Esociformes

(Pikes and mudminnows)

Class Actinopterygii

Order Esociformes

Number of families 1 or 2

Evolution and systematics

Three key questions to consider regarding the evolution of esociforms are: When did they originate? What other group of fishes is their closest relative? And, what are the evolutionary relationships among esociform species?

As of 2002, the earliest evidence of esociform fishes in the fossil record was in the form of fragmentary fossils found in deposits dating to the Upper Cretaceous from Alberta, Canada. The evidence consists of numerous fossilized fragments of bones that form the mouth skeleton, which displays a distinctive form of tooth attachment that is characteristic of living esociform species. Almost complete fossils of esociform fishes are found in Paleocene deposits from Alberta and Eocene deposits from Wyoming, United States. These fossils are extremely similar to living species of Esox. The fossil evidence suggests that esociform fishes belong to an ancient fish lineage that is more than 70 million years old.

Unfortunately, scientists have a poor understanding of the relationship of esociforms to other fish groups of similar age. The many primitive anatomical features that characterize esociforms hinder the development of a satisfactory theory on the classification of esociforms, despite a long history of phylogenetic studies on this area of fish evolution. Systematic studies based on anatomical comparisons have yielded tentative conclusions based on scant evidence. Studies based on comparisons of genetic sequences have produced the most strongly supported hypothesis of esociform relationships. These studies show unequivocal support for a close evolutionary relationship between the fishes in the order Salmoniformes (i.e., salmons, trouts, chars) and the esociforms. However, a consensus hypothesis is not available.

The order Esociformes includes four genera and 10 to 12 species, depending on the validity of two species described in 1982 from Siberia. The four genera of Esociformes are:

• Dallia (Alaska blackfish or dogfish)
• Esox (Northern pike, muskellunge, and pickerels)
• Novumbra (Olympic mudminnow)
• Umbra (European, central, and eastern mudminnows)

Until the late 1990s, esociform genera were divided into two families: Esocidae, for the genus Esox; and Umbridae, for the remaining three genera, which are collectively termed the mudminnows. This classification conflicts with molecular data first reported in 2000, which showed that these two families do not represent natural evolutionary groups. The molecular evidence suggests that the genera Esox and Novumbra are the closest evolutionary relatives, and that Umbra is the most primitive of the four esociform genera. In light of this evidence, the traditional two-family division of esociforms should be disregarded. A one-family scheme is followed in this chapter but, as of 2002, there was no general agreement on the classification of esociform genera.

Physical characteristics

One striking characteristic of all living esociforms is the posterior placement of the dorsal fin, which is located nearly opposite the anal fin in all species. Esociforms have elongate bodies with round cross sections. Esox species are further characterized by a flattened and elongated snout, which somewhat resembles a duck's bill.

Most species are small or medium sized; but Esox includes very significant exceptions. For example, individuals of E. masquinongy may reach over 5 ft (1.6 m) in length and weigh more than 66 lb (30 kg). At the other end of the scale, individuals of the four species in Novumbra and Umbra rarely reach 4 in (10 cm) and weigh less than 1 oz (28.3 g). In light of their marked contrast in size, it is interesting to note that Esox and Novumbra are thought to be very close relatives.

The coloration of esociforms is varied, but markings or mottled patterns on brown or olive green backgrounds are a common feature. A mottled coloration pattern in the densely vegetated habitats that esociforms favor likely hinders their detection by prey and/or predators. Males of some species show intensified coloration during the breeding season, with attractive iridescent hues on the body and fins.

Distribution

Living species of esociforms are found in all major Northern Hemisphere landmasses, with the exception of Greenland. North America is home to eight species of esociforms, three are found in northern Asia, and two inhabit European waters. The fossil record shows that the diversity of species of esociforms in Europe and Asia has been higher in the past. However, as of 2002, there was no evidence to indicate major changes in the global distribution of the order over its evolutionary history.

There have been changes in the distribution of some esociform species due to human intervention. The ranges of species in Novumbra and Umbra have undergone attrition due to habitat destruction. In contrast, the natural distributions of some Esox species have been expanded by human intervention because of their value as sport fishes.

