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Efforts to eradicate rainbow trout from Ecuadorian waters will begin later this year

Ecuador’s environmental ministry is preparing a plan to eliminate rainbow trout from the country’s high-elevation lakes and rivers and hopes to implement it later this year.

Rainbow trout were introduced to Ecuador in the 1920s.

The eradication program was prompted by the work of biologists at the University Indoamérica in Quito that concluded that the rainbow trout is one of the most destructive invasive species in Ecuador. The biologists first approached the government in 2016 about the problem and have been consulting on methods to rid the country’s water systems of the trout ever since.

Introduced from North America to Ecuador in the 1920s, the rainbow trout is common today in the rivers and lakes of the country’s sierra region, most prominently in Cajas National Park west of Cuenca. It has also spawned a small industry of commercial production and the fish is widely available in stores and roadside stands.

The problem, according to Juan Manuel Guaya, an evolutionary biologist at Indoamérica, is that trout are wreaking havoc on other aquatic species and are responsible for killing off some. “They threaten native species in highland water ecosystems and the effect has been devastating in some systems,” he says. “Trout are not only a predator but they transmit deadly pathogens to other fish and amphibians.”

Guaya’s research shows that the presence of trout have almost eliminated several species of frogs in the Andes and upper Amazon basin, including the glass frog (Nymphargus grandisonae) and the Amazon bullanguero sapito (Engystomops petersi).

The trout have changed the behavior of tadpoles, Guaya says. “They have adapted to swim faster to avoid the trout and many die due to stress from chemical signals emitted by the trout.” He added that frogs that develop from the tadpoles often have birth defects. The study also shows that diseases transmitted by trout cause death rates as high as 80% in amphibian embryos.

Guayas and his team are working with the Ecuador Ministry of Agriculture, Livestock and Fisheries on ways to control the trout population. “It may not be possible to eliminate rainbow trout entirely from the ecosystem,” he says. “They are now in 125 countries of the world and they are hard to get rid of. The government will focus on national parks since it has control in these areas. With the means we have, it should be easier to eradicate them from high-altitude lakes and then we will move on to rivers and streams,” he said.

Guayas said that Cajas National Park near Cuenca will be the first target of the eradication program. He said he is working with biologists in Colorado, in the U.S., to identify natural pathogens as well as genetic methods to eliminate trout. The plan will be carried out by aerial spraying, he says.

A spokesman for the environmental ministry said that discussions will begin soon with commercial fisheries that grow rainbow trout in an effort to reduce the financial impact on affected growers.