Last Friday, the U.S. Fish and Wildlife Service declared illegal the importation and interstate transportation of live snakehead fish or their eggs in response to growing concerns that the predatory fish, native to southeastern Asia, poses significant risk to the fish and wildlife populations of the United States.
In July, nearly 100 juvenile northern snakehead fish were found in a pond in Crofton, Md. after the pond's owner mistakenly dumped a male and female snakehead in it by mistake.
Additionally, four species of snakeheads, including the blotched, bullseye, giant and northern varieties, have been found in California, Florida, Hawaii, Maine, Maryland, Massachusetts and Rhode Island. Only Florida, Hawaii and Maryland are known to have reproducing populations.
The fertility rate is high in large snakehead species. The northern snakehead can produce up to 51,000 unfertilized eggs while the bullseye snakehead can produce as many as 40,000.
Adult northern snakeheads are carnivorous, and feed on frogs, aquatic birds, baby turtles, small mammals and other fish including native predatory fish.
"Since all snakehead species are piscivorous [that is, they eat fish], they all have the potential to disrupt the balance of fish communities in U.S. waters if their numbers get out of control," said William Rickards, environmental science professor and director of the Virginia Sea Grant Program.
Because of the threat to the native fish population, Maryland Fishery Services took action early last month to eradicate the potentially injurious species by poisoning the Maryland pond where the first snakeheads were found.
"If a newly introduced species is found in a situation such as an isolated pond, it is best to kill it as soon as possible before it escapes or someone introduces it elsewhere," said Walter Courtenay, a biologist at Florida Carribean Science Center.
"Once a species is no longer in a confined habitat, such as the northern snakehead now is in the St. Johns River of Florida, it's too late to eliminate it. We can only hope that people won't move them to other waters. A big education process is needed," he added.
Unlike normal fish, snakeheads breathe air, and can survive out of water for up to seven days according to Courtenay.
Two chambers in front of their gills enable them to gulp air at the surface and remove oxygen from the air as long as their gills remain moist. Some species can secrete mucus that helps to maintain moisture. By instinct, some species are capable of overland travel by wriggling motion -- deserting dried-out habitats in search of those with water.
"Long-term, long distance movement across dry land is not likely, but they can survive out of water as long as they can stay moist via rain and dew,"Rickards said.
Warm climate is the most important environmental factor that could determine the potential spread of snakeheads in the United States. Most species of snakeheads are native to subtropical or tropical climates and can thrive only in places such as southern Florida, southern Texas, Hawaii and warm springs in the desert southwest. Several others, however, can tolerate cooler temperature conditions and could survive the winter in most of the southern states.
The superb tolerance and adaptability of snakeheads to different environmental conditions aided their establishment in U.S. waters. They also are the top predators in their native ranges, meaning that no other creatures feed on adult snakeheads.
But there are fish species that feed on enough juvenile snakeheads to keep their populations from getting too large. Snakeheads also eat their own young when there is no other food available.
Some anglers' organizations suggested that only five species of snakeheads be banned from importation and interstate transportation. Courtenay said that law enforcement would be a problem in this case.
"Identifying snakeheads from other families of fish is easy, but not different species of snakeheads. We have to ban all of them. We have to keep them all out," Courtenay said.
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