Habitat

The understanding of the biology of esociforms is much more extensive for members of the genus Esox because these species are important in recreational fishing. However, the few studies conducted on the biology of the other esociform species point to broad similarities among all members of the order. Adults of the larger species of Esox move freely between shore and open water habitat. All esociforms show a similar preference for still or slow-moving water where dense vegetation allows them a place to hide. Other than dense vegetation, mudminnows seek areas with thick and loose muddy substrate, into which they quickly dive when startled. In addition, mudminnows have modified areas of the gut and swim bladder to extract oxygen from ingested atmospheric air. This allows them to withstand the widely fluctuating oxygen levels that may be associated with the heavy vegetation and rich organic matter substrate characteristic of their habitat.

Behavior

Outside the breeding season, esociforms are solitary and sedentary. They are most often found hovering among vegetation using elegant and economical pectoral and medial-fin movements to remain in place, with occasional pelvic-fin motions to correct body orientation. From this stance, the pikes wait for their prey, which they capture with a fast strike. Mudminnows may perch on the vegetation or rest on the substrate, eliminating the need for any fin movement. When dissolved oxygen levels are low, mudminnows occasionally swim up to the water surface and gulp air.

Feeding ecology and diet

Esociformes are carnivorous, predatory fishes. All Esox species prey most commonly on fishes, including smaller individuals of their own species. The larger species may also prey on frogs, waterfowl, and small mammals; their diets seem to be limited only by the size of the potential prey item and the opportunity for its capture. The mudminnows and the Alaska blackfish are also carnivorous, but due to their small size their diet consists almost entirely of aquatic invertebrates and, very rarely, juvenile fish.

Adult northern pike and muskellunge have only a few opportunistic natural predators, including bears, otters, and large birds of prey. Juveniles and fry of species of Esox are commonly preyed upon by larger members of the genus and other predatory fishes that share their habitat (e.g., centrarchid basses). The blackfish and the Olympic mudminnow have few predators because they occupy areas with few other species and are often found among thick vegetation that prevents terrestrial predators from targeting them. Pikes, pickerels, and other piscivorous fishes prey on mudminnows of the genus Umbra.

Reproductive biology

Most esociforms spawn early in the spring when water temperatures begin to rise. Some populations must undertake a migration to reach the spawning grounds. There is no evidence of nest building, but there are reports of territoriality around the spawning site in species of Novumbra and Umbra. Spawning most often involves one female and a few to several males. In some species, the males court the females through swimming displays or aggression. Egg deposition is usually preceded by exaggerated swimming motions and side-to-side contact. Eggs may stick to vegetation or drop to the ground. Fry do not receive parental care.

Conservation status

Habitat destruction is the main threat to populations of esociforms. Mudminnows are particularly vulnerable to this threat because they occur in areas with large human populations, and their habitat preference is not compatible with traditional land-development practices. The European mudminnow (Umbra krameri) is classified as Vulnerable by the IUCN, while the Olympic mudminnow (Novumbra hubbsi) is classified as Lower Risk/Near Threatened. Due to the interest of recreational anglers on all species of Esox, management policies and fishing regulations are in place to ensure stable populations.

Significance to humans

The greatest interest of humans in these fishes in modern times is limited to those species, all of which are members of the genus Esox, targeted by recreational anglers. There has been sporadic interest by aquarium enthusiasts in various mudminnows. Historically, some human populations indigenous to Siberia and Alaska have included blackfish in their diet.

Species accounts

List of Species

Alaska blackfish

Dallia pectoralis

family

Esocidae

taxonomy

Dallia pectoralis Bean, 1880, Saint Michaels, Alaska, United States.

other common names

English: Dogfish; French: Dallia; German: Fächerfisch; Russian: Chernaya ryba.

physical characteristics

Length 1.9–6.3 in (4.8–16 cm); specimens as large as 13 in (33 cm) have been recorded; males reach larger sizes due to their longer lifespan. Stout head, well-developed fanlike pectoral fins, and much-reduced pelvic fins. Usually with a brown mottled pattern on a light cream background and light margins on the fins.

distribution

Lowlands of northern and western Alaska and the Chukot Peninsula of eastern Siberia. Introduced and established in Anchorage and St. Paul Island. Populations of Dallia that inhabit Arctic drainages of eastern Siberia may represent two different species of this genus.

habitat

In the spring and summer, occurs in shallow ditches and lakeshores with little or no water movement and thick vegetation. In winter, may move to deeper areas to avoid freezing.

behavior

Mostly unknown. Their ability to tolerate extremely low temperatures is well known but not thoroughly understood; behavioral and/or physiological adaptations are probably involved. A gas-exchange organ associated with the esophagus allows them to obtain oxygen from gulped air, thus allowing them to occupy waters with low concentration of dissolved oxygen.

