Invasion History

First Non-native North American Tidal Record: 1874
First Non-native West Coast Tidal Record: 1874
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Brown Bullheads (Ameiurus nebulosus) are native through the interior basins from southwest Saskatchewan to the St. Lawrence estuary in Quebec, and Arkansas to Florida. On the Atlantic coast, this catfish ranges from the tip of Florida to New Brunswick (Page and Burr 1991; USGS Nonindigenous Aquatic Species Program 2014). They have been widely introduced in western North America. They were first stocked in the Sacramento River in 1874 (Cohen and Carlton 1995; Dill and Cordone 1997), then to the Columbia River in 1894 (Lampman 1946), and the Fraser River, British Columbia (Carl and Clemens 1967). In British Columbia, the first releases occurred on Vancouver Island and the lower Fraser River (Carl and Giguet 1967; Richardson et al. 2000). They have also been introduced in Puerto Rico, much of Europe, and New Zealand (Lever 1996)

North American Invasion History:

Invasion History on the West Coast:

In 1874, Livingston Stone, of the California Fish Commission planted 74 'Horned Pout' from Vermont in ponds and sloughs near Sacramento (Smith 1895). The early history of the population is difficult to determine, since Smith lumps all 'catfishes' together. However, the Brown Bullhead became the most widely distributed catfish in California (Dill and Cordone 1997; Moyle 2002). In the San Francisco Bay estuary only 0.3% percent of the catfish collected in Delta surveys in the 1960s were Brown Bullheads (Turner 1966, cited by Cohen and Carlton 1995). In recent surveys in the fresh waters of the Delta, they have had a similar rank, well below White Catfish (Feyrer and Healy 2003; Brown and Michniuk 2007; Sommer et al. 2014). In one survey of tidal fresh marshes, in shallower waters, Brown Bullheads outnumbered White Catfish, but both were relatively rare (Grimaldo et al. 2012). Brown Bullheads also occurred in the fresh-brackish Suisun Marsh, but were much less abundant then White Catfish (Matern et al. 2002).

In 1882, 'catfish' were stocked in Silver Lake, Washington, on the Cowlitz River, which joins the Columbia River downstream of Portland. By 1890, catfish, presumably Brown Bullheads, were swarming on Sauvie Island, in the Columbia River. A collection of catfish from the Willamette and Columbia in 1945 was dominated by Brown Bullheads (Lampman 1945). In more recent surveys in the Portland area, both Brown and Yellow Bullheads were present, but in relatively small numbers, compared to other species (Hughes and Gammon 1987; Farr and Ward 1994; Van Dyke et al. 2009).

Brown Bullheads were introduced to lakes on Vancouver Island, possibly by a restaurant owner who kept them in a display tank. By 1953, the fish had been introduced to multiple lakes on the island and were established in the lower tidal Fraser River (Carl and Giguet 1967; Carl and Giguet 1972).

Invasion History in Hawaii:

Brown Bullheads were stocked in freshwaters in Oahu in 1893 but did not become established (Maciolek 1984).

Invasion History Elsewhere in the World:

Brown Bullheads have been introduced to Puerto Rico, 21 European countries, Iran, Turkey, Vietnam, China, and New Zealand. Some of these invasions have failed or resulted in uncertain establishment (Froese and Pauly 2018). Another source of uncertainty is the frequent confusion of Black and Brown Bullheads (Copp et al. 2015). Brown Bullheads were first introduced to reservoirs in southwestern Puerto Rico in 1915 and are established in many reservoirs (Lever 1996, USGS Nonindigenous Aquatic Species Program 2018). Between 1871 and 1950, both Black and Brown Bullheads were introduced to 21 different European countries, and transferred between countries. Most of the introductions were assumed to be Brown Bullheads, but many were later identified as Black Bullheads (Lever 1996; Copp et al. 2016; Froese and Pauly 2016). In 1877, 140 or 225 Brown Bullheads misidentified as 'Pimelodus cattus' were stocked in lake in Auckland, New Zealand, and rapidly reproduced, and is now established in many lakes and rivers on the North and South Islands, where it is often caught by eel fishers (Lever 1996).


