The abundance and distribution of Diphyllobothrium dendriticum (Nitzsch) and D. ditremum (Creplin) in the char Salvelinus alpinus (L.) in Sweden

A total of 654 char, Salvelinus alpinus (L.) and 33 brown trout, Salmo trutta L., were examined for the plerocercoids of Diphyllobothrium dendriticum (Nitzsch, 1824) and D. ditremum (Creplin, 1825). Only char were found to be infected. Both parasitic species were abundant. The incidence and mean intensity of infection for D. dendriticum were 83.2% and 8.8, respectively; for D. ditremum 93.7% and 45.0. There was no variation in the intensity of infection between different parts of the lake. The incidence and intensity of infection increased with the age of the fish to age 8+ for both species. From this age the intensity of infection leveled off or decreased. No differences in intensity of infection between the sexes were found. The frequency distribution of parasite counts were overdispersed and fitted the negative binomial distribution even within single age-groups. The two parasite species showed a high positive correlation in intensity of infection, D. ditremum was concentrated in the stomach and pyloric caeca. D. dendriticum was more widely distributed within the host and was supposed to kill heavily infected fish.     

Egg size and form as taxonomic criteria in Diphyllobothrium (Cestoda, Pseudophyllidea)

The size and form (length, width, and length: width ratio) of eggs of Diphyllobothrium dendriticum, D. ditremum and D. latum vary considerably among individual worms within each species. The size of eggs varies with host species and a decrease in egg size with increasing intensity of infestation is indicated. The egg size of D. latum increases during the first 10-12 days of egg production. For single worm infections in golden hamsters the mean egg length and width of D. ditremum are significantly smaller than the corresponding means of D. dendriticum and D. latum, while D. latum has significantly wider eggs than D. dendriticum. As taxonomic characteristics, egg size and form may contribute to species delimitation at the population level. For identification at the individual level the best possible accuracy is about 80%. This accuracy is considerably reduced when variation in host species and intensities of infestations are introduced. Scanning electron microscope studies did not reveal any differences among eggs of the three species.     

Ultrastructural studies on Diphyllobothrium ditremum and D. dendriticum (Cestoda, Pseudophyllidea), with emphasis on the scolex tegument and the tegument in the area around the genital atrium.

The scolices of D. ditremum and D. dendriticum are similar in regard to general morphology and ultrastructure of the tegument. At the scolex apex and along the upper bothrial edges sensory endings are numerous. The inner bothrium surface of D. ditremum appears to be plain or smooth, the distal cytoplasm is only about 0.6 mum thick and covered with long and slender microtriches. When D. ditremum is attached to the host gut an adhesive layer of secreted substance exists between the inner bothrium surface and the host intestinal villi. In D. dendriticum, however, no secreted layer exists between the inner bothrium surface and the host intestinal villi and the inner bothrium surface of this species appears to be lobed or lappet formed. The lobes are protrusions of the distal cytoplasm and are covered with long and slender microtriches. Large conglomerations of secretion globules appearing to be enclosed by a double membrane, are observed in the scolices of D. dendriticum and D. ditremum, although more frequent in the latter. Differences existing between the distal cytoplasm of the scolex and the gravid proglottid are described. The papillae around the genital atrium in mature and gravid segments were studied. Each papilla appears as a thickening of the distal cytoplasm, which in this region is 10-12 mum thick, when studied with transmission electron microscope. From the area between the papillae sensory endings appearing in sections to be either single, double or triple are described.     

Antigenic affinity of species of the genus Diphyllobothrium (Cestoidea, Diphyllobothriidae) distributed in the territory of Karelia

Experiments on ringprecipitation reactions with homologous and heterologous antigenes of four species of diphyllobothriids have shown that D. dendriticum and D. ditremum are in a more close antigenic affinity. In relation to the above two species D. vogeli is approximately at the same level. D. latum displayed no antigenic affinity with the above species that, apparently, is connected with its parasitism only in mammals. Schemes of immunization of rabbits for obtaining antisera are given.     

Benthic algae support zooplankton growth during winter in a clear-water lake

We used stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ¹³C values of calanoid ( Eudiaptomus graciloides ) and cyclopoid ( Cyclops scutifer ) zooplankton in autumn suggest a food resource of pelagic origin during the ice-free period. The zooplankton δ¹³C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ¹³C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ¹³C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ¹⁵N of the C. scutifer food resource during winter was low compared to δ¹⁵N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via ¹⁵N-depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi-chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.     

