Adult Burbot Research Articles

Larval morphology of North American burbot (Lota lota maculosa) from two spatially separated populations

Burbot (Lota lota) are a freshwater fish that exhibits a circumpolar distribution and is considered an indicator species for climate change. Adult burbot were artificially fertilized from the Sturgeon River, Michigan and eggs were incubated until hatch. For 10 weeks following hatch larvae were photographed, along with comparable samples from the Kootenai River, Idaho. Geometric morphology was used to quantify significant morphological differences between groups (n = 510). During the yolk sac stages, body shape near yolk sacs varied, likely linked to absorption differences. In preflexion and flexion stages, variable body shape in the mid-body region coincided to head and tail positions. Mean linear morphological measurement (n = 919) showed significant differences, indicating variability of size at stage between groups. Sturgeon River preflexion larvae growth patterns were variable and exhibited allometric growth in comparison to Kootenai River larvae. This suggests that development of critical structures occurs at different rates allowing for flexibility in habitat settlement or environmental conditions. Both groups showed isometric growth patterns in the flexion stage, indicating that critical structures have developed, marking an important ontogenetic shift. Variability in larval burbot hatching, morphology, and developmental rates is important to their persistence throughout North America.

Sampling techniques for burbot in a western non‐wadeable river

AbstractBurbot, Lota lota (L.), populations are declining throughout much of their native distribution. Although numerous aspects of burbot ecology are well understood, less is known about effective sampling techniques for burbot in lotic systems. Occupancy models were used to estimate the probability of detection () for three gears (6.4‐ and 19‐mm bar mesh hoop nets, night electric fishing), within the context of various habitat characteristics. During the summer, night electric fishing had the highest estimated detection probability for both juvenile (, 95% C.I.; 0.35, 0.26–0.46) and adult (0.30, 0.20–0.41) burbot. However, small‐mesh hoop nets (6.4‐mm bar mesh) had similar detection probabilities to night electric fishing for both juvenile (0.26, 0.17–0.36) and adult (0.27, 0.18–0.39) burbot during the summer. In autumn, a similar overlap between detection probabilities was observed for juvenile and adult burbot. Small‐mesh hoop nets had the highest estimated probability of detection for both juvenile and adult burbot (0.46, 0.33–0.59), whereas night electric fishing had a detection probability of 0.39 (0.28–0.52) for juvenile and adult burbot. By using detection probabilities to compare gears, the most effective sampling technique can be identified, leading to increased species detections and more effective management of burbot.

Winter feeding ecology and the importance of cannibalism in juvenile and adult burbot (Lota lota) from the Mackenzie Delta, Canada

The diet of adult burbot (Lota lota) collected from two locations in the Mackenzie Delta during the winter was characterized using stomach content and stable isotopes analysis (δ 13C and δ 15N). Burbot consumed mainly ninespine stickleback, juvenile northern pike, and conspecifics, with high δ 15N confirming long-term piscivory. Of the 66 adult burbot sampled, 530 juvenile burbot were enumerated from their stomachs, and from these, 50 juvenile burbot were counted. Many of these juveniles were undigested and were examined for diet content and stable isotopes. Juveniles primarily consumed invertebrates, however, piscivory was detected in young-of-the-year, with stickleback and conspecifics becoming more important as size increased, possibly resulting in competition with adults for small-size fish. δ 15N indicated juvenile burbot occupied a lower tropic level while δ 13C suggested differences in habitat properties between sites. Cannibalism was important to adult diet where the highest frequency of occurrence was 96%, with conspecifics accounting for 82 and 93% of diet items by number and weight, respectively. Cannibalism in burbot increased its trophic breadth and juvenile growth rate, and combined with the amount of conspecifics consumed possibly promoted population stability and coexistence with intraguild predators.

Females exceed males in mercury concentrations of burbot Lota lota.

