Seasonal dynamics of fatty acid composition in female northern pike (Esox lucius L.)

Seasonal changes in the fatty acid composition of neutral and polar lipids were measured in the ovary, liver, white muscle, and adipopancreatic tissue of northern pike. The role of environmental and physiological factors underlying these changes was evaluated. From late summer (August–September) to winter (January–March), the weight percentage of n-3 polyunsaturated fatty acids (especially 22:6n3) declined significantly in the neutral lipids of all somatic tissues examined. However, large quantities of n-3 polyunsaturated fatty acids accumulated in the recrude cing ovaries during fall and the weight percentage of n-3 polyunsaturated fatty acids in ovary polar lipids also increased significantly. Additionally, the n-3 polyunsaturated fatty acid content of somatic polar lipids increased significantly during fall due to increases in the total polar lipid content of the somatic tissues. This suggests that during fall n-3 polyunsaturated fatty acid are diverted away from somatic neutral lipids and thereby conserved for use in ovary construction and for incorporation into tissue polar lipids. The percentage of n-3 polyunsaturated fatty acid in ovary neutral lipids also declined during fall and early winter, perhaps as an adaptation to conserve these fatty acids for storage in oocyte polar lipids and later incorporation into cellular membranes of the developing embryo. Reductions in the n-3 polyunsaturated fatty acids content of somatic and ovarian neutral lipids during fall were compensated for specifically by increases in the percentage of monounsaturated fatty acids rather than saturated fatty acids. This suggests that the ratio of saturated to unsaturated fatty acids in pike neutral lipid, is regulated physiologically, and hence may influence the physiological functioning of these lipids. During fall and early winter the percentage of saturated fatty acids declined significantly in the polar lipids of all tissues examined. This change was consistent with the known effects of cold acclimation on the fatty acid composition of cellular membranes. As the ovaries were recrudescing from September to January, liver polar lipids exhibited significant decreases in the percentage of total polyunsaturated fatty acids and n-3 polyunsaturated fatty acids and increases in monounsaturated fatty acids, and acquired a fatty acid composition very similar to that of ovary polar lipids. Therefore, seasonal changes in the percentage of polyunsaturated and monounsaturated fatty acids in liver polar lipids probably reflect the liver's role in vitellogenesis rather than the effects of temperature on membrane fatty acid composition. At all times of year, the fatty acid compositions of white muscle and adipopancreatic tissue neutral lipids were very similar, which may indicate a close metabolic relationship between these lipid compartments.Abbreviations AP adipopancreatic - BHT butylated hydroxytoluene - CI confidence interval - EFA essential fatty acids - MUFA monounsaturated fatty acids - NL neutral lipids - PL polar lipids - PUFA polyunsaturated fatty acids - SFA saturated fatty acids     

A comparison of slimy sculpin (Cottus cognatus) populations in arctic lakes with and without piscivorous predators

Arctic slimy sculpin were sampled by passive trapping in lakes containing the predators lake trout and burbot (LT lakes), and lakes lacking sculpin predators (NoLT lakes). Sculpin food abundance (chironomid biomass) from the rocky littoral zone was compared with that from the deep water sediment zone. Distribution, size, growth, age, condition and relative abundance of sculpin were examined. Spatial distribution of sculpin was different between lake types, with more and larger sculpin found over the sediment zone in NoLT lakes. There were no seasonal patterns evident in this distribution and catch per unit effort was not significantly different between LT and NoLT lakes. Biomass of chironomids, the major food of the sculpin, was higher in the sediments than on the rocks, suggesting that sediments should be the preferred environment in the absence of piscivores. Longevity of sculpins varied between IV and VIII years and was not correlated with lake type. Sculpin size frequency distributions were shifted toward slightly larger fish in NoLT lakes. Sculpin growth curves and condition estimates did not reveal a difference between lake types, but comparison of mean ototlith interannular distances between lake types showed a trend, significant in year 4, toward more growth in no lake trout lakes. These results suggest that the presence of piscivores is an important factor limiting arctic slimy sculpin distribution and may act in concert with food supply to impact sculpin growth.     

