A population of northern snakeheads Channa argus was documented in the Potomac River system in 2004. The expansion of this population was monitored from 2004 to 2006. Boat electrofishing mean catch per unit effort increased significantly each year from 0.2 fish/h in 2004 to 6.1 fish/h in 2006 (analysis of variance [ANOVA]: P = 0.01). Reported angler catches (N = 24) during 2006 equaled the combined total of the two previous years. Mean total length (TL) and weight (W) in 2006 were 475 mm (SD = 146) and 1,381 g (SD = 1,009), respectively, and maximum size increased each year. The weight‐length relationship for all years combined was logeW = −5.21 + 3.07·logeTL (r2 = 0.996, n = 348). Natural reproduction was confirmed by the location of a nest, and eight year‐classes were estimated based on otolith interpretations. Total annual mortality was estimated to be 38%. Trends in female gonadosomatic index and otolith daily ring counts of age‐0 fish suggested protracted or repeat spawning from May to September. Females were fecund, carrying an average of 40,786 eggs. Collection patterns suggested that this population of northern snakeheads originated from Dogue Creek. Seventeen food items, including 15 fish species, were identified from stomach contents. The banded killifish Fundulus diaphanus was the dominant food item. Bluegills Lepomis macrochirus, pumpkinseeds L. gibbosus, and white perch Morone americana were also commonly consumed. Although population size increased, known range did not appear to increase or increased at a slower rate. Increases in angler catch during 2006 at the northern and southern termini of the existing distribution suggest that northern snakehead range expansion is imminent.

A population of northern snakeheads Channa argus was documented within a 23‐km reach of the main‐stem tidal freshwater Potomac River and associated tributaries in 2004. Twenty northern snakeheads were collected with a variety of gears, including hook and line and electrofishing. The dominant habitats were shallow waters with floating or emergent vegetation. Natural reproduction had probably occurred, based on identification of five year‐classes and the collection of an age‐0 fish. The length frequency and age distributions suggested an established population. Many of the fish collected were gravid females. Adult total length (TL) and weight (W) ranges were 305–634 mm (mean = 423 mm; SD = 76 mm) and 348–2,635 g (mean = 831 g; SD = 532 g). The length–weight relationship was logeW = −4.85 + 2.93·logeTL (r2 = 0.99; n = 20). The collection pattern suggested that the northern snakeheads in the Potomac River originated from Dogue Creek, as 50% of those collected came from this watershed.

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A Northern Snakehead Channa argus population was documented in the Potomac River system in 2004. Since that time, the population has expanded in range and number, yet relatively little is known about key population variables including age and growth. Lack of known‐age fish with which to compare otoliths from the sampled population has hindered verification, and Northern Snakehead otoliths can be difficult to interpret. We compared growth increments (mm/d) of recaptured fish marked with T‐bar anchor tags (n = 51; mean time at large, 310 d [SD = 302]) to otolith annuli from fish sacrificed in 2011 and 2012 (n = 192). While immersed (solution of 80% water and 20% glycerin) otolith transverse perspectives were viewed “cracked” with transmitted light. Readings from fish aged 1–4 years suggested initial growth was much faster than previously reported, but length at age was highly variable. Annual growth increments for fish aged 1–4 (mean length at age of fish, respectively: 394, 563, 644, and 721 mm TL) were converted to estimated daily growth (mm/d), which was reasonably similar to the daily growth of recaptured tagged fish. Von Bertalanffy growth parameters were L∞ = 780, K = 0.48, and t 0 = −0.56, where L∞ is the asymptotic length, K is a growth coefficient, and t 0 is a time coefficient at which length would theoretically be zero. The implications of rapid growth include the potential for the earlier onset of sexual maturity, which could represent enhanced chances for successful colonization.Received November 20, 2012; accepted May 15, 2013