Populational variability of Proteocephalus longicollis (Cestoda: Proteocephalidae) in the vendace Coregonus albula from lakes of Karelia

Populational variability of Proteocephalus longicollis from the vendace inhabiting various types of Karelian water bodies was studied. High phenotypic diversity of the helminth and polymorphism in the cestode's major functional complexes - attachment, trophic and reproduction - are established. High degree of phenotype pool realization was determined for various P. longicollis populations. Traits belonging to different functional complexes were shown to have different variability patterns. The highest stability was shown for the attachment organs of P. longicollis, which had similar values of qualitative indices and nature of variation. The traits of the trophic and reproduction complexes are more variable. The conclusion was made that the high intrapopulation diversity of P. longicollis is a response to high ecological variability of the vendace, and the distinctions in the phenotype variability of the helminth reflect the differences between population development patterns of the parasite (cestode P. longicollis) and its host (vendace Coregonus albula) in lakes of Karelia.     

Morphological polymorphism of the cestode Proteocephalus longicollis Zeder, 1800 (Cestoda: Proteocephalidae) through the ontogeny

The qualitative diversity of Proteocephalus longicollis through the ontogeny was studied: procercoids from copepods, immature and mature cestodes from the vendace Coregonus albula L. The structure of the P. longicollis population was found to be made up of the dominant phenotypes: by the scolex shape--Sc2, by the sucker arrangement type--SI, by the proglottid shape--P3, by the ovary lobe shape--01, by the testes arrangement type -T2. Some rare and scant phenotypes are also present. It is shown that the structure of the parasite phenotypes is relatively stable through the ontogeny. The assumption is made about the high survival rate of the S2 sucker phenotype.     

Successional features of the dynamics of abundance and population structure of the cestode Proteocephalus longicollis (Zeder, 1800) (Cestoda: Proteocephalidae)

Dynamics of abundance and changes of populations structure were investigated in a host-specific parasite of salmonids, cestode Proteocephalus longicollis from the vendace Coregonus albula L. of the Syamozero Lake during the period of more than forty years. A relative stability of the values of infestation indices independently of significant changes in the abundance and population structure of the vendace is established. Changes in the distribution of abundance and population structure of P. longicollis are shown to be connected with the change of the water body's status resulting from eutrophication. These changes can be considered as reliable indices of the succession in freshwater bodies.     

Reinvestigation of spermiogenesis in the proteocephalidean cestode Proteocephalus longicollis (Zeder, 1800)

The reinvestigation of spermiogenesis in the proteocephalidean cestode Proteocephalus longicollis (Zeder, 1800) provides new details that were not described previously for this species. The 2 centrioles with roots are oriented at the first tangential to the long axis of the nucleus in a differentiation zone. They come to be arranged in the same plane only when a single intercentriolar body (ICB) appears between them. The ICB had been described previously as consisting of a number of dense elements (Swiderski, 1985) but, in the present study, appeared as a single, electron-dense plate. Also new for this species is the observation of 2 arching membranes that appear at the base of the differentiation zone only when the 2 flagella rotate toward the median cytoplasmic protrusion. Moreover, the formation of a crested body is described for the first time in P. longicollis. The present data support the suggestion that the process of spermiogenesis in proteocephalidean tapeworms corresponds in most features to that observed in some members of the unrelated tetraphyllidean clades, the Onchobothriidae and Phyllobothriidae. This may represent more evidence regarding the close relationship between tetraphyllidean and proteocephalidean cestodes, but existing information is fragmentary and controversial in some characters.     

Mitochondrial DNA sequence from an extinct population of European vendace, Coregonus albula L

Nucleotide sequence of the mitochondrial DNA control region was determined for the formalin-preserved specimen of the individual European vendace, Coregonus albula, belonging to an extinct population. The specimen has been preserved and stored in formalin for 39 years. A comparison with two previously determined sequences obtained for specimens from other populations of vendace revealed both nucleotide substitutions and site heteroplasmy. The ability to sequence DNA from formalin-preserved museum specimens of rare or extinct taxa provides another sampling strategy for phylogenetic studies on fish.     

Seasonal dynamics of the extent of the infestation of the vendace by the cestode Proteocephalus exiguus (Cestoda, Proteocephalidae) in Karelia

In two lakes of Karelia the infection dynamics of vendace (Coregonus albula L.) with the cestode Proteocephalus exiguus (La Rue) was studied in the summer-autumn period. 2006 specimens of vendace were dissected. Regularities of variations in the infection extensiveness depend on ecological characters of a water body and are modelled by various polynomes.     

