Biological Taxonomy Domain: EukaryaKingdom: AnimaliaPhylum: ChordataClass: ActinopterygiiOrder: PerciformesFamily: ChannidaeSpecies: Channa argusCommon name: Northern Snakehead

Background & Environmental Constraints

Origin: China, eastern Russia, and the Korean peninsula

Speciation: Channa argus is 1 of 29 snakehead species

Temperament: AggressiveMaximum size: Up to 5 feet longWater parameters:

Freshwater pH: 6.0 - 7.5Temperature: 72-82˚ F (22-28˚C)

Threat to Biodiversity & EconomyThis top level predator fish is known to survive on land

and cause major strain on local ecosystemsAlter freshwater ecosystems by competing against native

fishReduce biodiversity through predation on aquatic and

terrestrial speciesCould push endangered or threatened species to the

brink of extinctionMay introduce fungal pathogen known as Epizootic

Ulcerative Syndrome (EUS) – infects foreign freshwater fish

Could damage commercial and recreational fishing industry in the Chesapeake by diminishing populations of fish that spawn in the Potomac River

Millions of dollars have been spent on fish stocking, dam modifications, and other projects to limit snakehead impact

Introduction to U.S. Waters In the past, Asian markets and other grocers were

allowed to import living snakeheads to the U.S. Over time, human beings introduced the species to

native waters First reported in U.S. waters in 1977 in Silverwood

Lake, California National Media debut in 2002

An angler caught an unfamiliar fish that measured 28 inches from a pond in Crofton, Maryland.

Took the picture to Maryland Dept. of Natural Resources where it was later identified.

After another fisherman caught spawning adult and baby snakeheads from the same pond, the national media disseminated the first stories of the snakehead.

To prevent the fish from migrating to the Potomac River, Maryland wildlife officials dumped the pesticide, Rotenone.

Killed all fish, including 6 adult and over 1000 snakehead young.

An unsuccessful effort as Channa argus appeared in the Potomac River 2 years later.

Northern Snakehead possesses competitive advantages that may allow it to out-compete native fish species

Primitive lungs Sacs above each gill that can fill with air and draw oxygen

from the stored air. Allows it to survive waters that are low in oxygen. Allows it to survive out of water for 2 – 3 days. Allows it to live under a sheet of ice

Aggressive Both parents guard the eggs and the fry Known to attack fishing lures.

Highly prolific Spawning females can release up to 15,000 eggs at a time Can mate up to 5 times per year. Equates to 75,000 offspring per year.

Indiscriminate feeders Feed on native fish, amphibians, crustaceans, birds, small

reptiles and small mammals. Snakehead video

Purpose:

In 2004, the VA Dept. of Game and Inland Fisheries initiated a study to monitor the snakehead’s expansion in the Potomac from 2004–2006.

Methods:

Surveyed on a monthly basis: Areas of known snakehead concentrations. Bodies of water contiguous but farther away to assess range.

Relative abundance of snakeheads was based on the number of fish retrieved per hour of electrofishing, and catches per unit effort of angling. Explanation of electrofishing

Sampled fish were separated into 8 groups, ages 0-7 (approximated based on size of sagittal otolith at necropsy). Accumulates in rings as it grows Used in age or growth studies

Counts of daily rings on sagittal otoliths of newborns (age-0) were used to estimate when fish hatched.

Data collection included total length (mm), weight (g), stomach content evaluation, gonad condition, and length at age. Stomach content evaluation entailed only removal and identification. Gonadosomatic indices (GSI) of ovary weight to body weight was used to

quantify spawning period.

Results:Table 1. Total number of northern snakeheads capturedfrom the Potomac River system, Virginia, during 2004-2006by use of several gear types (HL = hook and line; EP =electrofishing; BP = Backpack; other = dip net, trap net,seine, standing, and bow angling).

Year HL Boat EF BP EF Barge EF Other Total 2004 13 4 0 0 3

202005 11 59 127 71 3

271 2006 24 171 11 1 7

214 Total 48 234 138 72 13

505

Table 3. Length-at-age data (mm) for 167 northern

snakeheads sampled in the Potomac River system,Virginia, during 2004-2006 (all years combined).

Age N TL mean SD Min. Max. 0 9 133 23 88

166 1 18 190 20 155

227 2 24 287 85 163

480 3 53 357 85 218

588 4 39 431 100 308

669 5 17 545 111 362

674 6 4 578 52 531

634 7 3 560 9 531

569

Table 2. Mean total length (TL) and weight (W) of northern snakeheads sampled in the Potomac River system, Virginia, during 2004-2006.

  TL (mm)   ____ W (g)___________ Year N Mean SD Min. Max.   N Mean Min. Max. 2004 20 406 105 88 634 782 553 7 26352005 270 273 120 113 655 493 621 13 31452006 215 475 146 164 765   1381 1009 36 4598

Table 4. Frequency of occurrence (percentage of stomachs containing the taxon) of identifiable taxa consumed by 219 northern snakeheads collected in the Potomac River system, Virginia, during 2004-2006.

Common name   Scientific name Frequency (%)

Banded killifish Fundulus diaphanus 27 White perch Morone americana 5 Pumpkinseed Lepomis gibbosus 5 Bluegill L. macrochirus 5 Goldfish Carassius auratus 2 Gizzard shad Dorosoma petenense 1 American eel Anguilla rostrata 1 Yellow perch Perca flavescens 1 Largemouth Bass Microplevus salmoides 1 Sponail shiner Notropis hudsonius 1 Eastern silvery minnow Hybognathus regius < 1 Mummichog F. heteroclitus < 1 Channel catfish Ictalurus punctatus < 1 Green sunfish L. cyanellus < 1 Tessellated darter Etheostoma olmstedi < 1 Frog Rana spp. < 1 Crayfish Cambaridae < 1

Conclusions:Dramatic increase in catch rates suggests an

overall increase in snakehead population, although an increase in electrofishing capture efficiency could have added some degree of bias.

Maximum size, including total length and weight, increased every year, which suggests that the population matured.

17 species were identified in stomach contents.Female Gonadosomatic Indices rose in early April,

peaked in June, and diminished through September.Counts of daily rings on otoliths of newborns

indicated hatching from mid-June to early September.

Implications:Despite the apparent increase in snakehead

population, the area of colonization did not appear to increase over the original 23-km main stem of the Potomac.

Yearly increase in maximum size is consistent w/ theory that the population was recently established.

Stomach contents consistent w/ theory that snakehead is piscivorous and opportunistic in feeding (ie. Frog, crayfish).

Female GSIs, estimated hatch dates, and the discovery of a nest in early September, indicate a spawning period of at least 5 months in the Potomac.

Works Cited: Virginia Invasive Species Council. 2005. Virginia Invasive Species Management Plan.

Virginia Department of Conservation and Recreation Division of Natural Heritage. Richmond. 84 p.

Invasive Species. 2004. Marek Topoleski, Mary Fabrizio, Ron Lauda. Pg 77-122. Aquatic Community. Northern Snakehead. 2004. Retrieved on Oct. 26, 2009.

<http://www.aquaticcommunity.com/channa/argus.php>. Odenkirk, John, and Steve Owens. Expansion of a Northern Snakehead Population in

the Potomac River System. American Fisheries Society 136:1633-1639, 2007. The Environmental Literacy Council. Snakeehead Fish.. 2008. Retrived on Oct. 25,

2009. < http://www.enviroliteracy.org/article.php/1473.html >.