The agglutination test of coracidia of pseudophyllidean cestodes and its use in cestodological research

Ability of coracidia to agglutination in homologous antiserum was established. The method of reaction of a direct agglutination of coracidia (RDAC) in the culture of alive larvae was described. When comparing the RDAC results in homologous and heterologous variants a dependence of the agglutination pattern on the degree of antiserum homology was established. On the example of RDAC of the cestodes Diphyllobothrium dendriticum and D. ditremum in polyvalent and species-specific antisera to D. dendriticum possibility was shown of RDAC usage in the studies on specific taxonomy of pseudophyllid cestodes.     

Ecological parasitology of polymorphic Arctic charr, Salvelinus alpinus (L.), in Thingvallavatn, Iceland

The helminth endoparasite fauna in four Arctic charr morphs, Salvelinus alpinus (L.), small benthivorous (SB), large benthivorous (LB), planktivorous (PL) and piscivorous (PI) charr, from Thingvallavatn, Iceland consisted of: Crepidostomum farionis (Trematoda: Allocreadiidae); Diplosttomum sp. (Trematoda: Diplostomatidae); Eubothrium salvelini; Diphyllobothrium dendriticum; D. ditremum (Cestoda: Pseudophyllidae); Proteocephalus longicollis (Cestoda: Proteocepha-lidae): and Philonema oncorhynchi (Nematoda: Filariidae). The morphs exhibited distinctive patterns in prevalences and parasite burdens (mean intensity and mean relative density of parasites). SB charr had high prevalence and parasite burden of the eye fluke Diplostomum sp. and none to very light infections of the other parasite species. LB charr had relatively high prevalence and parasite burden of the intestinal fluke C. farionis , whereas infections of the remaining parasite species were light to moderate. PL and PI charr had high prevalences and worm burdens of Diphyllobothrium spp. and P. longicollis . PL charr differed from PI charr in higher worm burden off P. longicollis and lighter burden of £. salvelini . Prevalences of P. oncorhynchi were high in PL and PI charr. Association of parasite intensities and age and length offish were investigated. The different infection patterns among the morphs agree well with their partitioning in food and habitat utilization, and confirm that there is a high degree of ecological segregation between the morphs. The results demonstrate the importance of ecological factors influencing transmission efficiency of parasites to the fish host.     

Isoenzymes of lactate dehydrogenase (EC 1.1.1.27) in Dicrocoelium dendriticum and Fasciola hepatica (Trematoda)

The isoenzymes of LDH (EC 1.1.1.27) were studied in Dicrocoelium dendriticum and Fasciola hepatica by horizontal electrophoresis on polyacrylamide gel. Six isoenzymes in D. dendriticum and four in F. hepatica were detected. Densitometric scans demonstrated that the enzyme pattern of LDH in D. dendriticum parasitizing hepatic tissue of Capra hircus was clearly different from the one obtained when the trematode parasitized other hosts such as Bos taurus or Ovis aries.     

The ecological interaction between arctic charr, Salvelinus alpinus (L.), and the plerocercoid stage of Diphyllobothrium ditremum

Six hundred and two arctic charr, Salvelinus alpinus , from a small lake (30 ha) were examined for infection with plerocercoids of Diphyllobothrium ditremum the only species of this genus present; 466 (77.4%) harboured the parasite in an overdispersed infection. The prevalence of infection increased with age and reached 100% at 7+ years for males and 8+ years for females. The rate of infection appeared to be related to the feeding biology of the charr which did not change within the age span studied. The rate of increase in density of infection (plerocercoids per fish) decreased with age as did the degree of overdispersion. It is concluded that the infection probably induces mortality in the fish population, and that such mortality is dependent on parasite density.     

The distribution of Poecilancistrium caryophyllum (Trypanorhyncha) plerocercoids in spot, Leiostomus xanthurus Lacèpéde, and spotted seatrout, Cynoscion nebulosus (Cuvier)

Spotted seatrout, Cynoscion nebulosus (Cuvier), and spot, Leiostomus xanthurus Lacèpéde, from two sites along Florida's west coast were collected, weighed, sexed and measured. A systematic search for plerocercoids of the cestode Poecilancistrium caryophyllum yielded infection prevalences of 81.9% for C. nebulosus and 25.0% for L. xanthurus . The maximum infection intensity was 10 (mean = 2.65) plerocercoids per fish in C. nebulosus and six (mean = 1.69) per fish in L. xanthurus . Significant correlations were found between infection prevalence and length in C. nebulosus , and a significant correlation was observed between intensity and length in both species. Condition coefficient ( K ) and intensity were negatively correlated in C. nebulosus but not in L. xanthurus . An iterative computer technique based on the truncated negative binomial distribution indicated no parasite-induced mortality occurred in either species. Sand drum, Umbrina coroides Cuvier, is reported as a new host record for P. caryophyllum .     

