Burbot, (Cohen, et al., 1990), are a holarctic species native to the cold fresh waters of the Nearctic and Palearctic regions found between 40 and 70 degrees North latitudes.
Burbot are demersal fish found in deep temperate lake bottoms and slow moving cold river bottoms between 4 and 18 degrees C (Riede 2004; Cohen et al. 1990). Primarily found at depths ranging from 1 to 700 m, these fish prefer fresh waters but are also found in some brackish water systems (Cohen et al. 1990). These fish often dwell among benthic refugia such as roots, trees, rocks, and dense vegetation (Billard 1997). (Billard, 1997; Cohen, et al., 1990; Morrow, 1980; Riede, 2004; Scott and Crossman, 1973)
Burbot are large fish known to grow to as much as 1.5 m in length and 34 kg in mass (Morrow 1980). These fish are yellow, light tan, or brown with dark brown or black patterning on the body, head and most fins. The underbelly and pectoral fins are pale to white (Cohen et al. 1990; Morrow 1980). The first dorsal fin is short and is followed by a long second dorsal fin at least 6 times the length of the first and joined to a rounded caudal fin (Morrow 1980). Burbot have neither dorsal nor anal spines and have 67 to 96 soft dorsal rays, and 58 to 79 soft anal rays (Cohen et al. 1990). Gill rakers are short, pectoral fins are rounded, and caudal fins have 40 rays (Morrow 1980). Like other cods, burbot are also characterized by a single barbel located on the chin (Morrow 1980). (Cohen, et al., 1990; Morrow, 1980)
Burbot eggs hatch in the spring between April and June depending on location (Bjorn 1940; Cohen 1990). Time to hatching is dependent on temperature as well as the particular population and eggs usually take between 30 and 70 days to hatch (MacCrimmon 1959; Bjorn 1940). In four weeks larval burbot increase in length from less than 1 cm to over 2 cm (Ghan and Sprules 1993). Burbot in Lake Superior exhibited very fast growth rates during the first two growing seasons, attaining 42% of total length after 10 growing seasons (Bailey 1972). (Bailey, 1972; Bjorn, 1940; Cohen, et al., 1990; Ghan and Sprules, 1993; MacCrimmon, 1959)
In the Vilyuy River Basin, Siberia, burbot attain sexual maturity in their 7th or 8th year, with males usually maturing 1 year before females (Kirillov 1988). In Lake Superior, burbot as young as one year old were sexually mature (Bailey 1972). Though sexually mature specimens were found for both sexes in year 1 and older age classes, there was a higher proportion of sexually mature males until year 5 when all specimens of both sexes were sexually mature (Bailey 1972). Activity of burbot increases in autumn as energy reserves are concentrated on the growth and development of gonads for the winter spawning season (Kirillov 1988). Maturation of the gonads in both sexes occurs about 4 months after the fall peak in nutritional reserves (Pulliainen and Korhonen 1990). (Bailey, 1972; Kirillov, 1988; Pulliainen and Korhonen, 1990)
Burbot breed once per year in the winter, migrating to shallow water or to a smaller stream to spawn (Cohen 1990). Burbot move to spawning areas individually and males tend to arrive before females (Morrow 1980). Spawning occurs during the night when individuals form a globular mass, each fish pushing toward the center and releasing eggs or sperm (MacCrimmon 1959; Cahn 1936). Postspawning runs upstream have been observed, most likely for feeding (MacCrimmon 1959). (Cahn, 1936; Cohen, et al., 1990; MacCrimmon, 1959; Morrow, 1980)
Burbot are potamodromous, migrating up tributaries or smaller stream reaches to spawn (Cohen 1990). They spawn in winter, laying their eggs in shallow water to hatch during the spring (Kirillov 1988). Fecundity varies geographically from slightly above 100,000 in specimens from Wyoming to over 3 million elsewhere in their range (Bailey 1972). Average fecundity ranges from 700,000 to 800,000 eggs (Kirillov 1988; Bailey 1972). Eggs are yellow, amber, or orange in color, spherical, and rest on the substrate (Koli 1990; Bjorn 1940). Eggs usually hatch in two to four months.
