A tiny fish in Tasmania might be in trouble. These tiny fish, swan galaxias, can grow to a maximum length of about 5 inches. The Threatened Species Scientific Committee, an advisory body to the Australian government, states that the primary threat to this fish is competition and predation from alien fish. The introduction of brown trout to the island more than 160 years ago is a major culprit.
How trout arrived
Settlers made early, scattered attempts to introduce trout and salmon to the territory starting around 1841, but the breakthrough came in 1864, when trout eggs brought across the ocean from England were successfully hatched at Plenty, Tasmania. Eventually, trout became widespread around the island's rivers and lakes. But now there was a new danger for the tiny native fish of Tasmania, who found themselves sharing their streams with a new predator.
A small fish under pressure
The swan galaxias is a small, robust, freshwater fish. It lives only in eastern Tasmania, and feeds on insects and small crustaceans. Since 2000, it has been listed as endangered in Australia. The committee says healthy populations survive only in stream sections protected from trout by a natural barrier, such as a waterfall or marsh. However, in cases where either the trout or redfin perch have been found, there has been local extinction, according to the committee, which believes that these fish cannot coexist with the brown trout. The committee also notes that researchers still need to confirm exactly why those fish disappeared.
A broader pattern
Tasmania is not alone with this problem. Fish scientist R. M. McDowall reviewed galaxioid fishes across the cool southern hemisphere. His 2006 paper published in Reviews in Fish Biology and Fisheries found that these fishes mostly declined dramatically where brown and rainbow trout were introduced. There were some exceptions. He also mentioned other problems such as habitat degradation. Nevertheless, he concluded that these fishes are among the most seriously threatened fishes known.
Building safe havens
{{/usCountry}}Tasmania is not alone with this problem. Fish scientist R. M. McDowall reviewed galaxioid fishes across the cool southern hemisphere. His 2006 paper published in Reviews in Fish Biology and Fisheries found that these fishes mostly declined dramatically where brown and rainbow trout were introduced. There were some exceptions. He also mentioned other problems such as habitat degradation. Nevertheless, he concluded that these fishes are among the most seriously threatened fishes known.
Building safe havens
{{/usCountry}}If trout are impossible to keep out of a stream, one idea might be to move the fish. Between 1989 and 1995, swan galaxias were moved into several fish-free streams that alien fish could not reach. The streams are located in six river catchments, in the natural habitat of the fish. The idea was simple: give the fish places trout cannot reach. Today, this idea is used by conservationists who establish trout-free refuges. The committee's recommendations also include stopping trout stocking in catchments where the fish lives, building trout barriers, and enforcing the ban on using swan galaxias as bait.
Open questions
Moving fish around might not be the perfect fix. The committee noted that the natural genetic variety of the moved groups was unknown. Genetic diversity enables a species to adapt to change. The natural populations are also isolated from one another. So the 2016 advice called for further genetic studies. When the advice was written in 2016, the fish's eggs had not been found in the wild, so its spawning sites were still a mystery.
A big lesson
Trout are popular with many anglers, and this story is not about blaming anyone. A single decision made in a different century still shapes which Tasmanian streams can support this fish today. There are thought to be only around 6,000 swan galaxias left. Every troutless stream offers these tiny fish one more home. Protecting a few small, trout-free streams might be a way to help a fish that most people will never see.