Brown Bullheads (Ameiurus nebulosus) are freshwater catfish. Bullhead Catfishes (Ictaluridae) have four pairs of barbels, no scales, an adipose fin, stout spines at the origins of the dorsal and pectoral fins, and abdominal pelvic fins. The caudal fin of the Brown Bullhead is rounded or nearly straight. The base of the anal fin is relatively short, and rounded with 20-24 rays, with the anterior rays shorter than the posterior ones. The dorsal fin has one spine and six rays. The rear edge of the pectoral spines has 5-8 saw-like teeth. Adults can reach 500 mm but are usually below 300 mm. Brown Bullheads are olive to brown above, with dark brown of black mottling, yellow-olive on the sides, and white to yellow below, with dusky to black fins. The chin barbels are dark (Page and Burr 1991; Jenkins and Burkhead 1993; Murdy et al. 1997; Moyle 2002).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Vertebrata
Superclass:   Osteichthyes
Class:   Actinopterygii
Subclass:   Neopterygii
Infraclass:   Teleostei
Superorder:   Ostariophysi
Order:   Siluriformes
Family:   Ictaluridae
Genus:   Ameiurus
Species:   nebulosus


Ictalurus nebulosus (, None)
Pimelodus nebulosus (Leseur, 1819)
Silurus coenosus (Richardson, 1836)
Pimelodus atrarius Pimelodus atrarius (DeKay, 1842)
Pimelodus vulgaris (Thompson, 1842)
Pimelodus marmoratus (Holbrook, 1855)

Potentially Misidentified Species

Ameiurus natalis
Ameiurus natalis (Yellow Bullhead) is native to the Atlantic Slope and Mississippi-Great Lakes basin, and has been introduced to the San Francisco estuary and the Columbia River. The tail is squared-off, the pectoral spine has sawlike teeth, and the chin barbels are white or yellow (Page and Burr 1991).

Ameiurus nebulosu
Ameiurus nebulosus (Brown Bullhead) is native to the Atlantic Slope and Mississippi-Great Lakes basin, and has been introduced to the San Francisco estuary and the Columbia River and Fraser Rivers. The tail is squared-off, the pectoral spine has saw-like teeth, and the chin barbels are dark. The body has dark brown mottling (Page and Burr 1991).

Amieurus catus
Ameiurus catus (White Catfish) is native to the Atlantic Slope and has been introduced to the San Francisco estuary and the Columbia River. The tail is forked, the pectoral spine has saw-like teeth, and the chin barbels are white (Page and Burr 1991).

Amieurus melas
Ameiurus melas (Black Bullhead) is native to the Mississippi-Great Lakes basin, and has been introduced to the San Francisco estuary and the Columbia River. The tail is squared-off, the pectoral spine lacks sawlike teeth, and the chin barbels are dark (Page and Burr 1991).

Ictalurus furcatus
Ictalurus furcatus (Blue Catfish) are native to the Mississippi-Gulf Basin, and has been introduced, but is rare, in the San Francisco estuary. Adults are very large (to 1650 mm), and bluish gray in color, without dark mottling. The caudal fin is deeply forked and the anal fin has a straight edge but is tapered posteriorly (Page and Burr 1991).

Ictalurus punctatus
Ictalurus punctatus (Channel Catfish) are native to the Mississippi-Gulf Basin, and the southeastern Coastal Plain, and have been introduced to the San Francisco estuary and the Columbia River. Adults are large (to 1350mm) and gray in color, with scattered dark spots. The caudal fin is deeply forked and the anal fin has a curved edge (Page and Burr 1991).



Brown Bullheads (Ameiurus nebulosus) are freshwater catfish. Male and females do not have obvious morphological differences. Given their range of habitats, Brown Bullheads probably vary greatly in growth and life history according to environment and crowding. Adults mature in 2-3 years, at ~178 mm. Males tend to be larger than females. Spawning occurs at 14-29 C (Jones et al. 1978; Jenkins and Burkhead 1993). Brown Bullheads can spawn in an open excavated nest, or in the shelter of natural objects, such as logs, rocks, and vegetation, or in artificial objects, such as flowerpots, tires, tin cans, or cement blocks (Wang 1986; (Jones et al. 1978; Jenkins and Burkhead 1993). Females contain 2,000-13,000 eggs (Jones et al. 1978). During spawning, the male and female often embrace in a head-to-tail fashion, with the males' tail curled around the female's head. The eggs are guarded by the male, or the female, but or by both parents. Prolarvae remain in the nest until the yolk-sac is absorbed. When the yolk-sac is absorbed, fin-ray development is complete, and the fish are juveniles, Like other bullheads, the juveniles swim in dense schools in shallow water. Brown Bullheads can live for 7 to 10 years (Jones et al. 1978; Wang 1986; Jenkins and Burkhead 1993).