Influences of slimy sculpin (Cottus cognatus) predation on the rocky littoral invertebrate community in an arctic lake

We tested the role of the slimy sculpin (Cottus cognatus), a benthic fish, in structuring the rocky littoral invertebrate community in Toolik Lake, Alaska. Comparisons of sculpin gut contents and prey community structure indicated that these fish forage selectively, eating proportionally more large and motile prey, and proportionally fewer small and sessile forms. Field experiments compared the effects of natural, reduced and elevated sculpin densities on benthic community structure. At natural levels of sculpin density, biomass of trichopteran larvae were reduced by more than 50%, and predatory chironomid larvae by 27%, in comparison to areas where sculpin were excluded. Tube-dwelling and small free living chironomid larvae were unaffected at normal sculpin densities. Under artificially high sculpin densities, there was some reduction of tube-dwelling chironomids, but the small free living ones remained unaffected. There appears to be a threshold length of about 3.5 mm, below which chironomid larvae are free form sculpin predation. Tube-dwelling chironomids may be longer than this threshold, but still avoid predation by having most of their body hidden in their tubes.     

Seasonal changes in condition indices in adult mature and non-maturing burbot, Lota lota (L.), in the north-eastern Bothnian Bay, northern Finland

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north-eastern Bothnian Bay are described. The significance of the so-called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index ( K ₂), liver index ( K ₁), intestine index ( K ₁) and gonad index ( K_g ) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non-maturing but were 40 cm or more in length. K ₂, K ₁ and K ₁ were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non-maturing burbot were never in poorer condition than mature ones. As mature and non-maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.     

Genetic admixture of burbot (Teleostei: Lota lota) in Lake Constance from two European glacial refugia

The burbot, Lota lota, is the only freshwater species of the codfish family and has a Holarctic distribution. Pleistocene glaciations caused significant geographical differentiation in the past, but its life history characterized by winter spawning migrations over large distances is likely to homogenize populations by contemporary gene flow. We investigated the population genetic structure of 541 burbots from Lake Constance and adjacent Rhine and Danube tributaries in Europe using the entire mitochondrial DNA (mtDNA) control region and 11 microsatellites. Microsatellites revealed considerable population divergence (F(ST) = 0.26) and evidenced recent bottlenecks in two Central European rivers. In accordance to previous evidence two main phylogeographic lineages (Atlantic and Danubian) were found co-occurring at similar frequencies in Lake Constance, where they currently undergo random mating as indicated by microsatellites. The Danubian lineage contributed only a small proportion to the lake's mtDNA diversity, and probably expanded within the lake shortly after its formation approximately 10,000-15,000 BP. The larger Atlantic haplotype diversity suggested a population expansion older than the lake itself. Levels of admixture at microsatellite loci were less obvious due to their high variability, and coalescence methods were used to estimate past admixture proportions. Our results reinforce a model of a two-step colonization of Europe by burbot from an ancestral Danubian refuge, and confirm the persistence of a secondary Atlantic refuge, as proposed to exist for other freshwater fish. We conclude that the present-day burbot population in Lake Constance bears the genetic signature of both contemporary gene flow and historical separation events.     

Production,consumption and prey availability of northern pike (Esox lucius), pikeperch (Stizostedion lucioperca) and European catfish (Silurus glanis): a bioenergetics approach

Bioenergetics models were applied for the assessment of food consumption of northern pike, pikeperch and European catfish in drainable ponds of 0.4 ha. The ponds were stocked with known numbers of the 0⁺ predators. The prey fish consisted of naturally recruited 0⁺ cyprinids (rudd, roach and bream). The study shows that the impact of the three 0⁺ piscivores on the aquatic system differs, which is related to the feeding behaviour and habitat use of the fish. All piscivores realised part of their production on a non-fish diet.     

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.     

