In a worrying development this month, scientists at the Florida Keys National Marine Sanctuary found a pair of orbicular batfish, a popular aquarium fish endemic to the Pacific Ocean.
The fish were captured to stop them breeding and competing with local fish. The move follows increasing sightings of exotic species not native to the area, including popular aquarium fish such as orangespine unicorn fish, raccoon butterfly fish, several varieties of tang and angel fish, and the predatory lionfish.
All come from the west Pacific, the north-west Indian Ocean and the Red Sea, yet they have been seen at 32 sites off Florida. "It's a Finding Nemo story," says Brice Semmens, a marine biologist at the University of Washington, Seattle. "Individuals are releasing their pet fish with the best of intentions, but in the wrong ocean. It is a really bad idea."
The aquarium trade has long been suspected of introducing alien species, but the link has never been proved. So a team led by Semmens compared figures from imports of tropical marine fish into the US with sightings of exotic fish in the wild recorded by REEF, a non-governmental organisation, between 1993 and 2002.
Statistical analyses on random samples confirmed that fish species imported in the highest numbers are those mostly likely to have been sighted off the US coast. The researchers ruled out the ballast water picked up and discarded by ships to maintain stability as a cause for the introduction of exotic fish. "Their home ranges do not overlap with shipping routes," Semmens says. Most of the exotic fish have yet to establish a viable population, but scientists are worried about the ecological and economic impact of the increasing numbers of lionfish.
Once found at only three sites in Florida, this highly venomous fish has recently been seen in waters from North Carolina to New York. In their native habitat, lionfish prey on a wide variety of fish, shrimps and crabs. "Introduction of the lionfish is an ecological quantum leap for local fishes that have no experience dealing with this voracious predator," Semmens says.
Walter Courtenay, a research fishery biologist with the US Geological Survey, suspects that dive boat captains hoping to attract more customers were more likely at fault than pet owners. But biologists agree that now the fish is established, it may be impossible to eradicate.
In the coming weeks, the US National Oceanic & Atmospheric Administration and representatives from the aquarium industry will join forces to educate the public about the dangers of dumping pet fish into the ocean. Congress is also considering setting up screening for fish imported by the aquarium trade, by extending legislation aimed at preventing the introduction of invasive species via ballast water.
Author: Amitabh Avasthi
This article appears in New Scientist issue: 3 JULY 2004.
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