feeding ecology and diet

Preys predominantly on crustaceans (caldocerans, copepods, and ostracods) and aquatic insect larvae. Other aquatic invertebrates and, rarely, fish complement the diet.

reproductive biology

The timing of spawning varies, depending on seasonal conditions at a given location. A population near Fairbanks, Alaska, spawns during May and June. Some populations undertake a migration to the spawning grounds in spring when thawing makes these areas available. Mature females carry 40–300 sticky, transparent eggs. Little is known about spawning behavior.

conservation status

Not threatened. Widespread and abundant in their native range. Their remote distribution protects their habitat from destruction by human action. As of 2002 in the United States, it was illegal to transport live blackfish out of their native range without a permit.

significance to humans

Some indigenous communities have relied heavily on blackfish for food for themselves and their dogs. The nutritive value of blackfish was greatest in the winter when other sources of protein were scarce and these communities faced starvation. In modern times human consumption of blackfish has decreased, probably as a result of year-round availability of other foods.

Northern pike

Esox lucius

family

Esocidae

taxonomy

Esox lucius Linnaeus, 1758, Europe.

other common names

English: Jack, luce; French: Brochet; German: Hecht; Russian: Shchuka; Spanish: Lucio.

physical characteristics

Standard length 35.4 in (90 cm); standard weight 24.2 lb (11 kg); flattened, elongate snout, scales on cheek and operculum. Long, cylindrical body with irregular yellow spots on a silvery green background that is lighter towards the belly. Stoutness of body varies depending on growing conditions, with better conditions resulting in deeper-bodied fish.

distribution

Northern North America, Europe, and Asia. Introduced by humans to Africa, Ireland, and Spain.

habitat

Prefers cool lakes, ponds, and slow-moving rivers with abundant vegetation. Young and smaller adults occupy shallow shore areas and move to greater depths as they grow.

behavior

Solitary outside the breeding season. Hovers almost motionless among vegetation in wait for unsuspecting prey. May remain in same location for long periods of time if food is plentiful, otherwise will range over large distances in habitat with low prey density.

feeding ecology and diet

Voracious sit-and-wait predator; feeds on any animal large enough to be worth the effort and small enough to be subdued. Fish are the largest component of the diet. Fry feed on invertebrates until they are able to take fish. Fry and juveniles fall prey to larger individuals of the species, as well as to frogs and large aquatic insects. Adults are vulnerable to osprey and other large fish-eating birds, as well as otters, bears, and commercial and recreational fishing.

reproductive biology

Spawning occurs in early spring. Males and females move close to shore or from streams to marshy areas. One female and a few smaller males swim into shallow vegetated areas. Females release a small number of eggs, which are immediately fertilized by attendant males. Egg release is repeated a varying number of times. Females may carry as many as 250,000 eggs. Both males and females may spawn with different mates during a spawning season. Adults do not guard spawning sites or provide care to the young.

conservation status

Not threatened. Many populations are managed to maintain strong recreational fishing. Habitat destruction is a threat in some parts of their distribution, but worldwide they are not at risk.

significance to humans

In modern times, they are highly valued sport fishes and the focus of a recreational fishery of substantial economic importance. In the past, they were also valued as food fishes, and a sizable commercial fishery existed. Some praise the flavor of their flesh, but demand is not widespread and the commercial fishery is small.

Muskellunge

Esox masquinongy

family

Esocidae

taxonomy

Esox masquinongy Mitchill, 1824, Lake Erie, North America.

other common names

English: Lunge, muskie, mascalonge.

physical characteristics

Standard weight 33 lb (15 kg); scales only on upper half of cheek and operculum. Prominent sensory pores on lower jaw. Dark spots or mottled markings on a silver or light green body, but color variation exists between populations in different parts of their distribution and markings may be absent.

distribution

Northeastern North America; centered around Great Lakes region.

habitat

As with E. lucius, prefers slow-moving or still waters with abundant vegetation, but with slightly warmer water temperatures.

behavior

Mostly sedentary among vegetation. Hovers among aquatic vegetation, striking at prey with a fast, powerful lunge. For unknown reason, sometimes floats just beneath the water surface with the back exposed to the air.