Burbot may take several years to become sexually mature. Present literature indicates a certain proportion of burbot populations fail to mature during each breeding season (Pulliainen and Korhonen 1990). Some studies have also suggested that burbot may take one or two years to restore nutritional reserves after a spawning event (Pulliainen and Korhonen 1990). (Bailey, 1972; Bjorn, 1940; Cohen, et al., 1990; Kirillov, 1988; Koli, 1990; Pulliainen and Korhonen, 1990)
Burbot are broadcast spawners and provide no parental care. Parental investment in burbot is characterized by an increased metabolic activity level and food consumption rates in the fall in order to contribute to the growth and maturation of gonads in both male and females over a four month period preceeding spawning events (Pulliainen and Kohonen 1990; Kirrilov 1988). It has been suggested that burbot may require one to two years to replenish their nurtritional reserves after each spawning event, but no further information on this topic was available (Pulliainen and Kohonen 1990). (Kirillov, 1988; Pulliainen and Korhonen, 1990)
The lifespan of burbot has been known to be as high as 20 years, though studies of natural populations rarely see individuals exceeding 10 to 12 years of age (Cohen 1990; Kirillov 1988; Bailey 1972). Incidence of older and larger individuals in nearctic regions may exceed that of older individuals in palearctic regions due to the absence of an established fishery, sport or otherwise, in North America where one thrives in Eurasia (Kirillov 1988). (Bailey, 1972; Cohen, et al., 1990; Kirillov, 1988)
Burbot are opportunistic piscivores with a diverse diet. They hide amongst available refugia in their epibenthic habitat such as rocks and fallen logs, and use ambush tactics to capture prey (Kahilainen and Lehtonen 2003). They are crepuscular or nocturnal and seek shallow water to feed. During times of low activity, they congregate in deep holes (Riede 2004; Morrow 1980; Scott and Crossman 1973). In the winter, these fish migrate upstream and form spawning aggregations (Cohen 1990). (Cohen, et al., 1990; Kahilainen and Lehtonen, 2003; Morrow, 1980; Riede, 2004; Scott and Crossman, 1973)
Burbot perceive chemical, tactile, visual, and acoustic stimuli, as do most fish. Though burbot and northern pike exhibit similar hunting strategies, burbot appear to rely less on sight than pike (Kahilainen and Lehtonen 2003). (Kahilainen and Lehtonen, 2003; von der Emde, 2004)
Newly hatched burbot are completely planktivorous, and remain so even when they are no longer gape limited (Ghan and Sprules 1993). Diet of larval burbot is dominated by rotifer species for the first two weeks. Diet then shifts to slightly larger nauplii, changing further during week four to cycloid copepods, daphnia, and calanoid copepods (Ghan and Sprules 1993). Juveniles have a diet of molluscs and insect larvae (Tolanen et al. 1999). Adult burbot are piscivorous and consume over 99% fish by mass in Lake Superior (Bailey 1972). Though burbot are always a primarily piscivorous fish, their diet changes seasonally and in response to competition. After the winter months, Tolanen et al. (1999) found that burbot ate a much higher proportion of aquatic invertebrates, namely crustaceans in the early summer and oppossum shrimp in the fall. In the Vilyusk resevoir, diet overlap with pike forces burbot to broaden their diet breadth to include more benthic invertebrates (Kirillov 1988). In addition to fish and invertebrates, Bailey (1972) also found rocks, wood chips, plastic, and other inert materials in burbot stomachs, indicating that burbot feeding habits were somewhat indiscriminate. (Bailey, 1972; Ghan and Sprules, 1993; Kirillov, 1988; Tolanen, et al., 1999)
Northern pike are known to prey on burbot where the two species coexist (Schwalme 1992). Smelt and yellow perch prey on larval and juvenile individuals (Scott and Crossman 1973). Humans also exert predation pressure on burbot through commercial and sport fisheries (Cohen 1990; Kirillov 1988). In the Great Lakes, the sea lamprey, Petromyzon marinus, is also known to prey on burbot (Smith 1971). Burbot rely on their cryptic habits and coloration to avoid predators. (Cohen, et al., 1990; Kirillov, 1988; Schwalme, 1992; Scott and Crossman, 1973; Smith, 1971)
Burbot are an important commercial fishery in parts Eurasia where they are used as a source of oil, the flesh is eaten, and liver is sold smoked or canned (Kirillov 1988; Scott and Crossman 1973). Burbot are also processed into fish meal (Scott and Crossman 1973). Because of slow movements and nocturnal habits, little or no sport fishery exists in North America (Cohen 1990). (Cohen, et al., 1990; Kirillov, 1988; Scott and Crossman, 1973)
There are no known negative effects of burbot on humans.
Burbot are near extinction in the Kootnai river in Idaho and British Columbia due to construction of the Libby dam in Idaho. Efforts to bring back the population are ongoing (Kootnai River Fisheries Investigation 2000). Burbot are stocked where commercial fisheries exist in Europe (Kirillov 1988). ("Kootenai River Fisheries Investigation: Stock Status of Burbot", 2000; Kirillov, 1988)
Allison Poor (editor), University of Michigan-Ann Arbor.
Greg Jacobs (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.
Found in northern North America and northern Europe or Asia.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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