Abundance and distribution of Diphyllobothrium ditremum Creplin (Cestoda: Pseudophyllidea) plerocercoids in benthic whitefish, in northern Finnish Lapland

The prevalence of Diphyllobothrium ditremum plerocercoids in whitefish Coregonus lavaretus ranged between 70 and 100% in Lake Kilpisjärvi and in three other lakes in Northern Lapland, Finland. The mean abundance in Lake Kilpisjärvi (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 Kilpisjärvi; between March and April ( P <0·002) and between September and October ( P =0·042). In autumn the numbers of larvae increased particularly in female fish. The invasion rate of the parasite was lower in other lakes studied, and the infection rate in whitefish was closely related to the copepod food eaten.     

Comparison of surface topography of three species of Diphyllobothrium (Cestoda,pseudophyllidea) by scanning electron microscopy

Plerocercoids of different sizes as well as adult worms of D. dendriticum, D. latum and D. ditremum were studied using scanning electron microscopy (S.E.M.). In the plerocercoids there were found distinct differences in appearance and length of microtriches between these three species, while the microtriches of adult worms were more similar. A regional difference in microtrix appearance was found in the larvae of D. ditremum and D. dendriticum. This was not apparent with S.E.M. in adult worms. The length of ‘body’ microtriches in D. dendriticum varied with the length of the larvae. The topography of the genital atrium of mature and gravid proglottids in adult worms of these three species is also described.     

Parasites as indicators of individual feeding specialization in Arctic charr during winter in northern Norway

The relationship between infection with the food-transmitted parasites Diphyllobothrium dendriticum, D. ditremum (Cestoda) and Cystidicola farionis (Nematoda) and prey selection was studied in individual Arctic charr from Lake Takvatn, northern Norway. There was no correlation between parasites transmitted throughout prey organisms from benthic habitats (amphipods) and pelagic habitats (copepods). A strong relationship between infection with a parasite species and the corresponding intermediate host from the stomach content of individual charr, indicated an individual feeding specialization. Independent of size, charr specialized on the intermediate hosts of all three parasite species. Some charr maintained this specialization on specific prey items throughout the winter period. These parasite species are considered to be useful indicators of past prey selection.     

Cestode egg production dynamics and fertility in Diphyllobothrium dendriticum (Cestoda, Pseudophyllidea)

Dynamics of egg production of the tapeworm Diphyllobothrium dendriticum has been estimated experimentally in nestlings of the herring gull Larus argentatus per day and per reproductive period. The number of eggs in strobiles has been estimated for the maturation period. Mean egg production of the tapeworm per day (10.43 +/- 2.72 mln) is two orders of magnitude as high as the maximum number of eggs in a mature strobile (0.206 +/- 0.007). It is proposed to estimate coefficient of reproduction intensity as the ratio of egg output per unit of time and maximum egg number in a mature strobile.     

Composition and Structure of Zooplankton Communities in Eighteen Arctic and Subarctic Lakes

The factors influencing the composition and structure of zooplankton communities in 18 lakes in the Canadian arctic and subarctic were determined during 1975 and 1976. Phytoplankton were consumed in very low numbers by all species (Diaptomus sicilis, Heterocope septentrionalis, Cyclops scutifer, Daphnia longiremis, Bosmina longirostris, Holopedium gibberum, Keratella cochlearis, Kellicottia longispina) and therefore differences in algal productivity among the lakes had little effect on the zooplankton. Variations in surface area, maximum water depth, pH and the ionic composition of the water were also unimportant in controlling the communities. However, low temperature exerted strong influence over the diversity, abundance, fecundity and vertical distribution of most species.     

Molecular detection of Campylobacter spp. in California gull (Larus californicus) excreta

We examined the prevalence, quantity, and diversity of Campylobacter species in the excreta of 159 California gull (Larus californicus) samples using culture-, PCR-, and quantitative PCR (qPCR)-based detection assays. Campylobacter prevalence and abundance were relatively high in the gull excreta examined; however, C. jejuni and C. lari were detected in fewer than 2% of the isolates and DNA extracts from the fecal samples that tested positive. Moreover, molecular and sequencing data indicated that most L. californicus campylobacters were novel (<97% 16S rRNA gene sequence identity to known Campylobacter species) and not closely related to species commonly associated with human illness. Campylobacter estimates were positively related with those of fecal indicators, including a gull fecal marker based on the Catellicoccus marimammalium 16S rRNA gene.     