Individual specialization and trophic adaptability of northern pike (Esox lucius): an isotope and dietary analysis

Northern pike (Esox lucius) are often considered to be specialist piscivores, but under some circumstances will continue to eat invertebrates as adults. To examine effects of fish assemblage composition on the trophic ecology of pike, we combined stable isotope analysis (SIA) of carbon and nitrogen and stomach content analysis (SCA) on pike from five lakes in northern Alberta, three of which contain only pike (“pike-only”) and two that also contain yellow perch (Perca flavescens) or white sucker (Catostomus commersoni) (“pike-other”). Fish were more important as prey and empty stomachs, which often characterize piscivores, were significantly more frequent in pike-other than in pike-only lakes. However, even though invertebrates were more important for pike in pike-only lakes, SIA and SCA indicated that invertebrates were also an important component of pike diets in pike-other lakes. SIA and SCA also revealed considerable intrapopulation variation in trophic ecology, with individuals in some populations differing by as much as two trophic levels. Comparisons of stomach contents and isotope signatures of the same fish suggested that within these variable populations, specialization on invertebrates or fish was a long-term trait of some individuals. SIA indicated that trophic position increased and diets shifted to a greater importance of littoral prey as pike grew in pike-only lakes, but not in lakes with other fish present. Trophic adaptability in northern pike is expressed at both the population level, where the trophic ecology is sensitive to differences in prey regimes, and at the organismal level, in the form of intrapopulation variation and individual specialization. Received: 1 July 1998 / Accepted: 3 February 1999     

Changes in elemental composition of fertilized and unfertilized northern pike (Esox lucius) eggs incubated in buffer with and without dimethyl sulfoxide: An X-ray microanalysis study

Fertilized and unfertilized eggs from the northern pike (Esox lucius) were incubated 2 hr in buffer with 0 and 10% (v/v) dimethyl sulfoxide and then quickly frozen in the wells of aluminum blocks submerged in liquid nitrogen. Control eggs and ovarian fluid were similarly frozen immediately after collection. The frozen eggs were sectioned, freeze dried, mounted on stubs, and carbon coated. X-ray microanalysis was used to determine changes in element levels and dimethyl sulfoxide (Me₂SO) penetration in the zona radiata, cytoplasm, cortical alveoli, and egg yolk. Unfertilized eggs incubated without Me₂SO showed decreased levels of Na, Cl, and K in the zona radiata; fertilized eggs, incubated without Me₂SO showed decreased levels of Na, P, and Cl in the zona radiata and increased levels of K in the cytoplasm; unfertilized eggs, incubated with 10% Me₂SO showed decreased Na and Cl in the zona radiata, decreased K in the cytoplasm and increased K in the cortical alveoli; fertilized eggs incubated in buffer with 10% Me₂SO showed decreased levels of Na, P, Cl, and K (zona radiata), P, Cl, and K (cytoplasm), Na (yolk), and increased Cl in the yolk (all P<.01). Me₂SO (v/v) levels reached 1.5-3.1% in the zona radiata, 0-3.2% in cytoplasm, 2.3-8.7% in cortical alveoli, and 0-1.6% in the yolk. Unfertilized eggs showed more Me₂SO penetration than fertilized eggs.     

Mechanosensory based orienting behaviors in fluvial and lacustrine populations of mottled sculpin (Cottus bairdi)

We compared prey-orienting and rheotactic behaviors in a fluvial (Coweeta Creek) and lacustrine (Lake Michigan) population of mottled sculpin. Blinded sculpin from both populations exhibited unconditioned, mechanosensory based rheotaxis to low velocity flows. Whereas Lake Michigan sculpin generally showed increasing levels of positive rheotaxis to increasing velocities, Coweeta Creek sculpin show varying levels of positive rheotaxis at low to intermediate velocities and often reduced positive rheotaxis or even negative rheotaxis at the highest velocities (12 cm s^-1). Blinded Lake Michigan, but not Coweeta Creek mottled sculpin exhibited an orienting response to a small (3 mm diameter) artificial prey (50 Hz vibrating sphere). In conclusion, the two populations differed in the strength and polarity of the rheotactic response at higher velocities and in their responsiveness to mechanosensory cues from epibenthic prey sources. These behavioral differences have most likely arisen from different learning experiences in different habitats and from the greater importance of visual cues to the Coweeta Creek mottled sculpin and mechanosensory cues to Lake Michigan mottled sculpin in the sensory guidance of orienting behaviors.     

