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Cadmium (Cd) exposure can impair the traits of aquatic animals associated with reproduction. In natural lakes Cd is typically detected at concentrations below 0.001 mg l-1 . The authors investigated the impact of ultra-acute Cd exposure on sperm motility in European whitefish (Coregonus lavaretus). They activated sperm with water containing various nominal concentrations of Cd and recorded sperm motility parameters. Only the highest Cd concentration (500 mg l-1 ) was associated with decreased sperm swimming velocity and increases in both the percentage of static cells and curvature of the sperm swimming trajectory. The results indicate that environmentally realistic concentrations of Cd during the sperm motility activation are not critically harmful to male C. lavaretus fertilization potential.

This study revealed between-lake genetic structuring between Coregonus lavaretus collected from the only two native populations of this species in Scotland, U.K. (Lochs Eck and Lomond) evidenced by the existence of private alleles (12 in Lomond and four in Eck) and significant genetic differentiation (FST = 0·056) across 10 microsatellite markers. Juvenile C. lavaretus originating from eggs collected from the two lakes and reared in a common-garden experiment showed clear phenotypic differences in trophic morphology (i.e. head and body shape) between these populations indicating that these characteristics were, at least partly, inherited. Microsatellite analysis of adults collected from different geographic regions within Loch Lomond revealed detectable and statistically significant but relatively weak genetic structuring (FST = 0·001–0·024) and evidence of private alleles related to the basin structure of the lake. Within-lake genetic divergence patterns suggest three possibilities for this observed pattern: (1) differential selection pressures causing divergence into separate gene pools, (2) a collapse of two formerly divergent gene pools and (3) a stable state maintained by balancing selection forces resulting from spatial variation in selection and lake heterogeneity. Small estimates of effective population sizes for the populations in both lakes suggest that the capacity of both populations to adapt to future environmental change may be limited.

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to compensate for other yet unexplored mortality factors instead of having an additive effect on the present salmonids.

The probability that a fish matures at a certain age and length (the so-called probabilistic maturation reaction norm, PMRN) was analysed for a European whitefish Coregonus lavaretus species complex population living in the Austrian pre-alpine Lake Irrsee. Fish length was found to be the only relevant determinant of maturation probability, and females matured at slightly smaller sizes than males.

This study examined the potential biochemical and mechanical structures that may contribute to egg adhesion in European whitefish Coregonus lavaretus. Experiments showed that eggs from a population of C. lavaretus from Loch Eck remained non-adhesive in a solution chemically similar to ovarian fluid but became adhesive seconds after contact with water. Examination of the ultrastructure of the chorion showed that the morphology changed significantly after contact with water, with nodule-like protuberances attached to connective filaments on the surface present in water-hardened but not non-water hardened eggs. Biochemical analysis showed the presence of Chain A, RNase ZF-3e proteins in the chorion of water-hardened but not non-water hardened eggs. Histochemical staining of the chorion of C. lavaretus eggs showed that the externa, but not the interna, stained positively for the presence of glycoproteins. From these results, it was concluded that C. lavaretus from Loch Eck possess both anatomical and biochemical adhesive mechanisms that have been undocumented in this species so far.

Lamprey-induced scarring of the nationally rare Coregonus lavaretus, a known host of a freshwater-resident population of European river lamprey Lampetra fluviatilis, was found to have declined precipitously since the establishment of several non-native fishes in Loch Lomond. Evidence presented in this study points to the possibility that L. fluviatilis in this lake may have altered its trophic ecology in response to the negative impact that non-native species, in particular ruffe Gymnocephalus cernuus, have had on their favoured host.

This study examined how variability in the abundance and biomass structure of benthic invertebrates affected the feeding choice of the whitefish Coregonus lavaretus on a hard bottom habitat of the brackish Baltic Sea. In general, crustaceans such as Idotea balthica and Gammarus spp. were preferred over molluscs. Although being the most numerous taxon in the invertebrate samples, Mytilus trossulus was the lowest ranking in C. lavaretus food preference. The availability of benthic invertebrate prey set the dietary range of fish but the selectivity largely described fish feeding within this range. There was no clear link between fish predation and the dominance structure of benthic invertebrate communities, suggesting that species composition, abundance and biomass of invertebrate species had no impact on the feeding selectivity of the fish. Thus, while fish predation may not affect the dominant species within a benthic community, due to strong selectivity fish may impose strong pressure on some rarer but highly preferred invertebrate prey species.

