Montana Field Guide

The Northern Snakehead (NOSN) is a long, slender fish with a single dorsal fin running the length of the fish (Fuller et al. 2018 ). Maximum size exceeds 85 cm (33 inches)(Fuller et al. 2018 ). The Overall color of this species is brown with dark blotches (Fuller et al. 2018 ). It has a somewhat flattened head with eyes that are located in a dorsolateral position on the anterior part of the head; anterior nostrils are present and tubular; dorsal and anal fins are elongated, and all fins are supported only by rays (Courtenay and Williams 2004). Males are darker in color, and have a broader head, as compared to females (Gascho Landis and Lapointe 2010). Juveniles have a similar color and pattern as the adults. NOSN are morphologically similar to the North American native Bowfin (Amia calva), and the two are often misidentified (Fuller et al. 2018 ). Snakeheads can be distinguished from Bowfin by the position of pelvic fins (directly behind pectoral fins in snakeheads, farther back on body in Bowfin. It could also be mistaken for the MT native fish, the burbot (Lota lota).

Snakeheads can be distinguished from Bowfin by the position of pelvic fins (directly behind pectoral fins in snakeheads, farther back on body in Bowfin) and the size of the anal fin (elongate and similar in size to dorsal fin in snakeheads, short and much smaller than dorsal fin in Bowfin) (Fuller et al. 2018 ). Additionally, Bowfin can be identified by the presence of a bony plate between the lower jaws (gular plate) and a distinctive method of swimming through undulation of the dorsal fin (Fuller et al. 2018 ). NOSN is also very similar to the Burbot (Lota lota), another North American native fish species (Fuller et al. 2018 ), but does not have a single barbel on its chin.

Although Northern snakeheads can survive up to four days out of the water, overland migration is only possible for juveniles (Courtenay and Williams 2004). The rounded body of the adult northern snakehead is not as conducive to overland migration as observed in more horizontally flattened snakehead species (Fuller et al. 2018 ).

This species prefers to live in stagnant, shallow (<2 m) ponds or swamps with mud substrate or aquatic vegetation and slow muddy streams, it also occurs in canals, reservoirs, lakes, and rivers (Courtenay and Williams 2004).

Adult snakeheads feed almost exclusively on other fishes (>97% of diet), with the remainder of their diet composed of crustaceans, frogs, small reptiles, and sometimes small birds and mammals (Courtenay and Williams 2004; Saylor et al 2012). Northern snakehead fry initially feed on zooplankton, before moving on to a diet of small insects and crustaceans (e.g., cladocerans, copepods, small chironimid larvae) (Fuller et al. 2018 ). Juveniles may feed on small fish, including goldfish (Carassius spp.) and roach (Rutilis spp.; Courtenay and Williams 2004). As an adult, the NOSN is a voracious feeder (Okada 1960), and its diet may include fish up to 33 percent of its body length (Courtenay and Williams 2004). Adult prey items have included: loach, sunfish, carp, perch, zander, grass carp, catfishes, crayfish, dragonfly larvae, beetles, and frogs (Fuller et al. 2018 ). These predatory fishes may compete with native species for food and habitat (Fuller et al. 2018 ). Juveniles eat zooplankton, insect larvae, small crustaceans, and the fry of other fish (Fuller et al. 2018 ).

Northern snakeheads are obligate air-breathers, capable of survival in poorly oxygenated waters (Fuller et al. 2018 ). Although this species prefers to live in stagnant shallow (< 2 m) ponds or swamps with mud substrate or aquatic vegetation and slow muddy streams, it also occurs in canals, reservoirs, lakes, and rivers (Courtenay and Williams 2004). This species does show some seasonal changes microhabitat selection and preference, utilizing deeper water in winter months and shallow areas with macrophytes during the spawning season (Lapointe et al. 2010). It can adapt to a wide range of aquatic environments, as evidenced by the spread of reproducing, introduced populations throughout Asia and Japan (Fuller et al. 2018 ). While its optimum maximum air temperature range is 5-16°C (Herborg et al. 2007), the northern snakehead has a wider latitudinal range and temperature tolerance (0 to >30°C, including frost days) than other snakehead species (Dukravets and Machulin 1978, in Courtenay and Williams 2004; Okada 1960). Reduced metabolism and oxygen demand at low temperatures allows this species to survive extended periods of ice cover (Frank 1970, in Courtenay and Williams 2004). Upper salinity tolerances have been experimentally determined to be between 15 and 18 ppt (at temperatures of 15-24°C; NSWG 2006).

In its native range, NOSN reproductive maturity is typically reached when fish are 2-3 years old (Dukravets and Machulin 1978), but may occur only after one year of growth in some introduced populations (USACE 2011). In the U.S., NOSN spawning has been observed to start by the end of April, peak in June, and continue through August (Gascho Landis et al. 2011). Adult females build circular floating nests from clipped aquatic plants and release their pelagic, nonadhesive, buoyant eggs on top (Gascho Landis and Lapointe 2010). Each spawn can consist of 1300-1500 bright orange-yellow eggs (about 1.8 mm diameter), with up to five spawns occurring within a year. NOSN fecundity can range from 22,000-51,000 in its native range (Amur River basin; Nikol'skiy 1956) to 28,600-115,000 in an introduced population (Syr Dar'ya basin, Turkmenistan/Uzbekistan; Dukravets and Machulin 1978). Both parents guard the nest of eggs from predation and continue to guard the hatched fry for several additional weeks (Courtenay and Williams 2004, Gascho Landis and Lapointe 2010). Depending on water temperature, eggs may hatch in fewer than three days (28 hours at 31°C, 45 hours at 25°C, and 120 hours at 18°C; Gascho Landis and Lapointe 2010). Larvae experience rapid growth after their first two weeks, though overall individual growth rate in North American populations appears to be less than that in both native and introduced Asian populations (Gascho Landis et al. 2011).

While its optimum maximum air temperature range is 5-16°C (Herborg et al. 2007), the northern snakehead has a wider latitudinal range and temperature tolerance (0 to > 30°C, including frost days) than other snakehead species. Reduced metabolism and oxygen demand at low temperatures allows this species to survive extended periods of ice cover. The NOSN has become widely popular in ethnic markets and restaurants over the last two decades, such that this species comprised the greatest volume and weight of all live snakehead species imported into the U.S. until 2001 (Courtenay and Williams 2004, NSWG 2006). Snakehead's resilient nature reportedly makes them more desirable than carps for ceremonial release, and some interest in recreational fishing may also exist (Mendoza-Alfaro et al. 2009, NSWG 2006).

Due to this species' temperature tolerance range, it would likely survive in a host of waterbodies in Montana if introduced to the state; therefore, keeping this species out of the state is the best preventative measure from it becoming another invasive species in the state.