Examination of differences in contaminant concentrations between the sexes of fish, across several fish species, may show clues for important behavioral and physiological differences between the sexes. We determined whole-fish total mercury (Hg) concentrations of 25 male and 25 female adult burbot Lota lota captured in Lake Erie during summer 2011 and of 14 male and 18 female adult burbot captured in Great Slave Lake (Northwest Territories, Canada) during winter 2013. On average, females had 22% greater Hg concentrations than males. This difference was probably not due to a greater feeding rate by females because results from previous studies based on polychlorinated biphenyl determinations of these same burbot indicated that males fed at a substantially greater rate than females. Based on our determinations of Hg concentrations in the gonads and somatic tissue of 5 ripe females and 5 ripe males, this difference was not attributable to changes in Hg concentration immediately after spawning due to the release of gametes. Furthermore, bioenergetics modeling results from previous studies indicated that growth dilution would not explain any portion of this observed difference in Hg concentrations between the sexes. We therefore conclude that this difference was most likely due to a substantially faster rate of Hg elimination by males compared with females. Male burbot exhibit among the greatest gonadosomatic indices (GSIs) of all male fishes, with their testes accounting for between 10 and 15% of their body weight when the fish are in ripe condition. Androgens have been linked to enhanced Hg-elimination rates in other vertebrates. If androgen production is positively related to GSI, then male burbot would be expected to have among the greatest androgen levels of all fishes. Thus, we hypothesize that male burbot eliminate Hg from their bodies faster than most other male fishes and that this explains the greater Hg concentration in females compared with males.

Detection Probabilities of Electrofishing, Hoop Nets, and Benthic Trawls for Fishes in Two Western North American Rivers

Abstract Research comparing different sampling techniques helps improve the efficiency and efficacy of sampling efforts. We compared the effectiveness of three sampling techniques (small-mesh hoop nets, benthic trawls, boat-mounted electrofishing) for 30 species in the Green (WY, USA) and Kootenai (ID, USA) rivers by estimating conditional detection probabilities (probability of detecting a species given its presence at a site). Electrofishing had the highest detection probabilities (generally greater than 0.60) for most species (88%), but hoop nets also had high detectability for several taxa (e.g., adult burbot Lota lota, juvenile northern pikeminnow Ptychocheilus oregonensis). Benthic trawls had low detection probabilities (<0.05) for most taxa (84%). Gear-specific effects were present for most species indicating large differences in gear effectiveness among techniques. In addition to gear effects, habitat characteristics also influenced detectability of fishes. Most species-specific habitat relationships were idiosyncratic and reflected the ecology of the species. Overall findings of our study indicate that boat-mounted electrofishing and hoop nets are the most effective techniques for sampling fish assemblages in large, coldwater rivers.

Song of the burbot: Under-ice acoustic signaling by a freshwater gadoid fish

Burbot (Lota lota) are northern freshwater gadoid fish that spawn under ice-cover, making their reproductive behavior largely unknown to science. Some members of the cod family vocalize as part of their mating system. These calls are produced by rapidly contracting drumming muscles on their swim bladders. Burbot also possess drumming muscles, like their marine counterparts, which may enable them to vocalize. To assess the potential for burbot to make calls, pre-spawning adult burbot were collected and placed in a large under-ice enclosure in Great Slave Lake, Northwest Territories, Canada, along with a recorder that monitored low frequency sound over their spawning period. The recorded acoustic data revealed that burbot called coincident with the onset of their spawning period and that the call signatures were stereotypical of swim bladder generated vocalizations made by other gadoid fishes. Burbot showed a wide repertoire of calls, from slow knocks to fast buzzing, similar to the closely related haddock (Melanogrammus aeglefinus). Although never-before documented, calling by fish under ice-cover is likely an important part of the mating system of under-ice spawning gadoids because light limitation would reduce the usefulness of visual cues. These under-ice communications may be affected by anthropogenic noise from increasing resource development in northern regions.

Diel vertical migration of adult burbot: a dynamic trade-off among feeding opportunity, predation avoidance, and bioenergetic gain

Diel vertical migration (DVM) of pelagic organisms is typically attributed to bioenergetic gain, foraging opportunity, predator avoidance, and multifactor hypotheses. While a number of benthic species perform nightly migrations into shallower waters, the function of these DVMs has largely been ignored in benthic fishes. We used depth and temperature sensing telemetry to investigate DVM function in burbot (Lota lota), a freshwater benthic piscivore. We modeled the influence of season, diel period, and body size on the depth, vertical activity, migration probability, and thermal experience of 47 adult burbot over 2 years in a reservoir in British Columbia, Canada. Burbot were found to occupy significantly shallower water at night than during the day. Our results, which showed elevated nightly activity and a seasonal size-structured depth distribution during DVMs, suggest these migrations likely provide a feeding opportunity “window” for this nocturnal predator, constrained by predation or cannibalism threats to smaller individuals. The observed thermal experience patterns suggest DVM may also provide a seasonal bioenergetic advantage. Our detection of within-individual plasticity in migration strategy is indicative of a partial migration. Taken together, our results suggest a multifactor DVM hypothesis: a dynamic trade-off among bioenergetic advantage, foraging opportunity, and predation threat.

