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Warning against freeing pet fish

Guppy
Image caption Guppies could establish populations even when no males were present

The release of a single female pet fish into the wild can generate entire new populations, even with no males present, according to new research.

A new study has revealed how the guppy's ability to keep on reproducing has earned the fish its reputation as one of the world's most invasive fish.

St Andrews University biologists, who made the discovery, are now warning pet owners against releasing the fish.

West Indies University experts also worked on the study.

The biologists have confirmed the two most important routes of guppies finding their way into the wild are the escapes of ornamental fish, and deliberate introductions designed to control the larvae of mosquitoes that spread malaria.

In places such as Southern India, guppies are routinely released into water troughs, wells and small ponds for mosquito control.

Although self-contained at first, heavy rains and flooding mean that the fish eventually find their way to streams and rivers where they come into contact with native fish.

Dr Amy Deacon, St Andrews University lead researcher, said: "Usually only one or a few fish are released.

"We know that the vast majority of species introduced to a new habitat in this way are unable to survive, let alone establish a population, which left us with a huge question mark."

To try to solve the mystery, the researchers conducted an experiment where single wild female guppies were put into outdoor tanks.

After two years, they discovered that almost all of the tanks contained populations of guppies, each founded by just one female.

Reduced biodiversity

Dr Deacon said: "Sperm storage is an excellent adaptation for living in constantly changing habitats, and it might also explain the guppies' global success.

"Female guppies can store sperm in their reproductive tracts for many months after mating, and this enables single fish to establish populations, even when no males are present.

"We also found that these populations kept all of the important behaviours that wild guppies have, so they would be well-equipped for surviving in a new environment."

"Our study shows why we should be cautious when releasing exotic species.

"Seemingly harmless activities such as a child freeing a few pet fish or a concerned householder using guppies to control mosquitoes, can ultimately contribute to the reduction of biodiversity in freshwater habitats across the world."

The popular ornamental fish, whose native home is Trinidad and the north-eastern fringe of South America, is now present in more than 70 countries worldwide.

The research, published by the journal PLoS ONE, was funded by the Natural Environment Research Council and the European Research Council.

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