Freed Pet Fish Threaten Native Species, Study Says

John Pickrell
for National Geographic News
June 1, 2004

The aquarium fish industry is worth hundreds of millions of dollars a year worldwide and is growing rapidly. Much of this money flows into developing countries where the majority of popular tropical marine species—such as the emperor angelfish (Pomancanthus imperator), or the percula clownfish (Amphiprion percula)—are found.

Various organizations, including the United Nations, have promoted regulated harvesting of ornamental fish for export, as a method of sustainably managing marine ecosystems and bringing wealth to some of the world's poorer regions.

However, some experts now argue that though the aquarium industry could help preserve ecosystems in developing nations, the same industry poses a growing threat to wildlife elsewhere, if aquarium fish are later released into the wild.

The escape of marine species from the aquarium industry is only beginning to be recognized as an important problem in countries such as Australia, New Zealand, and the United States.

Earlier this year, a survey revealed that 16 species of non-native tropical fish have been found at 32 locations along the southeast coast of Florida—all most likely introduced when hobbyists freed aquarium fish into the ocean.

Environmental Cost

"There has been a large push to encourage development of the aquarium and ornamental [aquatic species] trade, viewed as a green industry, a possible solution to saving wild populations, and a means to increase the revenues of developing countries," said Dianna Padilla, conservation biologist at the State University of New York in Stony Brook.

"However, to date the environmental cost of escapees has not been figured into that equation," said Padilla, co-author of another report exposing the problem in a recent issue of the science journal Frontiers in Ecology and the Environment.

Introduced species of fish can harm ecosystems in a number of ways. They can compete with native species for resources, potentially driving them toward extinction and can also alter habitats in ways that are damaging to native fish. Catfish, for example, disrupt vegetation and alter shorelines, making them uninhabitable for other fish, Padilla said.

Immigrant fish can also carry exotic diseases or can be aggressive predators that threaten native populations directly. China's carnivorous northern snakehead fish (Channa argus), which grows up to three feet (one meter) in length, has preyed upon native fish and amphibians in a number of U.S. states, including Maryland and now Virginia, where its discovery has caused much alarm in recent weeks. The aquarium industry is already recognized as a source of freshwater invasive species such as the snakehead.

Some species, such as the lionfish (Pterois volitans) now found off the southeastern coast of the U.S., have poisonous spines and even pose a threat to people.

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