Inhibitory effect of osmotic concentration, potassium and pH on motility of the sperm of the North American burbot Lota lota maculosa

Seminal plasma factors maintaining North American (NA) burbot Lota lota maculosa sperm quiescent were examined. Sperm were diluted into buffered saline solutions of various compositions and motility assessed. After 1 h in these solutions at 10° C, aliquots of the suspension were diluted with tap water and motility again assessed. Dilution of sperm in an incubation solution containing Ca²⁺ in the absence of K⁺ initiated sperm motility resulting in low motility when sperm were subsequently diluted in tap water. Incubation solutions with osmolalities >200 mOsm kg⁻¹ and containing 12·5 mM K⁺ prevented the onset of sperm motility and were associated with maximal sperm motility upon dilution in tap water. Sperm maintained at lower osmolalities exhibited limited motility upon dilution in tap water indicating interdependence between K⁺ and osmolality in maintaining sperm quiescent in the presence of Ca²⁺. Sperm kept in incubation solution at pH values < c. 7·5 for 1 h demonstrated reduced motility when subsequently diluted in tap water. That motility of sperm was pH sensitive was further indicated by CO₂ inhibition of motility. Therefore, NA burbot sperm are probably maintained in an immotile state, yet with potential for motility, by combination of high K⁺, osmolality and possibly pH. The results from this study differ from published information on sperm quiescence in the temporally and geographically distinct Eurasian burbot Lota lota lota .     

Microsatellites from the burbot (Lota lota), a freshwater gadoid fish (Teleostei)

We developed 21 polymorphic dinucleotide microsatellite loci, (CA)_n and (CT)_n, for the Holarctic freshwater fish, Lota lota, using an enriched genomic library protocol. The species has an interesting life history because winter‐spawning adults migrate over long distances to form spawning aggregations, a behaviour which should maintain genetic homogeneity across large spatial scales. Availability of the reported microsatellites will facilitate the investigation of population genetic structure with regard to postglacial colonization history and conservation strategies. The primers were screened on 30 individuals from a natural population (Lake Constance, southern Germany), revealing three to 24 alleles per locus with expected heterozygosities ranging from 0.48 to 0.93.     

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.     

Effects of temperature and a piscivorous fish on diel winter behaviour of juvenile brown trout (Salmo trutta)

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Ontogenetic niche shifts and resource partitioning in a subarctic piscivore fish guild

The feeding ecology of three piscivorous fish species (perch (Perca fluviatilis), pike (Esox lucius) and burbot (Lota lota)), was studied in the subarctic Pasvik watercourse (69 °N), northern Norway and Russia. All three species primarily occupied the benthic habitats in the watercourse. Perch and burbot exhibited distinct ontogenetic niche shifts in food resource use, perch changing from a dominance of zooplankton to zoobenthos to fish, and burbot from zoobenthos to fish. Fish prey dominated the diet of all the investigated size-classes of pike, but small-sized pike (<20 cm) were not represented in the sample. Fish prey size was positively related to predator size in all three species. Whitefish (Coregonus lavaretus) was the dominant prey of pike and large-sized burbot and perch. Nine-spined sticklebacks (Pungitius pungitius) was also an important prey and appeared to be a dietary stepping-stone enhancing the transition from invertebrate feeding to consumption of large-sized whitefish prey for all three predators. A cluster analysis separated the different size groups of the three predator species into five functional feeding groups, most of them containing two or all three species. Within these feeding groups, and especially among the piscivorous size-classes, there was a strong and significant interspecific overlap in prey selection, and the dietary similarities between the species were in general much larger than the intraspecific similarities between ontogenetic stages. All three piscivorous species are important top predators in the aquatic food web of the watercourse, and their ontogenetic diet shifts and resource partitioning patterns generate a substantial food web complexity in this subarctic ecosystem.     

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.     

Distribution and onshore migration behaviour of burbot larvae in Lake Constance, Germany

Larval abundance of burbot Lota lota in the pelagic zone of Lake Constance, Germany, peaked during April and remained at a constant but lower level until mid‐June. From the end of May onwards a significant diel vertical migration pattern was observed: while burbot larvae were distributed above as well as below the thermocline in the daytime with the highest percentages of abundance at water depths of 30 and 50 m (below the thermocline) on 5 and 25 June, they were concentrated from 2 to 15 m (above the thermocline) during the night. This migration pattern coincided with a significant decline in the food items preferred by burbot at this life stage, cyclopoid copepods. This phase of diel vertical migration lasted for c . 4 weeks until the burbot larvae suddenly disappeared from the pelagic zone. This indicated a short phase, lasting only a few days, of larval settlement into profundal benthic habitats. This was supported by a significant, abrupt decrease in the absolute growth rates of the larvae at day 56 after hatching. The day–night pattern of vertical migration observed could be assumed to be a transition phase from a pelagic to a benthic lifestyle, as reported for juveniles of several other, marine gadoid species.     

