Check with the NT Government before keeping, moving or releasing it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board

Sources