The gonad morphology of whitefish Coregonus lavaretus collected in Lake Thun, Switzerland, and two neighbouring lakes was assessed in order to differentiate between 'normal' and 'abnormal' character states of gonad morphology, which had been previously described in C. lavaretus from Lake Thun (constrictions, asymmetries, aplasia, compartmentations, fusions and hermaphroditism). In total, 4668 fish were collected and analysed using two complementary sampling schemes: (1) monthly samples of catches by the commercial fishermen and (2) samples of ripe spawners of all known 33 spawning sites of the three lakes. Considerable variation in gonad morphology in C. lavaretus populations of all lakes was found. Notably, all deviation types were observed in fish of all three lakes. Asymmetries and constrictions were frequent in all three lakes and showed systematic differences in frequency between the two sampling strategies. This indicates that asymmetries and constrictions represent to a large extent natural variation in gonad morphology of C. lavaretus and are also prone to considerable measurement error. In contrast, aplasia, fusions, compartmentations and hermaphroditism occurred predominantly in one C. lavaretus form of Lake Thun and in particular in populations spawning at great depths. This suggests that these deviation types are probably reliable indicators for gonad deformations and supports the interpretation that Lake Thun harbours a unique case of deformed gonads in C. lavaretus of yet unknown origin.

International audience; The hypothesis that diatom carbon (C) produced during the spring peak supported spring zooplankton production and, ultimately, the growth of Coregonus lavaretus early larval stages from March to May 2006 in Lake Annecy, France, was tested using gut content analyses and fatty acid biomarkers. Gut content results showed that C. lavaretus larvae from stages 1 to 4 preferentially fed on copepods with Daphnia sp. only a minor proportion of larval diet. The levels of diatom-marker fatty acids (C16:1n-7 and C20:5n-3) were high in Daphnia sp., but lower in both copepods and C. lavaretus larvae from stages 0 to 4. These results indicated that the spring diatom biomass was actually grazed by Daphnia sp., but, contrary to what was expected, the spring bloom was not the only C source supporting copepods secondary production and, consequently, the growth of C. lavaretus early larval stages. In contrast, levels of terrestrial fatty acid marker (C24:0) were low in Daphnia sp. but high in copepods and C. lavaretus larvae, indicating a significant contribution of terrestrial carbon to copepods and, ultimately, to the growth of C. lavaretus early larval stages.

Source at https://doi.org/10.1111/j.1095-8649.2007.01678.x. Vendace Coregonus albula has invaded the subarctic Pasvik hydrosystem, northern Norway and Russia, after being translocated from its native Finnish range into Lake Inari (Finland), upstream of Pasvik. The development of the invader and the effects on two native lake communities in the upstream and downstream part of the hydrosystem, respectively, have been monitored since 1991. In the upstream lake location, the invader relegated the native whitefish Coregonus lavaretus from the pelagic habitat within a few years. An expected similar development in the downstream location was, however, not observed. Data are presented on the diet and microhabitat use (vertical pelagic zone) for three types of replicated situation: (1) the invader v. the native species, (2) upstream v. downstream lakes and (3) early and late invasion stages, to explore the outcome of the competitive interactions. The use of different microhabitats available within the deeper pelagic zone in the downstream location was observed to have delayed the negative effects on native whitefish, possibly enabling a persistent coexistence between the two species in the pelagic zone of this lake.

Three field-identified whitefish Coregonus lavaretus forms in Lake Muddusjarvi, Finland, were compared in morphology, diet and prey size. First, these forms were studied with univariate and multivariate analysis to assess morphological divergence at a higher resolution level than in the field. Second, stomach contents were analysed to estimate diet-overlap among forms. Finally, the relationship between prey size and morphology was examined. The whitefish were assigned to the initial field-classification with 99·2% and 98·8% accuracy for morphologic and meristic traits, respectively. The small sparsely-rakered form (SSR) had the shortest rakers and largest gillraker space, followed by the large sparsely-rakered form (LSR) with intermediate gillraker length and gillraker space, while densely-rakered whitefish (DR) had the longest rakers and smallest gillraker space. The two sparsely-rakered whitefish forms (LSR and SSR), consumed mainly benthic macroinvertebrates, while densely-rakered whitefish (DR), utilized pelagic food items. Average diet-overlaps between whitefish forms were low in June-September (Schoener's α = 0·02 − 0·23). Gillraker number and length were negatively correlated to prey length in the diet (r = −0·73, and r = −0·60), while gillraker space was positively correlated with prey length (r = 0·81). The fact that these whitefish forms were morphologically and ecologically segregated, and that gillraker traits probably have a functional value in food selection, further suggests that natural selection has been important in structuring life-history trajectories into divergent niche use.

