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
, or the percula clownfish (Amphiprion
)—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.

"Releasing non-native reef fish is like playing Russian roulette with tropical marine ecosystems," said marine biologist Brice Semmens of the University of Washington in Seattle. Semmens is lead researcher behind the recent survey, which detailed 16 non-native tropical species found off the coast of Florida.

Plants can pose a significant threat too. The fast-spreading seaweed Caulerpa taxifolia—dubbed killer algae—is a popular aquarium species. Since the 1980s it has rapidly invaded much of the Mediterranean coastline and also cost many millions of dollars in eradication efforts in California waters.

Beyond Ballast

Despite the potential threat to ecosystems, the aquarium industry has received little attention from authorities and experts as an important source of invasive marine species. Most attention to date has focused on ballast water from the shipping industry as the main source.

Ballast water is carried in a ship's hold for increased stability. A ship may take on ballast water (and the fish in it) in one region and later eject that water into a different region.

Legislation in place in the U.S. to protect against invasive aquatic species was created as a direct response to the invasion of the zebra mussel into the Great Lakes, Padilla said.

"This invasion brought the problem of aquatic invasives to the forefront, and because it was the result of ballast water and shipping, that has been the focus of attention," she said.

The survey led by the University of Washington's Semmens—published in a January issue of the science journal Marine Ecology Progress Series—adds to the evidence that introduced marine species are coming from the aquarium industry.

His team found no correlation between the origins of non-native marine fish spotted off the coast of Florida since 1999 and shipping routes to the region. Instead they found that commonly observed species—such as the emperor angelfish, the yellow tang (Zebrasoma flavescens) and the orbicular batfish (Platax orbicularis)—are all very popular with marine aquarium hobbyists.

"Although there has been anecdotal information about aquarium release as an important [source of] aquatic invasion, unfortunately there has been little scientific evidence for most species," commented the State University of New York's Padilla. More studies like this will help fill in those gaps and draw attention to the problem, she said.

And that problem is already large. A third of the aquatic species on the World Conservation Union's list of top hundred worst invaders are aquarium species or pond plants.

Stemming the Flow

The first step in helping to slow the spread of plants and animals from the aquarium trade is educating people about risks and problems associated with the introduction of unwanted species, Padilla said.

The next step might be to develop a certification system to make it clear which species are at low risk of invading.

The public can play a significant role in preventing the invasion of exotic species by not dumping their aquariums into natural waters in the first place, added Padilla's co-author, environmental scientist Susan Williams of the University of California Davis. "If they don't want their setup, they can return the contents to some pet stores, [can go] to the local department of fish and game or natural resources, or humanely kill the organisms by freezing them," Williams said.

The aquarium industry can assist by labeling products with cautions about the risks of releasing aquarium species. "These measures might be sufficient to make regulation of the industry unnecessary," she said.

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