2010 NORTHEASTERN NATURALIST 17(2):325–332
First Record of a Northern Snakehead
(Channa argus Cantor) Nest in North America
Andrew M. Gascho Landis1,2 and Nicolas W.R. Lapointe1,*
Abstract - A population of Channa argus (Northern Snakehead) has been established
in the Potomac River catchment, VA and MD, for approximately ten years,
and is increasing rapidly in abundance. Little is known about life-history strategies
of this species in North American environments. We report the first discovery of a
Northern Snakehead nest in North America and discuss some of its nesting habits.
Adult Northern Snakeheads constructed a circular nest in a patch of dense Hydrilla
verticillata (Hydrilla) by clipping stems, thus creating a canopy of floating plants.
They laid eggs atop floating stems, and larvae hatched within three days. Both male
and female parents were observed guarding the eggs and fry in the nest. Parents also
continuously guarded the school of fry as they dispersed from the nest. Prolonged
schooling behavior after leaving the nest accompanied parental guarding for up to
several weeks. Floating nests and parental care likely increase reproductive success
in a tidally influenced ecosystem with abundant predators. These factors contribute to
the ability of Northern Snakehead to persist and spread in North America. Based on
our findings, nests will likely be located in areas of the Potomac River that are low
to no flow, moderately shallow, and highly vegetated.
Introduction
Channa argus Cantor (Northern Snakehead) (formerly Ophiocephaluarus
argus warpachowskii) is a newly introduced species in the United
States. This species is thought to have been introduced as a product from
live-fish markets (Courtenay and Williams 2004). The first US specimen
was captured in the Potomac River, Fairfax County, VA, in May, 2004
(Orrell and Weigh 2005). By 2005, this species was considered established
(Odenkirk and Owens 2005). Using otoliths to age fish captured
in 2004, specimens were determined to be up to 6 years old, suggesting
an introduction date as early as 1998 (Odenkirk and Owens 2005).
Through continued monitoring of Northern Snakehead, Odenkirk and
Owens (2007) documented growth in population size and range expansion
within the Potomac River catchment. Little is known about what
drives the success of this species in the Potomac River and what factors
could potentially limit its spread.
The reproductive process may represent a vulnerable link in Northern
Snakehead’s life cycle, and a more complete understanding of it can enhance
1Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and
State University, 100 Cheatham Hall, Blacksburg, VA 24061. 2Current address -
Department of Fisheries and Allied Aquaculture, Auburn University, 203 Swingle
Hall, Auburn, AL 36849. *Corresponding author - nlapointe@gmail.com.
326 Northeastern Naturalist Vol. 17, No. 2
our ability to manage this species (Jiao et al. 2009). Researchers have described
nesting habits for Northern Snakehead in its native range in China
(Ling 1977) and introduced range in Kazakhstan (Dukravets and Machulin
1978). Adult fish clear a circular area in shallow aquatic vegetation for a nest
(Amanov 1974). Northern Snakehead eggs are positively buoyant and float
at the water surface. In China, the adult fish have been observed guarding the
eggs and young (Courtenay and Williams 2004). Since Northern Snakehead
are a popular food fish and perform well in ponds, observations in its native
range occurred at aquaculture facilities, and habits in this artificial environment
may have little bearing for the strategies employed by wild Northern
Snakeheads in the Potomac River.
Resource managers and researchers have spent many hours on the
Potomac River in an effort to monitor and research Northern Snakeheads
(J. Odenkirk, Virginia Department of Game and Inland Fisheries, Fredericksburg,
VA, pers. comm.). While in the field, researchers actively
searched for nests and nesting habitat in an effort to understand more about
the species’ life history (Lapointe and Angermeier 2009). However, even
with information from the literature as to how this species behaved in its
native range, Northern Snakehead nests were not identified in the first three
years after their populations had been recognized as established (Odenkirk
and Owens 2007). In this paper, we document the first observations of a
nest and nesting habits for Northern Snakehead in the Potomac River. We
compare our observations of Northern Snakehead nesting strategies in this
novel ecosystem with nesting strategies documented in its native range.
Methods
The study location for our observations was the Potomac River and its
tributaries south of Washington DC. Daily tides influence this stretch of
river, causing changes in water depth of up to 1.5 m (USGS gauging station,
Alexandria, VA); however, this portion of river does not experience
significant levels of salinity (typically 0.1–0.2 ppt). This area features bays
at the terminus of each tributary. Bays are often shallow (<2 m), highly vegetated,
and, with the exception of tidal fluctuations, have very little current.
Aquatic vegetation comprises both emergent plants (Nuphar varigateum
Durand [Yellow Pond-lily], Phragmites australis (Cav.) Trin. ex Steud.