Mechanosensory based orienting behaviors in fluvial and lacustrine populations of mottled sculpin ( Cottus bairdi )

We compared prey-orienting and rheotactic behaviors in a fluvial (Coweeta Creek) and lacustrine (Lake Michigan) population of mottled sculpin. Blinded sculpin from both populations exhibited unconditioned, mechanosensory based rheotaxis to low velocity flows. Whereas Lake Michigan sculpin generally showed increasing levels of positive rheotaxis to increasing velocities, Coweeta Creek sculpin show varying levels of positive rheotaxis at low to intermediate velocities and often reduced positive rheotaxis or even negative rheotaxis at the highest velocities (12?cm?s^?1). Blinded Lake Michigan, but not Coweeta Creek mottled sculpin exhibited an orienting response to a small (3?mm diameter) artificial prey (50?Hz vibrating sphere). In conclusion, the two populations differed in the strength and polarity of the rheotactic response at higher velocities and in their responsiveness to mechanosensory cues from epibenthic prey sources. These behavioral differences have most likely arisen from different learning experiences in different habitats and from the greater importance of visual cues to the Coweeta Creek mottled sculpin and mechanosensory cues to Lake Michigan mottled sculpin in the sensory guidance of orienting behaviors.     

Seasonal changes in some blood chemistry parameters and in relative liver and gonad weights of pike (Esox lucius L.) from the River Danube

Samples from a natural population of pike (Esox lucius L.) from the River Danube were used in a 12-month study to determine seasonal variations in biochemical parameters of pike blood sera, hepatosomatic index (HSI) and gonadosomatic index (GSI). The ranges of enzyme activities for sample means were: aspartate aminotransferase (ASAT) 252.0–583.8 U 1⁻¹, alanine aminotransferase (ALAT) 4.9–11 -2 U1 and alkaline phosphatase (AP) 39.5–91.8 U1⁻¹. The ranges of other parameters analysed in serum were total protein 27.7–40.1 g 1 ¹, urea 0.57–l.52 mmol 1 ¹ and creatinine 21.2–118.6 μmol 1 ¹. The range of sample means for HSI and GSI were 1.28–4.16 and 0.07–20.2 respectively. Temperature ranged from 4.5 to 23.5°C. The activity of serum AP was positively correlated to water temperature in males only, while urea and creatinine showed a positive correlation to water temperature in individuals of both sexes. GSI was correlated significantly with HSI in females. Total protein reached the lowest values during the spawning period, while creatinine levels depended on both the sex and season.     

Life-history variations in the fluvial sculpin, Cottus nozawae (Cottidae), along the course of a small mountain stream

Life-history variations in male and female fluvial sculpins, Cottus nozawae, were studied in a small mountain stream in Hokkaido, Japan, primarily by using capture-mark-recapture methods. At three study areas established along the stream course, the majority of marked sculpins were recaptured in their original location over one or more years, indicating their long-term occupation of each restricted habitat area. Sculpin densities increased toward the upstream habitats, whereas individual growth rates were more rapid downstream. In both sexes, sculpins distributed downstream matured at a larger body size and later in life than upstream sculpins, clearly demonstrating a clinal variation in these respects. A comparison of life-history variations in C. nozawae with those in amphidromous C. hangiongensis suggests that intrapopulational life-history variations in the former might be environmentally induced, and that one of the most important determinants for the variations in Cottus species might be population density.     