Two laboratory rearing experiments with newly hatched European whitefish Coregonus lavaretus larvae were performed to study the effects of UV-B (280–315 nm) radiation on their survival and growth. The results indicate that under normal circumstances in Finnish lakes, enhanced UV irradiance will not be a threat to the survival of newly hatched European whitefish larvae.

The potential use of clove oil (eugenol) as an anaesthetic for Atlantic salmon Salmo salar, brown trout Salmo trutta, rainbow trout Oncohynchus mykiss, whitefish Coregonus lavaretus, perch Perca fluviatilis and roach Rutilus rutilus was examined at 5, 10, 15 and 20°C using three anaesthetic concentrations (varying from 20 to 200 mg l -1 ) at each temperature. Substantial species differences in sensitivity to clove oil were observed, even amongst congeners, and there may be some disadvantages (slow recovery and possibly mortality) with using clove oil for 0+ year whitefish and at low temperatures for perch and roach.

Habitat use of three sympatric whitefish Coregonus lavaretus forms was determined using hydroacoustics, pelagic trawling and epibenthic gillnetting in the subarctic Lake Muddusjarvi during the day and night in June, August and September. Whitefish constituted 97% of the numerical catches and whitefish with high number of gill rakers (DR) were the most abundant whitefish form. Forms with low numbers of gill rakers used only epibenthic habitats during both the day and night in all study periods: large whitefish with low numbers of gill rakers (LSR) dwelled mainly at depths 0-10 m, whereas small whitefish with low numbers of gill rakers (SSR) used deeper (>10m) habitats. LSR and SSR whitefish consumed mainly benthic macro-invertebrates during all study occasions. The planktivorous DR whitefish used both epibenthic and pelagic habitats, but vertical habitat selection varied both over time of day and season. In June, when light intensity was continuously high, DR whitefish did not perform diel vertical migrations. In August and September, when dark nights were distinguishable, DR whitefish ascended from the bottom to the pelagic at dusk to feed on zooplankton, and descended at dawn. DR whitefish used pelagic habitats only at the lowest light intensities during the night, which was probably related to the high predation risk from brown trout Salmo trutta.

The scales of whitefish Coregonus lavaretus were used in place of dorsal muscle, which necessitates killing the fish, to study food webs from the δ 13 C and δ 15 N isotopic ratios in the organic fraction. As scales are composed of tooth organic and calcified fractions, a protocol for scale decalcification was first devised. The δ 13 C and δ 15 N values of the decalcified scales were then shown to he closely correlated to those of the dorsal muscle, demonstrating that scales could be used in place of muscle to study food webs. Changes in the δ 13 C of whitefish were determined from a scale collection that extended over the period during which the trophic state of Lake Geneva was recovering.

According to logistic regressions derived for pike Esox lucius and burbot Lota lota, the probability of ingesting fishes in Lake Muddusjarvi, northern Finland, was 50% at 19·3 and 22·1 cm LT, whereas Arctic charr Salvelinus alpinus and brown trout Salmo trutta shifted to piscivory at the lengths of 25·7 and 26·4 cm LT. The specialist piscivores, pike and burbot, consumed more prey species and took a wider range of prey sizes than Arctic charr and brown trout. The prey length for all predators increased in relationship to predator length. Whitefish Coregonus lavaretus was the dominant prey species in the lake and in the diet of all the piscivorous species. The whitefish population was divided into three forms, of which the slow-growing, and the most numerous densely rakered whitefish form (DR), was selected by all predator species. This form also had the smallest average size and widest habitat range, utilizing both pelagic and epibenthic habitats. Two sparsely rakered whitefish forms (LSR and SSR) occupied only epibenthic habitats and had lower relative densities than DR. These forms, LSR and SSR, had a minor importance in the diet of predator species.

