OLYMPIA - Property owners should avoid introducing fish to backyard ponds in their efforts to eliminate mosquito-breeding areas and stem the expected spread of West Nile virus.
Artificially introducing fish or amphibians is not the most effective way to control mosquitoes in pools and ponds, and could pose a long-term threat to some of Washington's native species by preying upon them, competing for food or spreading disease, say Washington Department of Fish and Wildlife (WDFW) biologists.
State law prohibits importing or releasing certain fish and wildlife species known to have a damaging effect on native species, and requires a state permit for release of other species into large ponds or pools.
"We recognize and share citizens' concern over West Nile virus, but there are other ways to reduce mosquito-breeding areas without potentially inflicting long-term harm on the state's native wildlife," said Scott Smith, WDFW's aquatic nuisance species coordinator.
Better alternatives for private property owners include aerating ponds with underwater pumps to keep water moving, cleaning small water features weekly and planting areas surrounding pools with native vegetation that attracts mosquito-eating birds.
In addition, property owners can effectively control mosquitoes by draining and cleaning up other easily overlooked water-collecting objects such as clogged gutters, old tires, empty flowerpots, buckets, wheelbarrows and plant saucers.
It is permissible to purchase and release fish commonly available in pet stores into small, contained backyard water displays, but they should not be released into larger bodies of water or into partially contained water that may occasionally flood into natural water bodies.
Citizens who seek to import or transfer any live fish into large ponds or open waters are required to first obtain a stocking permit from WDFW. More information on stocking permits is available at WDFW regional offices in Spokane, Ephrata, Yakima, Mill Creek, Vancouver and Montesano.
With news stories circulating on the anticipated spread of West Nile virus this year, some sources have suggested introducing so-called "mosquito fish," the common name for gambusia. However, gambusia, a small minnow-size fish native to the southeastern United States, is among the species prohibited for importation or release, except by public health agencies, because of the threat it poses to the native ecosystem.
Some amphibians also are banned because of the serious risk they pose to native fish and wildlife. Bullfrogs, for example, are voracious non-native predators that gobble other frogs, small fish and even juvenile western pond turtles, a species the state is attempting to recover from the brink of extinction.
"If people introduce these species they can introduce a pest that can harm our native wildlife and cause enormous economic damage," said Smith.
The following are prohibited aquatic animal species under state law:
- African clawed frog (Xenopus laevis)
- Bull frog (Rana catesbeiana)
- Fish hook water flea (Cercopagis pengoi)
- Spiny water flea, (Bythotrephes cederstroemi)
- Mitten crabs (All members of the genus Erochier)
- Red swamp crawfish (Procambarus clarkii)
- Rusty crawfish (Orconectes rusticus)
- European green crab (Carcinus maenas)
- Bowfin, grinnel or mudfish (Amia calva)
- China fish, snakeheads (All members of the genus Channa)
- Piranha: (All Pygocentrus, Rooseveltia, and Serrasalmus)
- Walking catfish
- Fathead minnow (Pimephales promelas)
- Grass carp in the diploid form (Ctenopharyngodon idella)
- Ide, silver orfe or golden orfe (Leuciscus idus)
- Rudd (Scardinius erythropthalmus)
- Round goby (Neogobius melanostomus)
- Northern pike (Esox lucius)
- Zebra mussels: (Dreissena and all species known as quagga)
- New Zealand mud snail (Potamopyrgus antipodarum)
- Nutria (Myocastor coypu)
For more information on the state law governing unlawful use of prohibited aquatic animal species see RCW 77.15.253. For the law classifying nonnative prohibited animal species, including prohibited animal species see WAC 220-12-090.