Leonie Joubert explains how the story of an alien goldfish in Cape Town reminds us of how poorly the country has dealt with the invasion of alien vegetation.

This is a story about a goldfish – let’s call him Jimmy – and the good intentions of the guy who set him free. Mostly, it’s about how Jimmy – flashy, fan-tailed, ethereally floating Jimmy – was about as desirable in his new “wild” home as an oil slick or a shredded plastic bag tangled up in barbed wire. Because when Jimmy’s owner decided to free him into a pond on Table Mountain, the guy may as well have been dumping rubbish.

Jimmy is an alien. And outside of his “natural” home in a fish tank, he is pollution. Jimmy achieved regional fame for all of a week, when the managers of Table Mountain National Park decided to remove him from the World Heritage Site to a pond somewhere in the Cape Town suburbs. He was one of several goldfish in the mountain water course, whose owners could not keep them but didn’t have the heart to flush them into the sewer. So they did what they thought was the honourable thing and set the fish free, into the wild.

There was a small but vociferous public outcry voiced mostly on a local talk radio station, protesting the “right” of these fish to stay in their new mountain home. Nature conservationists said no, the fish were alien and had to go. The truth is that Jimmy and his mates are something of a caricature in one of the most under-played but serious environmental issues facing us today. After loss of habitat, the second greatest threat to species and their natural spaces is that of invasive aliens.

They pollute the environment in a way which is more subtle than piles of stinking litter or a sky clogged with filthy smoke. Nevertheless, invasive species cost the global economy about $1,4 trillion every year – the equivalent of five percent of the global GDP – through damage to crops, pastures and forests. Invasive species undermine biological diversity and alter ecosystems’ ability to function and sustain life, eroding resources such as food, shelter or water. A collapsed natural system is also less likely to work as a “sink” to absorb sewage, biodegradable waste and other pollution associated with human settlement.

In South Africa, plant invaders are the most visible form of biological pollution. In the 350 years since Europeans settled here, approximately 8 750 exotic plants have been introduced, mostly for food, fodder, timber and garden decoration. Most have stayed within the confines of domestication, but another 180 have managed to spread across more than 10 million hectares of countryside. They pollute the soils with added nutrients, change fire regimes, undermine agriculture and drink more than their share of water.

Jimmy’s story ended happily – he and his pals were settled in a pond near Newlands Forest and any potential threat of them spreading unchecked in that Table Mountain water course was curbed. If conditions had been as favourable for this fish as they have been for plants – such as the black wattle or ubiquitous rooikrans – when they were first introduced to the country, the story could have ended very differently indeed.