Brown Bullheads range from cold-temperate to subtropical climates and tolerates temperatures from near 0 C in ice-covered rivers in winter, to 37.5 C (Jones et al. 1978). Adults tolerate salinities up to 10 PSU in the field (Jones et al. 1978). Their habitats include 'pools, and sluggish runs over soft substrates in creeks and small to large rivers, impoundments, oxbows, and ponds (Page and Burr 1991). They occur 'mostly in the shallow vegetated areas in the sloughs of the Delta; shallow water of reservoirs, such as Millerton Lake, Folsom Lake; small ponds, such as Heather Farm Pond of Walnut Creek; stagnant weedy creeks, such as the Napa River (this study)'; (Turner 1966a, cited by Wang 1986). Brown Bullheads are omnivorous and eat aquatic plants, benthic invertebrates, and small fishes (Jenkins and Burkhead 1993). In the Delta, these fish were feeding predominantly on amphipods, isopods, crayfish, dragonfly larvae, and snails (Moyle 2002). Predators include larger fish, birds, and humans.


General HabitatNontidal FreshwaterNone
General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatSwampNone
General HabitatTidal Fresh MarshNone
General HabitatUnstructured BottomNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Vertical HabitatNektonicNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)0Based on geographical range
Maximum Temperature (ºC)37.5Experimental (Jones et al. 1978)
Minimum Salinity (‰)0Freshwater species
Maximum Salinity (‰)10Field (Jenkins and Burkhead 1993)
Minimum Dissolved Oxygen (mg/l)0.2Field (Jones et al. 1978)
Minimum Reproductive Temperature14Field (Jenkins and Burkhead 1993)
Maximum Reproductive Temperature29Field (Jenkins and Burkhead 1993)
Minimum Reproductive Salinity0This is a freshwater fish.
Minimum Length (mm)178Minimum length at maturity (Jones et al.1978).
Maximum Length (mm)465Page and Burr 1991, but more usually below 300 mm (Jenkins and Burkhead 1994).

General Impacts

Brown Bullheads (Ameiurus nebulosus) have been introduced around the world as a food and sport fish. Fish from clean water can provide pleasant sport, and have good flavor, but once established in muddy or polluted water, they are often under-appreciated (Moyle 2002). Brown Bullheads are a potential predator on and competitor with many small native fishes (Nowosad and Taylor 2012; Dextrase and Mandrak 2012).

Economic Impacts

Fisheries- Brown Bullheads were widely introduced in inland waters in the Western states, and are a popular sportfish, but they are regarded as a pan-fish, and are not targeted as major game-fish (Moyle 2002). In San Francisco Bay, they are less abundant than the White Catfish (Ameiurus catus) or the Channel Cafish (Ictalurus punctatus), which are larger and preferred by the sport fishery (Dill and Cordone 1997; Moyle 2002). In the Columbia River, where Brown Bullheads were the primary catfish in the 19th and early 20th century, they did support a commercial fishery from 1894 to 1915, and were declared a gamefish (Lampman 1946). (Nowosad andTaylor 2012; Dextrase and Mandrak 2012).

Ecological Impacts

Although widely introduced, few specific negative impacts are reported, but they are still often regarded as an undesirable invasive species (Invasive Species Specialist Group 2018). On Vancouver Island, Canada, predation on eggs by Brown Bullhead has led to extinction of four endemic stickleback species pairs (Gasterosteus spp.) (Dextrase and Mandrak 2006). In experiments with fishes from the Fraser River, British Columbia, the presence of Brown Bullheads caused reduced growth and mortality of Brassy Minnows (Hybognathus hankinsoni) from an isolated, disjunct native population. In these experiments the reduced growth was presumed to be due to competition and aggression of Brown Bullheads (Nowosad and Taylor 2013). In Europe, nest guarding, and territoriality is an unusual habit in European fishes, and deprives native species of space for foraging.

Regional Impacts

P090San Francisco BayEconomic ImpactFisheries
Brown Bullheads are a popular pan-sized sport fish in the Delta (Moyle 2002), but they do not appear to be specifically targeted by fishers,
P260Columbia RiverEconomic ImpactFisheries
Brown Bullheads are a popular pan-sized sport fish in the Columbia River but they do not appear to be specifically targeted by fishers, There was a commercial fishery for catfish (mostly Brown Bullhead) from 1890 to 1913, after which, it was declared a game fish by the state legislature (Lampman 1946).
CACaliforniaEconomic ImpactFisheries
Brown Bullheads are a popular pan-sized sport fish in the Delta (Moyle 2002), but they do not appear to be specifically targeted by fishers,