Infection patterns of trophically transmitted helminth parasites were compared with feeding ecology in two sympatric whitefish Coregonus lavaretus morphs from two lake systems in northern Norway. In both lakes, the pelagic morph was an obligate zooplanktivore, while the benthic morph utilized both the benthivore and zooplanktivore trophic niches. The differences in niche utilization between the two morphs were associated with differences in trophic morphology (gill raker numbers), suggesting that they were genetically dissimilar and reproductively isolated. The benthic morph had the highest number of helminth species, probably because they exhibited a broader niche width compared to the pelagic morph. In both lakes, the species composition and intensities of helminths reflected the trophic diversification of the whitefish ecotypes with respect to different habitat choice (benthic v. pelagic) and dietary specialization (benthivore v. zooplanktivore feeding strategies within the benthic whitefish morph). Zooplanktivorous fish from both morphs acquired parasites mainly from pelagic copepods and in almost equal quantities. The benthivore feeders within the benthic morph had the highest proportion of parasites with transmission stages from benthic organisms. Host feeding behaviour seemed to be a major determinant of the helminth community structure, and helminths appeared to be useful indicators of long-term trophic specialization of whitefish ecotypes.

The food of five whitefish stocks Coregonus lavaretus planted in Lake Vuokalanjarvi consisted mainly of zooplankton and insects taken from the water surface. The amount of benthic food in the diet of the two sparsely gill-rakered (23 and 28 rakers) stocks increased from the age of 2 years onwards. The growth of whitefish was slow in all stocks. The densely gill-rakered stock (50–51 rakers) originating from the same lake system as Lake Vuokalanjarvi grew faster than the other stocks, and the food consumption of 4- and 5-year-old fish belonging to this stock was nearly double compared with the other stocks. The habitat choice of the whitefish differed between the stocks even in the densely-rakered stocks classified as the same form. A stock with flexible habitat use and feeding habits is most likely to succeed. Introducing whitefish stocks from distant areas is not advisable.

The prevalence of Diphyllobothrium ditremum plerocercoids in whitefish Coregonus lavaretus ranged between 70 and 100% in Lake Kilpisjarvi and in three other lakes in Northern Lapland, Finland. The mean abundance in Lake Kilpisjarvi (age groups 1+-10+ years), ranged between 103·5± 71·3 in 1992–1993 to 110·9± 80·0 plerocercoids per fish in 1997. The asymptotic value of the infection levelled at 113 plerocercoids per host after age 3. No significant difference in abundance was detected between study years (P>0·10). Abundances in other lakes ranged between 4·8±9·7 and 91·1±115·1. Two seasonal peaks of plerocercoid recruitment were observed in Lake Kilpisjarvi; between March and April (P

Patterns of accumulation of Triaenophorus crassus in its second intermediate host whitefish Coregonus lavaretus s.l. were studied between 1991 and 1996 from two host populations in two separate areas of Lake Saimaa, Finland. Whitefish were infected commonly with several T. crassus plerocercoids and the parasites were aggregated into the oldest hosts. In one host population the annual parasite accumulation was 0·9 parasites in all host age groups between 3 and 8 years. In the other host population the annual accumulation was 1·6 parasites in 3–5-year-old fish, but increased up to 3 to 4 parasites per year in fish over 5 years old. The increase did not coincide with the period of maturation or any increase in whitefish growth, both of which could alter the food intake of the fish. The sharp increase in the annual accumulation suggests a threshold intensity above which the probability of acquiring further parasites increases. In spite of a heavy aggregation of parasites there was no evidence of parasite-induced host mortality. The annual increase in mean abundance was not correlated with the mean annual weight increase in 2–4-year-old fish within cohorts. However, evidence of a negative effect of parasites on whitefish growth was revealed by back-calculation of lengths of uninfected and infected whitefish and correlations between length or weight of fish and intensity of infection with fish age. Both analyses suggested that larger young fish harboured more parasites than the smaller ones while in older fish the reverse was true, a pattern that has not been shown earlier for parasitized fish.

The whitefish, Coregonus lavaretus, is a schooling species, and it was hypothesized that, when faced with feed restriction, the behaviours associated with a schooling habit would lead to there bein ...