Residues of DDE and PCB in Eggs from Herring Gull (Larus Argentatus) and Common Gull (Larus Canus) in Norway

In 1969 294 eggs from herring gull were collected from eight different localities in Norway. The eggshell thicknesses were measured, and 10 eggs from each locality were analysed by gas liquid chromatography for organochlorine insecticides and polychlorinated biphenyls (PGB). Residues of DDE were demonstrated in all eggs, the concentrations varying from 0.2 to 5.4 p.p.m. in herring gull, and from 0.2 to 3.5 p.p.m. in common gull. DDT occurred only in four eggs from herring gull and then only in concentrations of from 0.1 to 0.3 p.p.m. Other organochlorine insecticides were not detected. Residues of PGB were found in all eggs from herring gull in concentrations of from 0.2 to 3.8 p.p.m. PGB 10, and in six out of nine eggs from common gull, from trace to 0.8 p.p.m. PGB 10. The analysed material showed a positive correlation between amounts present of DDE and of PGB. There was a significant difference between localities concerning the contents of DDE and PGB in eggs from herring gull. This variance may be taken into consideration by using the herring gull as an indicator organism, since this bird, especially in the northern part of Norway, is migratory. The residue concentrations of DDE and PGB were markedly higher in eggs from herring gull than in eggs from common gull. It is suggested that this may be related to the difference between these species in their feeding habits. The residues of organochlorines demonstrated in this investigation do not seem to have had any effect on eggshell thickness in herring gull.     

Food and growth of age-0 smelts, Osmerus eperlanus, in a Norwegian fjord lake

Pennate diatoms, especially Aslerionella spp. and Tabellaria fenestrata , were the most important food items for smelts in Lake Mjøsa during the first month of external feeding; rotifers and early stages of copepods were eaten occasionally. Later, during summer and autumn, crustacean zooplankton (cladocerans and copepods) were the most important food items; selected species were Polyphemus pediculus, Eudiaptomus gracilis, Limnocalanus macrurus, Heterocope appendiculata. Leplodora kindti , and Bythotrephes longimanus ; some smelts larger than 7.4 cm fed on Mysis relicta . In 1979 and 1980, mean lengths of smelts in October-November were 4.7 cm and 7.2 cm, respectively. A difference in length increment between the two years may have resulted from summer water temperatures being higher in 1980 than in 1979.     

Application of a bioenergetics model for analysis of growth and food consumption of subarctic whitefish Coregonus lavaretus (L.) in Lake Kilpisjärvi, Finnish Lapland

A bioenergetics model was used to estimate daily food consumption and growth of benthic whitefish Coregonus lavaretus (L.) of age groups 1+ to 10+, in oligotrophic Lake Kilpisjärvi, northern Finnish Lapland. Fish and zooplankton samples and water temperature data were collected twice per month from February to December 1993. Simulation results indicated wide seasonal variations in consumption and growth rates. Growth was in general slow; especially in age-group 6 the net increase in weight was slight. The fit of the model to the weight data was good, and the model was able to follow even rapid seasonal variations in the weight. There were clear changes in the diet during the year. In March, when the food intake was reduced, copepods, mainly adult calanoids, formed the bulk of the food consumed. The most intensive consumption period lasted from June to late September. Chironomid pupae and planktonic cladocerans were the major summer food items. The largest individuals fed mainly on molluscs during summer. Zooplankton survey and consumption estimates did not show directly that the population density of copepodids and adults of Eudiaptomus graciloides were affected by whitefish predation although their population density decreased in spring. Nauplii, showing the maximum population density in April, were not consumed. The role of copepod consumption in the timing of Diphyllobothrium ditremum plerocercoid transmission to whitefish was also discussed. The increased copepod consumption rate during winter results in high energy intake but also an increased risk of food transmitted parasite infection.     

Temperature effects on embryonic development and the life cycle of Diphyllobothrium dendriticum

Diphyllobothrium dendriticum eggs collected from hamster faeces were incubated at 10 or 20 degrees C, or maintained at 4 degrees C for 11-30 months. On day 65, 20-50% of eggs failed to hatch at 10 degrees C and 42-51% did not hatch by day 21 at 20 degrees C. Our study indicates that eggs begin to hatch in mid-August and persist until October in many lakes within the natural range of D. dendriticum. Our results demonstrate that eggs stored at 4 degrees C will hatch, suggesting they can persist in the environment for long periods and contribute to the D. dendriticum life cycle in high Arctic lakes by hatching months or years after release.