[Common Reed], Typha latifolia L. [Broadleaf Cattail]) and submerged
plants (Hydrilla verticillata (L.F.) Royle [Hydrilla], Myriophyllum spicatum
L. [Eurasian Watermilfoil], Ceratophyllum demersum L. [Coon's Tail], and
Najas sp.water nymph]).
A radio-telemetry study (Lapointe and Angermeier 2009), which took
place between October 2006 and October 2007, allowed us to find exact
locations of Northern Snakeheads and make repeated visits. The telemetry
study included 49 fish, from several locations throughout the Potomac
2010 A.M. Gascho Landis and N.W.R. Lapointe 327
River, which received a surgically implanted radio transponder. On two
separate occasions, brooding fish were located during routine telemetry
surveys: the first of these two was guarding a nest of eggs, and the second
was guarding a school of young. Both brooding fish were found in August
2007. By tracking the first guarding adult, we were able to follow the
school of larval fish after the nest was abandoned. At the nest site, we were
able to make observations without disturbing nesting activities due to its
location in close proximity (approximately 1 m) to a residential flood wall,
built to buffer against high water. We recorded most observations while
hidden on the flood wall. No nest was located for the second guarding
snakehead, and the young were discovered after the eggs had hatched and
the young had left the nest.
We took additional measurements from a boat to record the size and
shape of the Northern Snakehead nest without disturbing its structure. Habitat
measurements such as water depth, substrate and aquatic vegetation
type, temperature, and dissolved oxygen were recorded to help characterize
nesting location and sites used by the school of young. We recorded GPS
location to track distance movement of the larval Northern Snakeheads
after they dispersed from the nest. At each visit, our goal was to collect
approximately 30 larval fish by dip net; however, the range of captures
was between 8 and 50 fish. This level of collection allowed us to obtain
a representative sample size, yet keep our impact on the school of larvae
minimal. Additionally, we captured several Gambusia holbrooki Girard
(Eastern Mosquitofish) observed feeding on Northern Snakehead fry. All
fishes were preserved in 10% formalin and returned to the laboratory. The
total lengths of Northern Snakehead larvae were measured and presented
as means with standard deviation. Eastern Mosquitofish stomach contents
were examined.
Results
The breeding pair of Northern Snakeheads guarding a nest was found in
Little Hunting Creek, a tributary of the Potomac River. The nest was located
in a small, side-channel creek, dredged to allow access to personal docks and
a boat launch, even at times of low water. Hydrilla dominated the shallow
shoreline, while the central channel was free of vegetation. Adult Northern
Snakeheads had clipped Hydrilla stems, which then floated at the water
surface. Unclipped, living Hydrilla surrounded the clipped Hydrilla stems.
A mass of eggs floated at the water’s surface above the radio-tagged fish in
the matrix of clipped Hydrilla. Bright orange-yellow eggs were held in place
by the floating Hydrilla leaves and stems. Although floating freely, the eggs
had formed into rows resembling a honeycomb, which were one to three layers
deep and 25 cm in diameter. Below the canopy of floating Hydrilla, an
open area was created in which parents could patrol (Fig. 1). The nest was
328 Northeastern Naturalist Vol. 17, No. 2
approximately circular in shape, with a diameter of 1.8 m, and depending
on tidal variation, had a depth between 25 and 125 cm. Several openings
(10–20 cm in diameter) in the floating Hydrilla mat were located around the
perimeter of the nest. These were used by adults for obligate air-breathing.
Substrate at the nest site was sand. Dissolved oxygen and temperature on
the day we found the nest were 7.8 mg/L and 29.4 °C, respectively. Pictures
of the nest, eggs, and young, along with descriptions, are available at
www.fishwild.vt.edu/snakeheads.
Both the male and female Northern Snakeheads guarded eggs and fry
throughout incubation and development. Guarding behavior was exemplified by active swimming underneath the eggs and fry. Swimming typically
occurred in a circular pattern with occasional breaks for aerial respiration.
These activities probably protected the eggs and young from aquatic predators.
Previous field observations and dissection for diet analysis noted sexual
dimorphism for Northern Snakehead (N.W.R. Lapointe, unpubl. data). Male
fish have a darker coloration and a broader head than female fish. Both
morphs of fish were present; thus, we concluded that the two fish guarding
the nest were male and female parents.
On the third consecutive day of our observations, Northern Snakehead
eggs had begun to hatch. Fry moved from the original hatching site, but
stayed within the larger nest area on the third day after hatching. By the
fourth day after hatching, fry averaged 6.3 mm ± 0.5 SD (n = 29 individuals)
total length and had moved 5 m from the nest site. Movement
of the school progressed in a downstream direction, and fry remained in
the cover of Hydrilla. On the eleventh and final day of observation, fry
averaged 12 mm ± 0.5 SD (n = 30) in length and were located an average
Figure 1. Artistic rendition of a male and female Northern Snakehead guarding eggs
in a circular nest of Hydrilla.. Black dots represent eggs floating in a matrix of floating
fronds of clipped Hydrilla.