Food consumption and energy allocation of larval and juvenile whitefish Coregonus lavaretus L. were studied by conducting respirometry experiments at 10, 12 and 15) C. Results from these experiments were compared with those predicted by a bioenergetics model that used observed growth as the major input. The data were used to assess the performance of the model, and evaluate its suitability for estimation of food consumption by whitefish. The mean absolute % error (Â) between observed and predicted food consumption was 16·3%, and the modelling eYciency (ME) was 0·90, indicating that the model was reasonably robust. Linear regression analysis of predicted v. observed food consumption values gave a slope slightly above unity, indicating a tendency for the model to overestimate consumption at higher values. Â and ME were also calculated for total metabolic rate (RT), and they equalled 13·0% and 0·85, respectively. Despite some deficiencies, it is concluded that the model can be used for prediction of food consumption by highly active, planktivorous fish such as whitefish. ? 1998 The Fisheries Society of the British Isles

Perch Perca fluviatilis and roach Rutilus rutilus were caught at various locations around Lake Constance (Bodensee). Infection of perch and roach with the eyeflukes Diplostomum spathaceum and Tylodelphis clavata was greatest in the western location (Bottighofen). The varied occurrence of parasite species at different locations indicated that maximum interchange between fish populations was slight. Whitefish Coregonus lavaretus migrating up the River Rhine were less infected with both the tapeworm Proteocephalus exiguus and the copepod Ergasilus sieboldi than whitefish from the middle of the lake. Some of the parasites had already left their hosts. Newly established infections were not found in migrating whitefish.

The temperature relationship of routine metabolic rate (Rr) of non-feeding, non-growing Coregonus lavaretus larvae between 2 and 15°C is characterized by Q10-values ranging from l.8-2.45. The rate of growth, based on weight determinations, of first-feeding larvae amounted to 3.5, 7.6 and 9.4% day-1 at 5, 10 and 12°C respectively, from which Q10-values between 4.0 and 4.8 can be calculated. The rate of increase of muscle mass between 5 and 10°C, based on the determination of the cross-sectional area of inner muscle fibres, resulted in a Q10-value of 4.5. Water temperature influenced the pattern of growth of the inner muscle fibres. At hatching, after 360 day degrees, total muscle mass of larvae reared at 4 and 8°C was independent of temperature, but at 4°C the rate of mass increase owed more to hyperplasia (increase in fibre number) than to hypertrophy (increase in fibre mass), whereas at 8°C the opposite was the case. The calculation of power budgets (including the metabolic cost of growth) of first-feeding larvae yielded net conversion efficiencies (K2) increasing with temperature from 46.3% at 5°C to 54.7% at 12°C. Comparing our data with literature data two general conclusions can be drawn. (1) In first-feeding larvae the net, but not the gross, conversion efficiency of food energy increases with temperature. This is due to net energy input being characterized by a much higher Q10-value than energy expenditures. (2) In embryos of freshwater fish so far investigated hyperplasia plays a greater role in the increase of fibre mass than hypertrophy at the lower temperature, whereas in embryos of marine fish hyperplasia prevails at the higher temperature. It is suggested that this discrepancy correlates with the high concentration of free amino acids in the eggs of marine species which provide an additional, easily available, source of metabolic energy absent in freshwater species.

The whitefish Coregonus lavaretus is confined to two Scottish lochs and four English and one Welsh lake in the British Isles. Restriction fragment length polymorphisms (RFLPs) in the mitochondrial (mt) DNA have been used to analyse variability within and between populations. The 14 restriction enzymes employed in this study examined approximately 3% of the mt genome and revealed 15 haplotypes among 156 fish. Haplotype diversity within populations was generally low except for the Welsh population where nine haplotypes were found among 30 fish examined. The haplotypes clustered into three distinct groups corresponding to Scottish, English and Welsh populations. No haplotypes were shared among the three groups. Possible alternative explanations for these findings are introgression from another species, stochastic lineage sorting from a polymorphic ancestral gene pool and/or separate colonizations following the last glaciation.

Proportion of loci polymorphic (P) and mean heterozygosity per locus (Hexp) were P= 0.130 and Hexp= 0.096 for C. albula from the English Lake District and P= 0.217 and Hexp= 0.046 for C. lavaretus from the English Lake District and Llyn Tegid, Wales in 1991–2. Significant deviation from the Hardy-Weinberg model was observed at the superoxide dismutase (sSOD*) locus in C. albula from Bassenthwaite Lake. This could have been due to chance, to the Wahlund effect or to selection. Genetic distances between the two species were consistent with their taxonomy and genetic differentiation was much greater for the C. lavaretus populations than for the two geographically close C. albula stocks. Llyn Tegid C. lavaretus showed unique alleles at two loci and conservation of fish in this lake is therefore of great importance. Red Tarn C. lavaretus differed most from other Lake District populations probably due to founder effects from early stocking events and/or from selection due to the high altitude of this lake.