Temperature requirements for growth and survival of larval vendace, Coregonus albula (L.)

Water temperatures from 15.0 to 20.0° C are recommended as the most suitable for sustained production of larval vendace, as indicated by the developmental rates, the instantaneous rates of growth, mortality, and the net biomass gain of larvae reared at eight constant temperatures from 4.8 to 22.1° C. The recommended temperatures are optimal when the available food and photoperiod are not the limiting factors. Temperatures higher than 22.0° C will cause increased mortality, whereas temperatures lower than 15.0° C, although advisable when food is limited, will retard larval growth and development.     

Survival, growth and feeding of vendace, Coregonus albula (L.), larvae in net enclosures

Vendace, Coregonus albula (L.), larvae reared in net enclosures anchored in the littoral zone of Lake Ylä-Enonvesi, eastern Finland, were observed for a period of 44 days in order to determine the effects of density on mortality, growth and feeding of the larvae. The ratio of newly-hatched fish to their food was regulated by controlling the number of fish stocked into the enclosures. Prey animals were expected to move freely in and out of the enclosures. The effect of nylon mesh (500 μm) on the penetration of zooplankters into the enclosures was negligible. The influence of possible starvation was determined by analysing the growth of the larvae, their Fulton condition factor, the instantaneous amount of food ingested, and the food composition in their guts. All these indicators were inversely correlated with larval density. Vendace larvae were found to be resistant to mortality from direct starvation. At all densities the survival rate was over 60%. At the time of complete yolk absorption, there was no increase in mortality.     

Digestion of zooplankton in the alimentary tract of vendace (Coregonus albula) larvae

The degradation of zooplankton eaten by vendace larvae was investigated by cutting their tubiform alimentary tract into four quarters and analysing the contents separately. Soft-bodied rotifers were found to degrade and become indistinguishable in the anterior part of the alimentary tract, while cladocerans and copepods could still be identified in the posterior part. Assessing the diet of a larva on the basis of its whole alimentary tract contents was found to give biased results. More reliable estimates of the proportions of zooplankton taxa in the diet could be achieved from the first quarter of the alimentary tract.     

A multidisciplinary approach to the systematics of Proteocephalus macrocephalus (Creplin, 1825) (Cestoda: Proteocephalidae)

The tapeworm Proteocephalus macrocephalus (Creplin, 1825), a parasite of the eel Anguilla anguilla, was characterised using morphological and genetic characters. The species is morphologically typified mainly by features of the scolex (i.e. shape and size of an apical organ which is formed early during the development in an intermediate host) and strobila (i.e. regularly rectangular proglottides, morphology of the vagina and anterior position of the seminal receptacle). Genetically, P. macrocephalus was compared with two congeners, P. percae and P. exiguus. Characters enabling differentiation of P. macrocephalus were as follows: fixed allelic differences at Got, Pgm and Gapdh loci, metrical features of chromosomes Nos 1, 2 and 7, and species-specific fragments obtained by RAPD method using 13 random primers.     

Species of Proteocephalus Weinland, 1858 (Cestoda: Proteocephalidae) from cyprinid fishes in North America

A taxonomic study of Proteocephalus species parasitizing cyprinid fishes in North America, namely Proteocephalus ptychocheilus Faust, 1920 and Proteocephalus cobraeformis Haderlie, 1953, has demonstrated their conspecificity with Proteocephalus torulosus (Batsch, 1786), a common parasite of cypriniform fishes (Cyprinidae and Cobitidae) in the Palaearctic Region. Proteocephalus ptychocheilus and P. cobraeformis are considered junior synonyms of P. torulosus.     

Egg quality and female condition in vendace (Coregonus albula L.) before and during spawning

The fat content of muscle, liver and eggs of vendace (Coregonus albula L.) were measured during the maturation of ovaries in summer. The fat content of eggs was at its highest in July and that of muscle in August during the optimal feeding season. Significant differences were not found in fat content between lakes Suvasvesi and Southern-Kallavesi in central Finland. There were no essential differences in fatty acid composition between muscle, liver and eggs of Lake Suvasvesi vendace. During the last month before spawning in October the gross energy and fat contents of eggs decreased in Lake Suvasvesi vendace. The fat and vitamin C contents of muscle as well as the liver index of females decreased during this time also. In males the corresponding decrease did not occur, indicating that spawning is a greater stress for females than for males. The egg quality and condition of Lake Inarijärvi vendace were about the same as those of Lake Suvasvesi vendace. The unfavourable conditions of Lake Inarijärvi, located in northern Finland, are reflected in the size of ovaries, which is known to be smaller (gonadosomatic index < 20%) than in Lake Suvasvesi (GSI 26–27%). Vendace, then, maintain the quality of eggs at the expense of their number.     