A survey of the spawning of perch (Perca fluviatilis), pike (Esox lucius), and roach (Rutilus rutilus), using artificial spawning substrates in lakes

The development of spawning in perch, pike and roach in Lake Geneva has been studied by means of artificial spawning substrates, laid at different depths, from 1984 to 1993. In Lake Geneva, perch spawned in May. A rise of surface water temperature up to 14 °C stimulated spawning activity while bad weather (surface temperature at 10 °C) induced a spread of the spawning period over more than one month. The spawning period was delayed in years when the mean width of perch egg-ribbons was the largest; this corresponded to the biggest females. At the beginning of the spawning period (early in May), perch preferentially chose a depth of 4 m to spawn. In contrast, at the end of the spawning period, maximum spawning intensity was observed at a depth of 12 m. This phenomenon was more pronounced when water temperature rose above 14 °C in the top 4 m while it remained below 12 °C at a depth of 12 m. Pike spawned at the end of April and at the beginning of May in Lake Geneva. They preferred spruce branches among the different spawning substrates that we tested in Lake Vouglans. When the water temperature increased at the surface of Lake Geneva, pike preferred to lay their eggs on substrates set at 3 m depth where the temperature was cooler than in the surface layer (10.5 °C vs 14 °C). Roach spawned during the last two weeks of May or during the first two weeks of June in Lake Geneva, depending on water temperature. Spawning had generally been spread over a week, but a sudden decrease of water temperature could slow spawning intensity. Roach were able to lay their eggs on natural or synthetic substrates, located 0.5 m below the surface near the shore as well as, at a distance of several hundred metres from the shore. The survival of eggs was always above 90% for perch and roach and generally above 70% for pike.     

Pineal-retinal relationships: rhythmic biosynthesis and immunocytochemical localization of melatonin in the retina of the pike (Esox lucius)

Summary The levels of melatonin and the activities of two enzymes of the melatonin biosynthetic pathway, serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT), were measured throughout the light-dark cycle in the retina of a teleost fish, the pike. HIOMT activity did not display significant variations, whereas NAT activity and melatonin content showed a daily rhythm, high levels occurring during the night. The profiles of the latter two rhythms did not closely match one another and differed from those previously described in the pineal organ of the same species. These results are discussed with respect to a possible paracrine role of retinal melatonin. Melatonin-like immunoreactivity was found in the photoreceptor cell layer and in the Müller cells of the inner nuclear layer. The intensity of the melatonin-like immunoreactivity varied throughout the 24 h light-dark cycle, in good correlation with the variations in the melatonin level as measured by radioimmunoassay.This article is dedicated to the memory of Dr. Klaus Hoffmann     

Ultrastructure of atrial and ventricular myocardium in the pike Esox lucius L. and mackerel Scomber scombrus L. (Pisces)

Summary Atrial and ventricular muscle in the pike and mackerel hearts consists of narrow, branching cells. The atrial cells in the two species are similar whereas the ventricular cells differ. The sarcolemma is attached to the Z and M lines of the sarcomere. Intercalated discs are common, and the transverse parts display desmosomes and intermediate junctions. Nexuses are uncommon and only occur in the longitudinal parts of the intercalated discs. The sarcoplasmic reticulum forms a regular hexagonal network on the myofibrillar surface. Subsarcolemmal cisternae form peripheral couplings at the I-A level. Junctional processes are usually inconspicuous, but an electron dense substance is present between the sarcolemma and the Junctional sarcoplasmic reticulum. Specific heart granules are common in atrial cells of both species and in ventricular cells of the pike, but are very scarce in mackerel ventricular muscle.This work was supported by grants from the Norwegian Research Council for Sciences and the Humanities     

Accumulation of fluorescent age pigments in embryos and larvae of pike,Esox lucius (Esocidae,Teleostei) at different incubation temperatures

Synopsis Accumulation of fluorescent age pigments (FAP) was measured in pike,Esox lucius, during embryogenesis and larval development at different temperatures. Chloroform-as well as methanol-soluble age pigments from eggs and larvae were quantified. Chloroform-FAP accumulated linearly with embryonic and larval development. After yolksack resorption, FAP concentrations reached a maximum and declined thereafter. Chloroform-FAP accumulation was not temperature dependent. Similar patterns of methanol-soluble pigment accumulation were found but accumulation of methanol-FAP was, in contrast, significantly temperature dependent. As a result, methanol-FAP concentrations increased in direct proportion to the rising incubation temperature, but the maximum methanol-FAP fluorescence was found at 15°C and not at 180°C.