A key for three putative species apparently found in three geographic areas, i.e. Coregonus clupeoides (in Scotland), Coregonus stigmaticus (in England), and Coregonus pennantii (in Wales) given in a recent review was tested quantitatively using 544 individuals from nine populations. The classification success of the key was very low (27%). It was concluded that there is currently no robust evidence for the recognition of the three putative species. Furthermore, the use of phenotypic characters alone to distinguish putative species in postglacial fish species such as those of the genus Coregonus that show homoplasy in many of these traits is questioned. In the absence of further evidence, it was concluded that a single highly variable species best describes the pattern of phenotypic variation in these U.K. populations. On this basis it is argued that taxonomic subdivision of U.K. European coregonids is inappropriate and that Coregonus lavaretus should prevail as the species name applicable to all populations.

About 20 ovaries of the whitefish ‘Blaufelchen’ (Coregonus lavaretus L.) of Lake Constance (Bodensee) were collected annually from 1964-1991. Absolute and relative fecundity peaked in the early 1980s, lagging about 2 years behind the maximum of total-P in the water (during the circulation period). Out of the biological time-series of Lake Constance, whitefish fecundity is the only one known to follow the phosphorus curve, and this may be the first time-series documented case of parallel trend reversal in the trophic state of a lake and fish biology. It is concluded that fish fecundity serves, at best, as an unspecific monitor of the overall well-being of the fish.

Differences in stable-isotope values, morphology and ecology in whitefish Coregonus lavaretus were investigated between the three basins of Loch Lomond. The results are discussed with reference to a genetic investigation to elucidate any substructuring or spawning site fidelity. Foraging fidelity between basins of Loch Lomond was indicated by +¦13C and +¦15N values of C. lavaretus muscle tissue. There was, however, no evidence of the existence of sympatric morphs in the C. lavaretus population. A previous report of two C. lavaretusGCyspeciesGCO in Loch Lomond probably reflects natural variation between individuals within a single mixed population

The adverse effects of high temperatures on the early life stages of anadromous whitefish Coregonus lavaretus were experimentally examined by assessing fertilization success, the percentage of developmental abnormalities, cumulative mortality and the rate of embryogenesis across a range of temperatures. Temperatures >or= 7 degrees C increased the proportion of unfertilized and abnormally dividing eggs, deformed embryos and consequent mortality. The higher the temperature, the more severe were the effects. When eggs were fertilized and constantly incubated at various temperatures, the effective level for 50% of the eggs and embryos (EL50) of temperature was 7.6 degrees C at the developmental stage when eye pigmentation was visible. Fewer developmental abnormalities and a lower cumulative mortality rate were observed when embryos were exposed to high temperatures from the later, gastrula stage, than from fertilization or the four-cell stage. Irrespective of retarded development in terms of day-degrees (i.e. the sum of daily mean temperatures), a high incubation temperature reduced the development time of C. lavaretus, leading to earlier hatching, and hatched fry were shorter than at the reference temperature of 4-5 degrees C. Global warming will particularly pose risks for stenothermic species such as C. lavaretus, with early life stages being especially susceptible. Thus, relatively small increases and fluctuations in river water temperatures during the spawning season of this anadromous species may have substantial negative impacts on its recruitment and population persistence.

Anadromous whitefish [Coregonus lavaretus (L.)] yolk-sac larvae were marked with a radioactive strontium isotope, 85Sr. Before marking the method was tested in accumulation-elimination tests using various strontium concentrations. The first-phase effective half-life of 85Sr in yolk-sac larvae was 4 days. The mean 85Sr radioactivity was 81 Bq per larva at the day of release and the half-life of the slow component was 51 days, so the strontium label was easily detected up to 60 days after marking. The larvae were released into the River Simojoki about 12 km upstream from the river mouth and recaptured from early May to the end of July. Marked larvae were found at the river mouth 12–13 days after release, while the last marked fish in the river were found at 16 days. It is likely that all leave the river within 2 to 3 weeks post-hatching. Two months after marking some larvae had attained a distance of 10 km from the river mouth.