Experimental estimation of the food intake of larval vendace (Coregonus albula L.) under field conditions

We estimated the food intake of larval vendace (Coregonus albula L.) directly in an experimental chamber under field conditions. The larvae were stocked into net enclosures and reared without additional feeding for 6 weeks immediately after the ice melted in Lake Ylä-Enonvesi, Eastern Finland. The food intake was estimated on the basis of the decrease in zooplankters due to larval predation in the transparent plastic chambers anchored in the littoral zone. The experiments were carried out twice in 1988 and three times in 1989 (May–June). The numbers of zooplankters inside the chambers were counted from the subsamples using an inverted microscope. The relative daily ingestion rate (mg dry mass of prey animals mg dry mass of fish ^–1 24 h^–1) of the larvae of different sizes was: 1.09 and 0.84 for 9–11 mm larvae, 1.27 for 11–13 mm larvae and 0.34 for 17–20 mm larvae. The measured ingestion rate is presumed to be near the maximum consumption of the larvae. This method could provide accurate estimates of food consumption in the field or in the laboratory.     

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

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.     

Common sculpin Cottus gobio as a natural paratenic host of Proteocephalus longicollis (Cestoda: Proteocephalidae), a parasite of salmonids, in Europe.

Common sculpins Cottus gobio L. (Pisces: Cottidae), from the Mlynsky Brook near Ceské Zleby in the Sumava National Park, southwestern Bohemia, Czech Republic, were found to harbour in their intestines juvenile cestodes Proteocephalus longicollis (Zeder, 1800), a common parasite of holarctic salmonids, with a prevalence of 60% and intensity of 1 to 11 (mean 5) parasites per fish; undoubtedly, these prey fish serve as paratenic hosts. In this locality, the definitive host of P. longicollis is the brown trout Salmo trutta m. fario L., large specimens of which apparently acquire infection of this parasite by feeding on infected sculpins. C. gobio is the first known natural paratenic host of P. longicollis in Europe.     

Food consumption of vendace Coregonus albula larvae in Lake Lentua, Finland

The daily ration of vendace larvae (mean TL 10·1–12·8 mm) was assessed after a time-intensive field survey in Lake Lentua. Ten larvae were sampled every 2 h throughout the 10-day sampling period and their alimentary tract contents analysed. The gut was cut into four quarters of equal length and each quarter was analysed separately. This procedure enabled the assessment of the proportions of different zooplankton taxa in the diet based on the least degraded first-quarter contents and to reconstruct the entire gut contents. Secondly, the gut passage time of ingested zooplankton was evaluated by comparing the degradation rate of zooplankton in the guts of experimentally fasted larvae to the degradation of zooplankton in the gradient from pharynx to anus among the larvae sampled from the lake. Finally, food consumption was calculated as zooplankton individuals and carbon biomass based on the two variables, gut passage time of constantly feeding larvae and reconstructed gut contents. The daily ration of vendace larvae varied between 14 and 450 zooplankters in the monitored period.     

Year-class fluctuations in vendace,Coregonus albula (Linnaeus): Who's got the upper hand in intraspecific competition?

The vendace Coregonus albula (L.) populations in the lakes Mjøsa and Osensjøen exhibited fluctuating year-class strength. In Mjøsa, a strong year-class emerged every third year, except for the four year period between the strong year-classes 1969 and 1973. The difference between the strong and weak year-classes decreased from the 1960s, through the 1970s to the 1980s. The Mjøsa vendace matured sexually at age 2 +, and more than ten sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 23.6 cm. In Osensjøen, one strong year-class (1969) dominated the population during the period 1976–1987. The Osensjøen vendace matured sexually at age 3, and more than 15 sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 28.4 cm. In both lakes, vendace fed on crustacean zooplankton in the epilimnion throughout summer and autumn. Our data indicate that regular year-class oscillations occur as a result of the juvenile survival being negatively correlated to the number of adults.