Burbot (Lota lota) exhibit plasticity in life-history traits in a small drainage at the southwestern-most extent of the species' native range

Little is known about the life-history traits exhibited by burbot (Lota lota) throughout their circumpolar range. Monitoring burbot movements between lentic and lotic habits and collection of demographic data (length, age, sex, and maturity) were used to answer the following questions in the Torrey Creek drainage of west-central Wyoming, USA: (a) is there plasticity in the life-history traits of the burbot population, (b) do Trail Lake origin and Torrey Creek origin burbot interchange during the spawning period, and (c) is there a difference in growth and age at sexual maturity between burbot captured in Trail Lake and Torrey Creek? Results indicated that burbot in Trail Lake and Torrey Creek exhibit plasticity in their life history traits. Directional movement of PIT-tagged burbot in Trail Lake and Torrey Creek was monitored nearly continuously by tandem stream-width antennas. Thirty-five percent of lentic-origin burbot migrated upstream into Torrey Creek, and 11% of lotic-origin burbot migrated downstream of the antennas near the Torrey Creek inlet to Trail Lake. Migratory activity of burbot was highest during the late winter and early spring at a time that coincided with spawning. Additionally, Torrey Creek-origin burbot were smaller and younger than Trail Lake-origin burbot. In addition to documenting migration, the sampling of small, sexually mature burbot in Torrey Creek suggests that stream-resident burbot reach maturity earlier than adfluvial and lacustrine burbot in Trail Lake. Furthermore, high catch rates of age-0 burbot indicate that Torrey Creek upstream from Trail Lake provides nursery habitat to the burbot population. Life history trait plasticity and spawning and nursery habitats documented in this study should be considered when selecting conservation actions for this unique burbot population.     

The response of burbot (Lota lota) to change in lake trout (Salvelinus namaycush) abundance in Lake Opeongo,Ontario

The purpose of this study was to test the hypothesis that the burbot and lake trout compete with or prey on each other, and that a change in the abundance of lake trout has triggered a response in the burbot population. Burbot growth, length-weight relationship and population size did not change, and it appears that at these population levels, the changes in lake trout abundance had no detectable effect on burbot. It is suggested that the burbot population in Lake Opeongo is limited at the larval stage by competition with, or predation by, a planktivore, the lake herring.     

Food,growth, habitat,and community interactions of young-of-the-year burbot,Lota lota L., in a Precambrian Shield lake

The burbot, Lota lota, is a widely distributed gadid of the northern circumpolar regions of North America and Eurasia. Despite its near ubiquity over much of its range, relatively little is known about its biology during the first year of life.Burbot sac-fry of 3 mm total length, hatched under the ice in early May in Shebandowan Lake. Their first foods following atrophy of the yolk-sac were copepods and cladocerans which they captured pelagically. At first the fry swam in small schools, high in the water column of the near-shore littoral, and fed during the daytime. Upon reaching 30 mm in total length, the burbot fingerlings became solitary and benthic, and fed primarily at night, almost exclusively on the amphipod, Hyalella azteca. Amphipods constituted about 75 per cent by number of all the food consumed by burbot fingerlings in their first year of life. Growth was rapid from May to the end of July, tapered off during August to October, and effectively stopped by November at freeze-up. The principal habitat of burbot fingerlings during the benthic stages of their life was the near-shore littoral, in depths ranging from 0.5 m to 4.0 m. There, they were sheltered by boulder shoals, sunken trees or other debris, or beds of quillworts (Isoetes sp.). The principal ichthyofauna that cohabited with the burbot included the sculpin (Cottus cognatus), the smallmouth bass (Micropterus dolomieui), two etheostomatines (Etheostoma nigrum) and (E. exile) and the yellow perch (Perca flavescens). Burbot fingerlings were subjected to low levels of predation from the nocturnal foraging of walleyes (Stizostedion vitreum).