Temporal Changes and Sexual Differences in Spatial Distribution of Burbot in Lake Erie

AbstractWe used GIS mapping techniques to examine capture data for Burbot Lota lota from annual gill‐net surveys in Canadian waters of Lake Erie during late August and September 1994–2011. Adult males were captured over a larger area (3–17% for ≥20% maximum yearly catch [MYC]) than adult females. More males than females were caught in the gill nets in 14 of the 15 study years. Collectively, these results support a hypothesis of greater activity by adult males during summer, when Burbot are actively feeding. The area of capture contracted by more than 60% (for ≥20% MYC) for both sexes during the time period, which is consistent with the documented decrease of the Burbot population in the lake. The sex ratio (females: males) varied over the time series but declined steadily from 0.97 in 2001 to 0.59 in 2011. The overlap in the capture areas of adult males and females was scale dependent. The depth distribution at which adult Burbot were caught did not change over the time series, and there was no difference in the median depths (about 30 m) at which adult male and female Burbot were caught. The last results are consistent with the Burbot's reliance on coldwater habitats. Additional research is recommended, including telemetry to describe daily and seasonal movements and assessment of gender bias in active and passive capture gear.

Burbot Early Life History Strategies in the Great Lakes

AbstractBurbot Lota lota exhibit four previously known reproductive strategies in the Great Lakes region. In this paper we review those strategies and provide evidence for a fifth one—delayed deepwater spawning. The four known, shallow‐water strategies are as follows: (1) spawning by self‐sustaining, landlocked populations, (2) spawning in tributaries in winter and the exit of larvae to a Great Lake, (3) spawning by residents in a spawning stream with access to a Great Lake, and (4) spawning on unconsolidated and rocky areas in shallow water in winter in the lake proper. Resident, landlocked populations exist in some Michigan and Wisconsin rivers (e.g., the Muskegon River in Michigan). The evidence for winter tributary spawning is the appearance of newly hatched Burbot in the St. Marys and Bark rivers during April–June. Evidence for Burbot juveniles leaving spawning streams is U.S. Fish and Wildlife Service tributory mouth trap data. The evidence for winter nearshore spawning comes from power plant monthly entrainment studies (Mansfield et al. 1983). Our proposed fifth strategy is spring and summer spawning at deep reefs, where there is probably cobble or boulder habitat. Our evidence comes from midlake reefs in Lake Michigan and offshore areas of Lake Huron: (1) we collected adult Burbot at midlake reefs in Lake Michigan, (2) we collected many Burbot larvae (many of which were newly hatched) from Lakes Michigan and Huron in June–August, and (3) we collected a Burbot egg in a PONAR grab in mid‐July from 73 m in southern Lake Huron. An important question remains, namely, which life history strategy provides the highest recruitment success for this species. It may be that adaptability ensures the survival of this important, top‐predator fish during periods of crisis (e.g., encounters with dams, Sea Lamprey Petromyzon marinus predation).

Ups and Downs of Burbot and Their Predator Lake Trout in Lake Superior, 1953–2011

AbstractThe fish community of Lake Superior has undergone a spectacular cycle of decline and recovery over the past 60 years. A combination of Sea Lamprey Petromyzon marinus depredation and commercial overfishing resulted in severe declines in Lake Trout Salvelinus namaycush, which served as the primary top predator of the community. Burbot Lota lota populations also declined as a result of Sea Lamprey depredation, largely owing to the loss of adult fish. After Sea Lamprey control measures were instituted in the early 1960s, Burbot populations rebounded rapidly but Lake Trout populations recovered more slowly and recovery was not fully evident until the mid‐1980s. As Lake Trout populations recovered, Burbot populations began to decline, and predation on small Burbot was identified as the most likely cause. By 2000, Burbot densities had dropped below their nadir in the early 1960s and have continued to decline, with the densities of juveniles and small adults falling below that of large adults. Although Burbot populations are at record lows in Lake Superior, the density of large reproductive adults remains stable and a large reserve of adult Burbot is present in deep offshore waters. The combination of the Burbot's early maturation, long life span, and high fecundity provides the species with the resiliency to remain a viable member of the Lake Superior fish community into the foreseeable future.

