In 1864, Tasmania imported brown trout for sport. 162 years later, it is building barriers to save a native fish reduced to just 6,000 individuals

For more than a century, an introduced fish has been reshaping Tasmania’s freshwater ecosystems. Now, conservation teams are building artificial barriers, clearing waterways and creating isolated refuges in an effort to prevent one of the island’s native fish from disappearing completely.

The Swan galaxias, a small freshwater fish found only in eastern Tasmania, is estimated to number about 6,000 individuals. Much of its former habitat has been lost after introduced brown trout spread through the island’s river systems, leaving the native fish largely confined to small headwater streams that trout have difficulty reaching.

An introduction that changed Tasmania’s rivers

The story began in 1864, when European brown trout eggs were brought to Tasmania from England. The introduction was considered a major success for recreational fishing, and trout eventually became an important part of Tasmania’s fly-fishing culture and regional tourism.


But the ecological consequences were significant. Brown trout spread through freshwater systems across the island, where they preyed on smaller native galaxias and competed with them for food and habitat. Over time, populations of Swan galaxias disappeared from the lower and middle sections of their former river range.

Species assessment data from the Tasmanian government's Threatened Species Link portal indicates that the fish was pushed into small, separated headwater streams in the Swan and Macquarie River catchments.

Waterfalls became a natural line of defense

The Swan galaxias grows to only around 10 to 13 centimetres long and, unlike invasive salmonid fish, has limited ability to jump. That characteristic has contributed to its survival in some remote upper streams, because natural barriers such as waterfalls can prevent brown trout from moving farther upstream.

One such refuge is protected by Hardings Falls. These natural barriers have effectively created pockets where Swan galaxias populations can survive without constant predation from trout.

However, isolation also creates a vulnerability. Droughts, floods and other disturbances can damage these small habitats, potentially wiping out an entire population. With the species already restricted to fragmented streams, the loss of even a few remaining populations could have serious consequences for its long-term survival.

Building barriers to keep trout out

Conservation workers are now attempting to strengthen these natural defenses. Fisheries officers and scientists have spent years studying Tasmania’s stream networks to identify locations where specially designed barriers can prevent brown trout from moving into important Swan galaxias habitat.

The barriers are intended to create sections of stream that remain inaccessible to trout while allowing the native fish to continue breeding. Where trout manage to cross into protected areas, field teams can use targeted electrofishing to locate and remove them.

The process is demanding because simply constructing a barrier does not guarantee that an isolated population will remain secure. Teams must repeatedly monitor the waterways and respond when invasive fish breach the protected areas.

Creating new populations in trout-free streams

Once a section of habitat has been confirmed to be free of brown trout, conservationists can introduce small groups of Swan galaxias from healthier populations.

The strategy is designed to spread the species across a larger number of protected locations rather than relying on a handful of surviving populations. Nine translocated populations have now been established in eastern Tasmania, including at Upper Blue Tier Creek, Rocka Rivulet and Green Tier Creek.

These new populations act as additional safeguards. If a natural disaster or disease affects one isolated group, other populations can potentially survive elsewhere.

Protecting native fish without ending trout fishing

The conservation program presents a particular challenge because brown trout are deeply established in Tasmania and recreational trout fishing remains an important part of the island’s outdoor culture and regional economy.

Fisheries managers therefore distinguish between established recreational fishing waters and the small headwater tributaries being protected for the Swan galaxias. The conservation work is concentrated on upper tributaries and isolated streams that have little or no significance for sport fishing but are highly valuable as refuges for native wildlife.

The approach is consequently less about removing trout from Tasmania’s entire freshwater network and more about creating carefully selected areas where an endangered native species can survive without the pressure of an introduced predator.

A small fish facing a much larger legacy

The Swan galaxias illustrates how the ecological consequences of an introduction can persist for generations. What began in the 19th century as an effort to establish a popular sport fish has contributed to major changes in Tasmania’s freshwater communities.

Today, the survival of the Swan galaxias depends partly on keeping certain streams beyond the reach of brown trout. Conservationists are combining natural waterfalls with engineered barriers, invasive-fish removal and carefully planned translocations to create a network of trout-free refuges.

For a species now confined largely to isolated headwaters, these protected streams may represent its best remaining defense against extinction.