Rapid and dramatic change in the fish community of Loch Lomond has resulted from a series of fish introductions in recent years. A comparison of the diet of pike, Esox lucius L., in 1989–1990 with data from 1955–1967, prior to recent introductions, demonstrates a shift in prey choice. In 1955–1967 powan, Coregonus lavaretus (L.), dominated in the diet (57% of prey by number) by 1989–1990 the introduced ruffe, Gymnocephalus cernuus (L.), was the commonest prey species (44% by number). This shift in pike predation to an abundant population of introduced ruffe has consequences for native species. Assuming that the pike population has not increased in response to increased food availability due to the introduction of ruffe, pike predation pressure on native species will be relieved. This is likely to have the greatest effect on powan. Comparison of the predation rate in 1955–1967 with 1989–1990 supports the hypothesis that the rate of predation on powan has declined, although the effect that this may have on the powan population is unclear, as the role of predation in the regulation of population size is unknown for this species.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.

Juvenile whitefish, Coregonus lavaretus (L.), wet weight 0.04 to 5.2 g, from Lake Constance were kept at 10, 12 and 16° C water temperature, respectively and fed with living zooplankton. The experimental duration lasted 72 to 120 h. Daily rations were defined as the amount of zooplankton remaining subtracted from the amount of zooplankton added after a 24 h interval. The mortality of the zooplankton was determined in parallel experiments without fish. Relative daily ration (zooplankton weight/fish weight) v. fish weight increased up to a fish dry weight of approximately 0.12 g and then decreased steadily. The maximum daily ration was about 270% of fish body wet weight (wet/wet) corresponding to 75% of body dry weight (dry/dry), respectively. In fishes of a dry weight higher than 0.12 g (wet weight 0.65 g) a significant difference in food intake was found between 12 and 16° C. The specific growth rate ranged from nearly 0 up to 33% per day. No correlation was found between daily ration and specific growth rate.

The presence of the nationally-rare schelly. Coregonus lavaretus, in Brotherswater, a small lake in the English Lake District, was confirmed in the summer of 1992. However, pronounced deepwater oxygen depletion may pose a threat to the continued survival of this seventh U.K. population.

The gastric evacuation of juveniles of Coregonus lavaretus L. fed on living Daphnia pulicaria was investigated. Three successive stages of stomach evacuation were observed when one meal per day was given: (i) a lag phase between the end of food intake and the beginning of stomach evacuation, (ii) a linear reduction of stomach content, (iii) a long residence time for food relics in the stomach. The initial stomach content and the stomach evacuation time are correlated positively. The stomach content increased during feeding when three meals day −1 were provided and it decreased when no food was available. During the course of an experiment the highest stomach content found increased with increasing daly ration. Excess feeding resulted in a low stomach content similar to that found with rations about 30–50% of the maximum daily food intake. Therefore the daily food intake cannot be determined by the single parameter of stomach content alone. Identical initial stomach contents showed significantly higher stomach evacuation rates under three meals day−1 conditions than under one meal day−1 conditions.

The milt composition of six freshwater teleosts was studied, and the measured parameters showed clear specific differences between species. The highest spermatocrits and sperm densities were observed in perch, Perc afluviatilis, and burbot, Lota lota, and the lowest in rainbow trout, Salmo gairdneri, and whitefish, Coregonus lavaretus. Fructose concentrations in the seminal plasma were small compared to mammalian values. The glucose concentrations in the seminal plasma were five times higher than those of fructose, and higher in landlocked salmon and rainbow trout than in the other species. The citric acid concentration of all species except whitefish showed a significantly positive correlation to either spermatocrit or sperm density. The role of citric acid in the seminal plasma of fishes was also assumed to be important. The glycerol concentration in the seminal plasma was comparatively high, and highest in whitefish. This was assumed to be related to the high applicability value of glycerol as a cryoprotective agent for whitefish sperm. The high glycerol concentration was also assumed to be related to the lipolytic capacity of the testis in the studied species.

