Two-spined Blackfish

Photo of Two-spined Blackfish

Two-spined Blackfish. Photo: Mark Jekabsons, ACT Government.

The Two-spined Blackfish (Gadopsis bispinosus) was declared a vulnerable species in the ACT in 1997 and risks of further population decline are possible unless active steps are taken to protect and maintain its habitat.

The fish is found in the cooler, upper reaches of the Murray–Darling river system in Victoria, New South Wales and the Australian Capital Territory. In the ACT, it is only found in the Cotter River upstream of the Cotter Reservoir.

The Two-spined Blackfish is known for its yellowish-brown to olive green colouring and spectacular dark brown ‘giraffe’ spots often with white edges to its fins, which help it blend in with its surroundings. Adult fish are less than 30 centimetres long and weigh 200 grams or less.

It requires cool clear streams with boulders and cobble for shelter, and some upland reservoirs. Fish rarely venture more than 25 metres from home and adults are usually only active from dusk to dawn. Their diet consists of aquatic insect larvae, mayflies, caddisflies, midges and terrestrial invertebrates.

Two-spined Blackfish can live for eight years. Females start breeding from about two years old, laying up to 240 eggs a year in a single mass in spaces between cobbles and boulders or attached to rocks.

Conservation threats

The major threats to Two-spined Blackfish are habitat destruction or modification, river regulation, barriers to fish passage, sedimentation, reduced water quality, alien fish species and climate change.

Sedimentation is a particular threat because these fish lay eggs on rocks, shelter within the rocks and usually feed on bottom-dwelling invertebrates. In the past, sedimentation of streams from forestry practices and following fires has filled pools and smothered spawning sites, removing shelter food supply.

The remaining ACT population in the Cotter River has been fragmented by the construction of dams and river crossings. Dams have flooded riverine habitats and changed flows.

Alien fish species including Rainbow Trout and Brown Trout, Oriental Weatherloach and Eastern Gambusia impact on Two-spined Blackfish by competing for food and habitat, predation, introduction and spread of and parasites and disease.

Given fish can’t regulate their body temperature or easily escape unsuitable habitat conditions, they are highly vulnerable to the impacts of climate change. Climate change is predicted to result in drier, warmer conditions and higher intensity rainfall and bushfires, which is likely to result in increased sedimentation, impact spawning sites from high flow and  alter the fish’s spawning cues.

Conservation actions

The ACT Government proposes to maintain, in the long term, a viable, wild population the Two-spined Blackfish. These actions will be driven by the Two-spined Blackfish Action Plan (2018) and the ACT Aquatic and Riparian Conservation Strategy (2018).

Conservation actions that have already been introduced, including:

  • Fishing prohibition since 1997
  • Annual monitoring of populations to inform species management decisions
  • Environmental flows for the Cotter River to maintain populations and improve breeding success
  • Revegetation in the Lower Cotter Catchment with native plants and the reduction of forestry roads which has reduced sediment getting to the lower Cotter River.

Conservation actions will focus on:

  • protecting sites in the ACT where the species occurs, the Cotter River and associated reservoirs
  • managing habitat to conserve the populations, particularly through minimising sedimentation and managing the riparian zone so it continues to contribute organic material for food and provide shade to buffer water temperatures
  • managing alien fish species, connectivity, stream flows and sedimentation in habitats known to support existing populations
  • where possible, increasing habitat area and/or better connecting populations
  • improving understanding of the species’ ecology, habitat and threats through survey, monitoring and research
  • improving community awareness and support for Two-spined Blackfish and freshwater fish conservation in general.

More information

Contact or Canberra Connect 13 22 81