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P260 Columbia River 1894 Def Estab
P090 San Francisco Bay 1874 Def Estab
N010 Passamaquoddy Bay 0 Native Estab
N020 Englishman/Machias Bay 0 Native Estab
N030 Narraguagus Bay 0 Native Estab
N036 _CDA_N036 (Maine Coastal) 0 Native Estab
N040 Blue Hill Bay 0 Native Estab
N050 Penobscot Bay 0 Native Estab
N090 Kennebec/Androscoggin River 0 Native Estab
N060 Muscongus Bay 0 Native Estab
N070 Damariscotta River 0 Native Estab
N080 Sheepscot Bay 0 Native Estab
N110 Saco Bay 0 Native Estab
N100 Casco Bay 0 Native Estab
N116 _CDA_N116 (Piscataqua-Salmon Falls) 0 Native Estab
N130 Great Bay 0 Native Estab
N125 _CDA_N125 (Piscataqua-Salmon Falls) 0 Native Estab
N150 Merrimack River 0 Native Estab
N160 Plum Island Sound 0 Native Estab
N170 Massachusetts Bay 0 Native Estab
N180 Cape Cod Bay 0 Native Estab
N185 _CDA_N185 (Cape Cod) 0 Native Estab
N195 _CDA_N195 (Cape Cod) 0 Native Estab
M010 Buzzards Bay 0 Native Estab
M020 Narragansett Bay 0 Native Estab
M026 _CDA_M026 (Pawcatuck-Wood) 0 Native Estab
M040 Long Island Sound 0 Native Estab
M060 Hudson River/Raritan Bay 0 Native Estab
NA-S3 None 0 Native Estab
M070 Barnegat Bay 0 Native Estab
M080 New Jersey Inland Bays 0 Native Estab
M090 Delaware Bay 0 Native Estab
M130 Chesapeake Bay 0 Native Estab
S010 Albemarle Sound 0 Native Estab
S020 Pamlico Sound 0 Native Estab
S030 Bogue Sound 0 Native Estab
S040 New River 0 Native Estab
S050 Cape Fear River 0 Native Estab
S060 Winyah Bay 0 Native Estab
S070 North/South Santee Rivers 0 Native Estab
S080 Charleston Harbor 0 Native Estab
S110 Broad River 0 Native Estab
S100 St. Helena Sound 0 Native Estab
S120 Savannah River 0 Native Estab
S130 Ossabaw Sound 0 Native Estab
S140 St. Catherines/Sapelo Sounds 0 Native Estab
S160 St. Andrew/St. Simons Sounds 0 Native Estab
S150 Altamaha River 0 Native Estab
S170 St. Marys River/Cumberland Sound 0 Native Estab
S175 _CDA_S175 (Nassau) 0 Native Estab
S180 St. Johns River 0 Native Estab
S190 Indian River 0 Native Estab
S183 _CDA_S183 (Daytona-St. Augustine) 0 Native Estab
S196 _CDA_S196 (Cape Canaveral) 0 Native Estab
S200 Biscayne Bay 0 Native Estab
G010 Florida Bay 0 Native Estab
G020 South Ten Thousand Islands 0 Native Estab
G030 North Ten Thousand Islands 0 Native Estab
G045 _CDA_G045 (Big Cypress Swamp) 0 Native Estab
G050 Charlotte Harbor 0 Native Estab
G070 Tampa Bay 0 Native Estab
G074 _CDA_G074 (Crystal-Pithlachascotee) 0 Native Estab
G078 _CDA_G078 (Waccasassa) 0 Native Estab
G086 _CDA_G086 (Econfina-Steinhatchee) 0 Native Estab
G090 Apalachee Bay 0 Native Estab
G080 Suwannee River 0 Native Estab
G110 St. Andrew Bay 0 Native Estab
G100 Apalachicola Bay 0 Native Estab
G120 Choctawhatchee Bay 0 Native Estab
G130 Pensacola Bay 0 Native Estab
G150 Mobile Bay 0 Native Estab
G160 East Mississippi Sound 0 Native Estab
LMANIT Lake Manitoba 0 Native Estab
GL-I Lakes Huron, Superior and Michigan 0 Native Estab
GL-III Lake Ontario 0 Native Estab
GL-II Lake Erie 0 Native Estab
P210 Yaquina Bay 1990 Def Estab
P160 Coquille River 2001 Def Estab
S090 Stono/North Edisto Rivers 0 Native Estab
P298 _CDA_P298 (Fraser) 0 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


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Matern, Scott; Meng, Lesa; Pierce, Leslie C. (2001) Native and introduced larval fishes of Suisun Marsh, California: the effects of freshwater flow., Transactions of the American Fisheries Society 130: 750-765

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Sytsma, Mark D.; Cordell, Jeffrey R.; Chapman, John W.; Draheim, Robyn, C. (2004) <missing title>, Center for Lakes and Reservoirs, Portland State University, Portland OR. Pp. <missing location>

USGS Nonindigenous Aquatic Species Program 2003-2024 Nonindigenous Aquatic Species Database.

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Wright, Rosalind; et al. (2022) First direct evidence of adult European eels migrating to their breeding place in the Sargasso Sea, Scientific Reports 3,2(25362): Published online