feeding ecology and diet

Voracious predators; predominantly feed on fishes, but are known to eat crayfishes, frogs, waterfowl, and small mammals. Fry begin eating small invertebrates until they are able to capture larger prey. Fry are often eaten by E. lucius fry, which hatch some weeks earlier. Subadults are vulnerable to ospreys and other large fish-eating birds, as well as otters, bears, and commercial and recreational fishing. Large adults have no predators other than humans.

reproductive biology

Spawns in spring when water temperature reaches 49–59°F(9.4–15°C). Similar courtship and spawning behavior as E. lucius, but avoids areas where that species spawns by releasing eggs in deeper water. In nature, these two species form sterile hybrids that are known as tiger muskies.

conservation status

Not threatened. However, this species is rare in some areas and these populations are protected. Recreational fishing is strictly managed.

significance to humans

Numerous businesses profit from activities related to recreational angling in Canada and the United States. Winter fishing for these and other fishes through the ice using spears is a valued part of the cultural tradition of some Native American communities, and is still practiced in part of Wisconsin.

Olympic mudminnow

Novumbra hubbsi

family

Esocidae

taxonomy

Novumbra hubbsi Schultz, 1929, near Satsop, Washington, United States.

other common names

None known.

physical characteristics

Length 1–3.4 in (2.5–8.5 cm); light to dark brown with light green vertical stripes along the entire length of the fish. Dark vertical bar across eye. Males develop a striking breeding coloration consisting of green to blue iridescent vertical stripes on an almost black background.

distribution

Restricted to lowlands of south and west drainages of the Olympic Peninsula in Washington State, United States, and a few drainages of the Puget Sound. Not known whether the Puget Sound populations are native or introduced.

habitat

Ponds, ditches, or creeks with still or slow-moving water, abundant submerged vegetation, and, usually, a thick layer of loose mud substrate

behavior

Can survive in water with low oxygen content and under a wide range of temperatures, but shows little tolerance for salinity.

feeding ecology and diet

Feeds on aquatic invertebrates; primarily ostracods, isopods, worms and aquatic insects. Tends to coexist with only a few other fish species; primarily the reticulate sculpin (Cottus perplexus) and the three-spined stickleback (Gasterosteus aculeatus). Reticulate sculpins may prey on juvenile mudminnows. Although vulnerable to fish-eating birds, adults appear to have few predators.

reproductive biology

Peak spawning occurs in April and May, but can take place from November to June with a lull in the winter. Males defend territories and perform a courtship display for passing females. Mating pairs wiggle in place side by side and spawn repeatedly, releasing a few eggs at a time. Eggs stick to vegetation or the substrate. Fry remain in place for about one week before dispersing. Parental care has not been documented.

conservation status

Listed as Lower Risk/Near Threatened by the IUCN, as habitat destruction is a significant threat due to a very restricted distribution. The state of Washington gives the species special management consideration.

significance to humans

None known.

European mudminnow

Umbra krameri

family

Esocidae

taxonomy

Umbra krameri Walbaum, 1792, Danube River, Europe.

other common names

German: Hundsfisch; Hungarian: Lápi póc; Russian: Evdoshka; Ukrainian: Boboshka, lezheboka.

physical characteristics

Length 2–3.5 in (5–9 cm); elongated body is slightly flattened dorsoventrally. Dorsal fin has almost rectangular profile. Drab brown coloration with a light horizontal stripe through the middle of the body.

distribution

Lowlands of the Danube River drainage from Vienna to the Black Sea, as well as the Prut and Dniester Rivers.

habitat

Oxbow lakes, ditches, and ponds with dense vegetation and debris.

behavior

Few field studies have examined behavior.

feeding ecology and diet

Feeds mainly on aquatic crustaceans and insect larvae; rarely fish fry and vegetation. Main predators are piscivorous water-fowl, predatory fishes (including young of E. lucius), and large insects.

reproductive biology

Spawning takes place from February to April. Several males pursue ripe females, which become progressively more receptive to their attention. Females that are ready to spawn find a suitable patch of vegetation and swim into it, followed by several attentive males. Males position themselves next to the females and eggs and sperm are released. The eggs may stick to the vegetation or sink to the bottom. After an interval of varying length, the process is repeated until the female has exhausted her egg supply. The female subsequently guards her spawning territory, but does not seem to take special care of the eggs or fry.

conservation status

Habitat destruction has led to extirpation from a large part of the known historical distribution. Flood control of rivers and wetland development destroy its required habitat. Pollution affects all drainages where it exists. As a result, classified as Vulnerable by the IUCN.

significance to humans

Of no interest to commercial or recreational fisheries. In the past, used to feed livestock and as crop fertilizer. Because they represent a unique evolutionary lineage, countries where viable populations exist use this species to stimulate wildlife awareness and education.