2010 A.M. Gascho Landis and N.W.R. Lapointe 329
of 80 m ± 9 SD from the nest site. Daily distances moved by the school
were sporadic, but averaged about 10–15 m per day. The movement of the
school was accompanied by the tagged parent. Parents were not always
observed guarding the school, but the school was located via telemetry. It
is unclear whether the untagged parent continued to guard the school after
it moved beyond the nest.
While observing the nest immediately after start of hatching, we noted
that individual Eastern Mosquitofish began invading the nest site and observed
them consuming Northern Snakehead eggs and fry. To document
predation of egg and fry, we captured four Eastern Mosquitofish for laboratory
diet analysis. All four specimens contained eggs and newly hatched
Northern Snakehead fry; the largest Eastern Mosquitofish (43 mm) contained
60 snakehead eggs and fry, and the smallest (31 mm) contained 21 snakehead
eggs and fry. There appeared to be a correlative relationship between the size
of predator and the number of fry consumed.
Concurrent to our nest observation, the second radio-tagged Northern
Snakehead we followed was guarding young that were 14.3 mm ± 0.9 SD
(n = 30) in length. These fish, located in Douge Creek Bay, also utilized
dense Hydrilla mats. We followed this school of young fish for 13 days
after its discovery. Mean fish size at the end of the observation period was
39.9 mm ± 2.0 SD (n = 8) total length.
Discussion
Our efforts identified the first recorded Northern Snakehead nest in
North America. Despite intensive searching, Northern Snakehead nests
have proven difficult to locate. In the concurrent radio telemetry study
(Lapointe and Angermeier 2009), 49 fish were tracked twice a week from
April through August, which corresponds to the predicted breeding season.
This extensive time in the field yielded only two brooding fish. Although
the primary focus of the radio telemetry study was not locating Northern
Snakehead nests, tracking repeatedly brought us in close proximity (≈1 m)
of many Northern Snakeheads, and our sampling included quantifying vegetative
habitat, ensuring an examination of potential nesting sites. The size
and shape of the nest discovered in the Potomac River catchment matched
the description of nests from Northern Snakeheads in their native range
(Courtenay and Williams 2004); however, there are important distinctions.
Courtenay and Williams (2004) reported nests of Northern Snakehead from
China that are 1 m in diameter, in approximately 0.6–0.8 m of water that
had been cleared of vegetation. Also, in China, Ling (1977) documented
that a congener of Northern Snakehead, Channa striata Bloch (Chevron
Snakehead), bit off aquatic vegetation to clear an area for a spawning nest,
and its floating eggs were contained by the vegetation. The descriptions
from the Asian literature portray a nest as an area cleared of vegetation
330 Northeastern Naturalist Vol. 17, No. 2
with the parent fish visibly occupying the interior. From our observations
in the Potomac River, Northern Snakehead nests are quite difficult to
discover because floating vegetation camouflages the nest and eggs, and
masks the parents’ presence.
Our observations in the Potomac River expand on the literature and can
help us identify factors related to nesting habitat requirements and behaviors
that make Northern Snakeheads successful invaders. Nesting habitat requirements
include low current velocity and low wave action plus dense beds of
submerged aquatic vegetation; additionally, long-term parental brooding
contributes to their invasiveness.
Although the two areas in which we located guarding adults were fundamentally
different (one was an open bay, the other a coastal plain stream),
they shared some habitat features. The sites had little to no flow and were
largely protected from wave action. These features are necessary because
Northern Snakeheads produce a floating cluster of eggs that could potentially
break apart and float away.
All observations of young Northern Snakeheads occurred in dense beds
of submerged aquatic vegetation. Floating, clipped macrophytes provided
ideal cover for guarding parents from avian or terrestrial predators, while
simultaneously providing an open area immediately below the nest where
parents could patrol and guard eggs or young. Most importantly, floating
macrophytes surrounded the floating egg mass, keeping it in place. Interestingly,
all schools of juvenile Northern Snakeheads that we observed in the
Potomac River catchment in 2007 were associated with dense patches of
Hydrilla. While Hydrilla is an introduced species in the Potomac River, it
provides a greater abundance of aquatic macroinvertebrates than do open
water areas (Thorp et al. 1997). In lakes in Florida, Hydrilla harbored
higher macroinvertebrate abundance than the neighboring native vegetation
(Schramm et al. 1987). Success of young Northern Snakeheads might
be linked to abundance of Hydrilla in the waterways of the Potomac River
because it provides cover and abundant food resources. More research is
necessary to establish the connection between these two exotic organisms.