A total of 206 river-spawning whitefish Coregonus lavaretus (L.) from the Bothnian Bay was investigated for food objects and acanthocephalans in the years 1975–78. The only acanthocephalan species found was Metechinorhynchus salmonis (Muller 1780), the total number of which was 1295. The whitefish is shown to be highly susceptible to infection by M. salmonis, with as many as 88·9% of specimens infected in a sample in June 1978, although the mean intensity was only 8·9 parasites per host. The river-spawning whitefish does not favour the intermediate host, Pontoporeia affinis, in its summer diet in the Bothnian Bay preferring to feed on eggs and molluscs, so that the incidence of M. salmonis infection decreases to 33·3% by the middle of summer. This is further reduced in the late summer by the fast associated with the migration to their upriver spawning grounds. The fact that the other acanthocephalan inhabiting the river-spawning whitefish in the southern Gulf of Bothnia, Echinorhynchus gadi Muller, 1776 is not to be found in the Bothnian Bay population suggests that the fish captured in spring have remained in the Bothnian Bay throughout the winter.

Using histochemical methods, morphofunctional aspects of the alimentary tract of larval coregonids were investigated. Larvae of Coregonus lavaretus were reared for 34 days with either zooplankton or one of two dry diets. Ontogeny, localization and diet-related modifications of the following enzymes were examined: trypsin (luminal digestion), aminopeptidase, maltase, alkaline phosphatase (brush border-bound digestion) and unspecific esterase (intracellular nutrient processing). All of the enzymes studied were present in 13-day-old larvae. Except for the intracellularly located unspecific esterase, there was an ontogenetic enhancement of enzyme staining intensities accompanied by a significant increase in the volume of the intestinal mucosa. Enzyme activities differed within and between intestinal regions. This finding suggests that a spatial gradient of nutrient breakdown and absorption already exists in the morphologically and physiologically incompletely developed digestive system of larval coregonids. Digestive enzyme activities were modified in response to the dietary regimen. There was no obvious correlation between enzymic response and growth performance of the larvae.

A direct comparison of plasma cortisol levels and mean nuclear diameter of adrenocortical cells in the same fish was carried out, to determine whether nuclear diameter could be used as a valid criterion of adrenocortical activity in Coregonus lavaretus (L.). Specimens were caught and killed by a variety of methods and at different seasons, providing a range of plasma cortisol concentrations, which were measured by gas-liquid chromatography. The head-kidneys of the same fish were immediately fixed and the diameters of 20 adrenocortical cell nuclei measured in 7 μm sections of each, prepared by strictly standardized methods. The correlation coefficient was 0·54, so that nuclear diameter cannot be regarded as an accurate criterion of adrenocortical activity.

Some aspects of the biology of the schelly Coregonus lavaretus (L.) were investigated by examining 188 that had passed down an aqueduct from Haweswater and 437 that were caught in gill nets set in Ullswater. In both lakes the main breeding season is from mid January to mid February, and in Ullswater spawning takes place in shallow water [less than 7.6 m (25 feet)] on a sandy bottom with stones and weed, at the entrance to a bay. The males in Haweswater first spawn when 3 years old and in Ullswater when 2; and the females first spawn in Haweswater when 4 years old, and in Ullswater when 3. Scales were kept from every fish and were found suitable for age determination. Some Haweswater schelly live for 9 years, but from Ullswater the oldest was 8. The rate of growth of male Haweswater schelly was very well described by the equation: (where lt(=the length at time t) but the curve had to be transposed a further year to describe adequately the Ullswater male schelly growth. It is clear that the rates of growth are similar in the two lakes after the first year, during which it is much faster in Ullswater. A study of the length-weight relation showed that the weight is proportional to the length cubed, and no difference in condition was found between males and females. The schelly egg was found to be slightly sticky, spherical and 2.98 mm in diameter. Some fertilized eggs were kept at various constant temperatures. At 4°C and 6°C the death rate was low, but was higher at 8°C and total mortality occured at 10°C. This low upper lethal temperature probably restricts the spawning season to mid-winter and also limits the species' geographical range, as has also been suggested for the char Salvelitms alpinus (L.) whose eggs have similar temperature requirements. Some eggs were reared to adults, and these provided corroboration of the validity of the scales for age determination. Two other points mentioned in this paper were the occasional winter strandings of schelly, and the incidence of a supernumerary pelvic fin.

A single hermaphrodite specimen of Coregonus lavaretus (L.) was caught mid-January in Loch Lomond, Scotland.