Central mudminnow

Umbra limi

family

Esocidae

taxonomy

Hydrargira limi Kirtland, 1840, Yellow Creek, Trumbull County, Ohio, United States.

other common names

English: Dogfish, mudfish, mudpuppy; German: Amerikanischer Hundsfisch.

physical characteristics

Length 1.6–3.9 in (4–10 cm); short cylindrical body. Dark brown to green, with lighter, irregular vertical stripes along the length of the body.

distribution

Centered around the Great Lakes region from northern Tennessee, United States, to southern Manitoba and Quebec, Canada.

habitat

Still or slow-moving water in ponds and ditches with a thick layer of mud on the bottom and abundant aquatic vegetation.

behavior

Little information available. Sedentary in vegetation or resting on substrate, moving only to forage or to gulp air from surface. Capable of obtaining oxygen from air through the swim bladder. Evades predators by diving into the muddy substrate.

feeding ecology and diet

Carnivorous; feeds on aquatic invertebrates, particularly crustaceans and insect larvae. Important predators are juveniles of Esox species. Also vulnerable to water snakes and fish-eating birds.

reproductive biology

Spawning takes place in the early spring on flooded banks. Mature females carry 200–2,200 eggs. Eggs are sticky and deposited in dense vegetation, where they hatch after about six days. Fry are not guarded or cared for by parents.

conservation status

Not listed by IUCN. Rare in the western and southern limits of their distribution, probably as a result of habitat alteration. Widespread and abundant where their habitat is available. Habitat destruction by flood control and draining of wetlands is an ongoing threat.

significance to humans

Of no interest as a food fish. Because they are hardy, considered good for bait in some regions, but drab coloration reduces their value to the angler. Of some interest to aquarists.

Resources

Books

Craig, John F., ed. Pike Biology and Exploitation. New York: Chapman & Hall, 1996.

Morrow, James E. "Mudminnows and Blackfish." In The Freshwater Fishes of Alaska. Anchorage: Alaska Northwest Publishing Co., 1980.

Scott, William B., and E. D. Crossman. "Mudminnows: Umbridae." In Freshwater Fishes of Canada. Oakville, Ontario: Galt House Publishing, 1998.

——. "Pikes: Esocidae." In Freshwater Fishes of Canada. Oakville, Ontario: Galt House Publishing, 1998.

Periodicals

Grande, L. "The First Esox (Esocidae: Teleostei) from the Eocene Green River Formation, and a Brief Review of Esocid Fishes." Journal of Vertebrate Paleontology 19 (1999): 271–292.

López, J., T. Pietsch, and P. Bentzen. "Phylogenetic Relationships of Esocoid Fishes (Teleostei) Based on Partial Cytochrome b and 16S Mitochondrial DNA Sequences." Copeia (2000): 420–431.

Martin-Bergmann, K. A., and J. H. Gee. "The Central Mudminnow, Umbra limi (Kirtland), a Habitat Specialist and Resource Generalist." Canadian Journal of Zoology 63(1985): 1,753–1,764.

Mikschi, E., J. Wanzenböck, compilers. "Proceedings of the First International Workshop on Umbra krameri Walbaum, 1792." Annalen des Naturhistorischen Museums in Wien Serie B Botanik und Zoologie 97B (1995): 437–508.

Organizations

Muskies Canada Sport Fishing and Research, Inc.. P.O. Box 814, Station C, Kitchener, Ontario N2G 4C5 Canada. Web site: <http://www.trentu.ca/muskie/mc.html>

Other

"Alaska Blackfish." Alaska Department of Fish and Game, Wildlife Notebook Series [cited February 6, 2003]. <http://www.state.ak.us/local/akpages/FISH.GAME/notebook/fish/blackfsh.htm>

"Blackfish: A Cultural Mini-Unit." Alaska Native Knowledge Network [cited February 6, 2003]. <http://www.ankn.uaf.edu/UNITS/blackfish.html>

"The International Muskie Homepage." [cited February 6, 2003]. <http://www.trentu.ca/muskie/muskie.html>

"Understanding Northern Pike and Muskie." The Content Well [cited February 6, 2003]. <http://www.thecontentwell.com/Fish_Game/Northern_Pike/Pike_index.html>

Juan Andrés López, MS