Variability in Burbot Cohort Abundance at Juvenile and Adult Stages in Columbia Lake, British Columbia

AbstractThis study examined changes in the abundance of juvenile (age‐0 and age‐1) and adult Burbot Lota lota in Columbia Lake, British Columbia, for the 1991–1999 cohorts. The objectives were to quantify the degree of variation in cohort abundance at different life stages and investigate the timing of recruitment limitation. Adult spawner abundance and age composition were monitored at a tributary spawning site from 1996 to 2001. Juvenile cohort abundance was estimated from 1997 to 1999, providing age‐0 abundance indices for the 1997–1999 cohorts and age‐1 indices for the 1996–1998 cohorts. The number of tributary spawners declined from about 1,500 in 1996 and 1997 to 86 in 1999 and then rebounded to 995 by 2001. Adult length frequency and age composition showed that this fluctuation reflected periodic influxes of strong cohorts that dominated the spawning population. The strongest new cohort (1999) observed at the tributary in 2001 came from the smallest number of tributary spawners. Substantial differences in the juvenile abundance of cohorts spawned from similar numbers of adults (1996, 1997) suggested a density‐independent effect at the egg or larval stage. The 1999 cohort, however, was more abundant than several other cohorts at the adult stage but not at age 0, suggesting a second limiting period after the first growing season. Possible explanations for the exceptional survival of the 1999 cohort include a temporary expansion of interstitial habitat caused by unusually high water levels and low abundance of older Burbot. As large fluctuations in cohort abundance appear to be characteristic of some Burbot populations, inclusion of age composition is recommended for population assessments.

A spatial analytical approach for selecting reintroduction sites for burbot in English rivers

1.?Availability of suitable habitat is a prerequisite for species reintroduction success, and to ensure population persistence, investigations of a species’ habitat utilisation throughout its life history should be conducted as part of a feasibility study. 2.?Habitat utilisation models for burbot, Lota lota, developed using data from field studies conducted in France and Germany and information from the literature were used to assess the feasibility of reintroducing burbot into rivers of its former native range in eastern England. 3.?Per cent tree roots, aquatic vegetation and flow types were important predictors of adult burbot abundance. Furthermore, the habitat utilisation models were supplemented with information from the literature, which suggested that off-channel habitat such as wetlands and backwaters is important for spawning and nursery stages. 4.?An assessment of the habitat availability in the rivers of the burbot’s former native range using variables related to spawning and nursery and adult life stages showed that although adult habitat was widely distributed, the availability of spawning and nursery habitat was less abundant, potentially limiting successful reestablishment. 5. ?Potential suitable habitat was concentrated in the central and southern areas of the species’ former English distribution. Overall, rivers of the burbot’s former range potentially afford suitable habitat to sustain a reintroduced population. However, sites should be preferentially selected on the basis of having appropriate spawning and nursery areas

Evaluation of methods for the collection and fertilization of burbot eggs from a wild stock for conservation aquaculture operations

Summary In the Kootenay River, British Columbia, Canada, burbot (Lota lota maculosa) numbers have diminished to near extirpation due to factors including physical changes to habitat and overfishing. Habitat restoration is currently underway but short-term recovery measures include the release of hatchery-reared burbot. Moyie Lake has been identified as a suitable brood source for a conservation aquaculture program but uncertainties remain regarding current population size, the feasibility of capturing broodstock and the ability to collect eggs from wild spawners. Specific objectives of our study were to: (i) develop a length at age key to provide a non-destructive means of population age structure identification, (ii) determine the location and general habitat characteristics of burbot spawning locations on Moyie Lake, (iii) provide a marked sample for future population estimation, and (iv) investigate the feasibility of collecting gametes for use in a conservation aquaculture program. A total of 181, 554, and 370 burbot were captured in 2009, 2010 and 2011, respectively. No significant relationship was established between length and age for burbot on Moyie Lake. Spawning burbot were observed over a number of different habitats, but high use areas consisted of steep banks dominated by a mix of gravel/boulder/cobble substrates. Mature burbot were reliably collected each year, and eggs from females were fertilized and transported to the hatchery. Egg survival was highly variable (range 0–98%) and resulted in an estimated 353 429, 3 032 143, and 3 970 283 eggs for use in the aquaculture program in 2009, 2010 and 2011, respectively. Results of this study demonstrate that gametes can be collected from adult burbot during spawning and eggs can be successfully fertilized in the field. Further methodological refinement aimed at improving egg fertilization and subsequent survival to the hatchery will be important as recovery moves forward.