Our observations showed that adult Northern Snakeheads guard their
young after they leave the nest and stay with them for at least four weeks.
Ling (1977) was able to observe that male fish closely guarded their young
for six to nine weeks, which coincided with juvenile dispersal. Continued
guarding is possible due to the schooling behavior of snakehead fry when
they leave the nest. Extended parental guarding has potential to increase
larval and juvenile survival, helping Northern Snakeheads to be successful
in the Potomac River (Odenkirk and Owens 2007).
Separate from our observations of the factors leading to the success of
Northern Snakeheads, we documented Eastern Mosquitofish consuming
snakehead eggs. Eastern Mosquitofish routinely prey on eggs and larvae
of many species (Mills et al. 2004) and significantly reduce invertebrate,
2010 A.M. Gascho Landis and N.W.R. Lapointe 331
amphibian, and fish populations in a wide range of ecosystems (Courtenay
and Meffe 1989). We documented substantial egg predation by only a few
individuals of Eastern Mosquitofish in a short period of time. The true impact
of this egg predator is unknown, but it could have the potential to impact
Northern Snakehead recruitment.
We hope this information will give resource managers and researchers
a better search image for Northern Snakehead nests in the future. Through
understanding nest placement, structure, and habitats, future studies can be
conducted to improve our knowledge of this novel predator. Based on our
findings, nests will likely be located in areas of the Potomac River that are
low to no flow, moderately shallow, and highly vegetated.
Acknowledgments
The authors thank Debbie Lapointe for the artwork in Figure 1. This research was
funded by a grant from the USGS Invasive Species Program and by a Natural Science
and Engineering Research Council of Canada post-graduate fellowship. The Virginia
Department of Game and Inland Fisheries contributed time and equipment, and Fort
Belvoir provided boat storage and launching facilities.
Literature Cited
Amanov, A.A. 1974. Morphology and mode of life in the Amur Snakehead
(Ophiocphalus argus warpachowskii) in Chimkurgan reservoir. Journal of Ichthyology
14:713–717.
Courteney, W.R., and G. Meffe. 1989. Small fishes in strange places: A review of
introduced poecillids. Pp. 319–331, In G. Meffe and F. Snelson, Jr. (Eds.). Ecology
and Evolution of Livebearing Fishes (Poeciliidae). Prentice Hall, Engelwood
Cliffs, NJ.
Courtenay, W.R., and J.D. Williams. 2004. Snakeheads (Pisces, Channidae)—A
biological synopsis and risk assessment. US Department of the Interior, US Geological
Survey Circular 2004:1–143.
Dukravets, G.M., and A.I. Machulin. 1978. The morphology and ecology of the
Amur Snakehead, Ophiocephalus argus warpachowskii, acclimatized in the Syr
Dar'ya Basin. Journal of Ichthyology 16:203–208.
Jiao, Y., N.W.R. Lapointe, P.A. Angermeier, and B.R. Murphy. 2009. Hierarchical
demographic approaches for assessing invasion dynamics of a non-indigenous
species: An example using Northern Snakehead (Channa argus). Ecological
Modeling 220:1681–1689.
Lapointe, N.W.R., and P.L. Angermeier. 2009. Movement, habitat use, nesting, and
feeding of Northern Snakehead (Channa argus) in the Potomac River catchment.
Project report to the United States Geological Survey, Reston, VA. 7 pp.
Ling, S.W. 1977. Aquaculture in southeast Asia: A historical overview. University of
Washington Press, Seattle, WA.
Mills, M.D., R.B. Rader, and M.C. Belk. 2004. Complex interactions between native
and invasive fish: The simultaneous effects of multiple negative interactions.
Oecologia 141:713–721.
Odenkirk, J., and S. Owens. 2005. Northern Snakeheads in the tidal Potomac River
system. Transactions of the American Fisheries Society 134:1605–1609.
332 Northeastern Naturalist Vol. 17, No. 2
Odenkirk, J., and S. Owens. 2007. Expansion of a Northern Snakehead population
in the Potomac River system. Transactions of the American Fisheries Society
136:1633–1639.
Orrell, T.M., and L. Weigh. 2005. The Northern Snakehead Channa argus-
(Anabantomorpha:Channidae), a non-indigenous fish species in the Potomac
River, USA. Proceedings of the Biological Society of Washington 118:407–415.
Schramm, H.L., K.J. Jirka, and M.V. Hoyer. 1987. Epiphytic macroinvertebrates on
dominant macrophytes in two central Florida lakes. Journal of Freshwater Ecology
4:151–161.
Thorp, P.G., R.C. Jones, and D.P. Kelso. 1997. A comparison of water column macroinvertebrate
communities in beds of differing submersed aquatic vegetation in
the tidal freshwater Potomac River. Estuaries 20:86–95.