Husbandry conditions in burbot ( Lota lota L.): Impact of shelter availability and stocking density on growth and behaviour

The nocturnal and benthic burbot ( Lota lota L.) could be a new fish species for freshwater aquaculture. However there are no trials studying growth of juvenile and adult fish. In this study the impact of the husbandry conditions shelter availability and stocking density on growth and behaviour was investigated. In experiment 1 juvenile burbot (119.8 g ± 19.5) were reared with different shelter availability (unsheltered, medium sheltered and high sheltered) in partly covered tanks for 12 weeks and were fed overnight (10 h). In experiment 2 adult burbot (361.8 g ± 58.2) were reared at different stocking densities (2.4, 4.9 and 9.7 kg m − 2 ) in completely covered tanks for 16 weeks and were fed during first two night hours. Swimming activity and feeding behaviour were studied in both experiments using a video-based infrared illuminated system which started with the last day time hour and ended with the second day time hour. Different shelter availability had no effect on burbot growth (SGR: 0.65, 0.69 and 0.70% day − 1 ), but it did significantly affect shelter use, swimming activity and feeding behaviour. Fish of the high sheltered group showed higher shelter use, lower swimming activity and lower feeding activity. Burbot of all treatments showed a distinct feeding activity during the first three night hours (30.2% ± 12.3 for high sheltered and 44.0% ± 9.8 for unsheltered). In experiment 2 growth (SGR: 0.40, 0.41 and 0.42% day − 1 ) of adult burbot was not affected by stocking density meaning culturing of burbot is possible up to a density of 18 kg m − 2 without negative effects on growth and size heterogeneity. Swimming activity in the low density group was significantly lower during dawn and the first day time hour than in the other two groups. Feeding activity was significantly higher in the medium and high density group than in the low density group. This study provides a basis for further development of burbot aquaculture.

Evidence for predatory control of the invasive round goby

We coupled bioenergetics modeling with bottom trawl survey results to evaluate the capacity of piscivorous fish in eastern Lake Erie to exert predatory control of the invading population of round goby Neogobius melanostomus. In the offshore (>20 m deep) waters of eastern Lake Erie, burbot Lota lota is a native top predator, feeding on a suite of prey fishes. The round goby invaded eastern Lake Erie during the late 1990s, and round goby population size increased dramatically during 1999–2004. According to annual bottom trawl survey results, round goby abundance in offshore waters peaked in 2004, but then declined during 2004–2008. Coincidentally, round goby became an important component of burbot diet beginning in 2003. Using bottom trawling and gill netting, we estimated adult burbot abundance and age structure in eastern Lake Erie during 2007. Diet composition and energy density of eastern Lake Erie burbot were also determined during 2007. This information, along with estimates of burbot growth, burbot mortality, burbot water temperature regime, and energy densities of prey fish from the literature, were incorporated into a bioenergetics model application to estimate annual consumption of round goby by the adult burbot population. Results indicated that the adult burbot population in eastern Lake Erie annually consumed 1,361 metric tons of round goby. Based on the results of bottom trawling, we estimated the biomass of yearling and older round goby in offshore waters eastern Lake Erie during 2007–2008 to be 2,232 metric tons. Thus, the adult burbot population was feeding on round goby at an annual rate equal to 61% of the estimated round goby standing stock. We concluded that the burbot population had high potential to exert predatory control on round goby in offshore waters of eastern Lake Erie.

Interactions between native juvenile burbot (Lota lota) and the invasive spinycheek crayfish (Orconectes limosus) in a large European lake

Freshwater crayfish are successful invaders in many ecosystems and as cryptic nocturnal species display a potential niche overlap with benthic nocturnal fish. In this study, we tested the effects of the invasive spinycheek crayfish ( Orconectes limosus ) on native young-of-the-year (YOY) and adult burbot ( Lota lota ) in Lake Constance. Using mesocosm experiments, we tested if shelter preferences of YOY and adult burbot and crayfish changed between single and mixed species treatments. To further study the role of crayfish as a stressor for burbot, we monitored the nocturnal behaviour of the species in mesocosms using passive integrated transponder (PIT) tag technology and subsequently determined the plasma cortisol levels in burbot after single and mixed species treatments. Spinycheek crayfish successfully repelled YOY burbot from their preferred daytime shelters into alternative, previously unselected shelters. Crayfish also affected the nocturnal behaviour of YOY burbot by eliciting avoidance behaviour and caused an increase in the plasma cortisol levels. While adult burbot did not display any changes between single and mixed species treatments, our results indicate negative effects of spinycheek crayfish on YOY burbot. We conclude that the frequently dense, invasive crayfish populations in lakes may negatively influence local benthic fish populations via their YOY cohorts.

Effects of regulated discharge on burbot migration

Burbot Lota lota movement and river discharge were studied in the Kootenai River, Idaho, U.S.A. and British Columbia, Canada, downstream of Libby Dam, Montana, U.S.A. A total of 24 adult burbot with transmitters were tracked from 1994 to 2000, for analysis of a travel distance of ≥5 km in ≤10 days termed ‘stepwise movement’. Of 44 ‘stepwise movements’, significantly greater movements during pre‐spawning and spawning were observed when average daily discharges from Libby Dam were <300 m3 s−1, with a mean of 176 m3 s−1, similar to pre‐dam conditions. Burbot travelled at a greater rate during all seasons (3·36 km day−1) at discharges >300 m3 s−1(mean = 1·84 km day−1) than at discharges >300 m3 s−1 but no difference was found for the pre‐spawning and spawning period. Burbot that started ‘stepwise movements’ in low discharge conditions frequently stopped during low discharges.

Development and validation of a bioenergetics model for juvenile and adult burbot

Oxygen consumption of juvenile and adult burbot Lota lota was measured in an intermittent‐flow respirometer to determine the effect of temperature and fish body mass on metabolic rate. These results were combined with data from earlier experiments and the ‘Wisconsin bioenergetics’ model was constructed. The model was validated under laboratory conditions by comparing observed and predicted food consumption and growth of burbot fed on dead vendace Coregonus albula. There was a good correspondence between observed and estimated growth and food consumption under experimental conditions: the mean absolute per cent errors of growth and food consumption were 4·8 and 24·0%. Estimated values with the new model were an improvement over the Atlantic cod Gadus morhua model previously used for burbot. In the field, the reliability of food consumption estimates was verified by using polychlorinated biphenyls (PCB) accumulation as an indirect indicator of the food consumption rate. The total PCB concentration of nine out of 13 burbot was estimated accurately. Thus, the burbot model produced good estimates of food consumption, even under field conditions.

Parasites of Burbot, Lota lota, from Lake Huron, Michigan, U.S.A., with a Checklist of the North American Parasites of Burbot

Abstract Forty-five adult burbot, Lota lota, collected in July 1998 from Six Fathom Bank (Six Fathom Bank Lake Trout Refuge) and Yankee Reef in Lake Huron, Michigan, U.S.A., were examined for parasites. A total of 10 parasite species infected burbot. Diplostomum sp., Eubothrium rugosum, Haplonema hamulatum, Echinorhynchus salmonis, and Trichodina sp. infected 60% or more of the burbot examined from each location. Diplostomum sp. had the highest mean intensity, and E. salmonis had the highest mean abundance in burbot from Six Fathom Bank. Echinorhynchus salmonis had the highest mean intensity and mean abundance in burbot from Yankee Reef. Diplostomum sp., H. hamulatun, and E. salmonis in burbot from Yankee Reef had significantly higher mean intensities and mean abundances than those in fish from Six Fathom Bank. The lengths and weights of burbot from Yankee Reef were significantly greater than those of fish from Six Fathom Bank. A checklist of parasites of burbot from published records in North America is ...

Oxygen consumption of burbot, Lota lota(L.), fed different rations of vendace, Coregonus albula L.

Summary The oxygen consumption of adult burbot, Lota lota (L.), was examined to determine the effects of fasting and meal ration on oxygen consumption rates. The temperature (2.1 °C) was selected to represent ambient conditions for burbot in winter. The average pre-feeding oxygen consumption rate was 29.5 mg kg−1 h−1. Feeding affected the oxygen consumption rates since the apparent heat increment correlated significantly with the meal ration. However, the meal ration (i.e. vendace, Coregonus albula L.) did not affect the proportion of the ingested meal energy used in the apparent heat increment. When the meal ration was increased, peak oxygen consumption ranged from 1.2 to 2.2 times higher than the fasting level. Observed low oxygen consumption values suggest that the metabolic processes of burbot are strongly reduced in low temperatures.