Morphometric analysis of four species of Eubothrium (Cestoda: Pseudophyllidea) parasites of salmonid fish: an interspecific and intraspecific comparison

Four species of the genus Eubothrium (E. crassum, E. fragile, E. rugosum and E. salvelini) were subjected to morphometric comparison. Discriminant analysis was conducted utilising 17 characters measured on the scolex and strobila of 101 specimens. Univariate statistics were first used to detect features that were useful for separating individual Eubothrium species and two different host populations of E. salvelini. Subsequent multivariate discriminant analysis, combining all the measured variables, made it possible to separate all four species. A comparison of the four taxa revealed that (1) E. fragile is the most distinct species, possessing a much smaller scolex than the other congeners, and its similarity with the other marine species E. crassum is not proven; (2) the two freshwater taxa, E. rugosum and E. salvelini are the most similar; (3) the characters most suitable for species differentiation are the length of the scolex, the width of the apical disc, the width of the neck and its area, the width of eggs and the number of testes; (4) the width of the apical disc was confirmed to be the most stable character at the intraspecific level (within E. salvelini host populations) and is therefore considered to be a trait of the highest discriminative power in the subset of four Eubothrium species.     

Studies on the biology of Eubothrium salvelini and E. crassum in resident and migratory Salvelinus alpinus and Salmo trutta and in S. salar in North Norway and the islands of Spitsbergen and Jan Mayen

Samples of Eubothrium salvelini and E. crassum were obtained from resident and migratory Salvelinus alpinus and Salmo trutta and from S. salar at sea from North Norway and the islands of Spitsbergen and Jan Mayen. Scolex dimensions proved an unsuitable character for identifying these two parasite species, and use of alternative characters confirmed that E. salvelini is specific to Salvelinus and E. crassum to Salmo. Distributions of both species are co-extensive with their hosts, but levels of infection in any locality relate to the abundance of zooplankton. E. salvelini exhibits seasonal maturation and incidence cycles in char. It is recognised as being a freshwater parasite, although some individuals can survive the period of marine migration of sea char. Returning migrant char may contain such individuals together with small plerocerciform parasites acquired almost immediately upon their re-entry to freshwater. No evidence for marine infections with E. salvelini was found. The presence of plerocerciform and gravid adult E. crassum in salmon caught at sea confirms the existence of a marine life cycle and a marine race in this species. In salmon moving from one medium to the other the marine and freshwater races replace each other, but in sea trout, which spend shorter periods at sea, complete replacement may not occur and at any one time fish may harbour individuals of both races. Recognition of the existence of two races clarifies much of the confusion surrounding the biology of this species.     

Host specificity and geographical distribution of Eubothrium in European salmonid fish

The host specificity and distribution of Eubothrium crassum (Bloch, 1779) and Eubothrium salvelini (Schrank, 1790), morphologically fairly similar pseudophyllidean tapeworms parasitizing salmonid fish, were critically assessed on the basis of morphological and genetic evaluation of extensive material collected from different definitive hosts and geographical regions in Europe. Eubothrium crassum occurs in fish of the genera Salmo, i.e. salmon (S. salar - both freshwater and marine), sea trout (S. trutta trutta), brown trout (S. trutta fario), and lake trout (S. trutta lacustris), and also in Danubian salmon (Hucho hucho) and vendace (Coregonus albula). Eubothrium salvelini parasitizes Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) in Europe, and also whitefish (Coregonus wartmanni). Rainbow trout (Oncorhynchus mykiss), which is not a native European fish species, was found to be a suitable definitive host for both Eubothrium species, which may occur simultaneously in the same fish. Previous records of E. crassum in Arctic char and brook trout, and those of E. salvelini in fish of the genus Salmo were most probably misidentifications. Most studies of Eubothrium have involved salmonids from the northern part of Europe, with few records from southern and south-eastern Europe. This study also confirmed the reliability of the morphology of the apical disc for the discrimination of E. crassum and E. salvelini.     

A comparison of the internal transcribed spacer of the ribosomal DNA for Eubothrium crassum and Eubothrium salvelini (Cestoda: Pseudophyllidea), parasites of salmonid fish

The internal transcribed spacers (ITS-1 and ITS-2) and 5.8S subunit of the ribosomal RNA gene of Eubothrium crassum and Eubothrium salvelini, cestode parasites of salmonid fish, were sequenced and compared. The lengths and GC contents of the regions sequenced were 1119 bp and 50.1% for E. crassum, and 1117 bp and 50.5% for E. salvelini, respectively. Sequence alignment and comparison of both taxa showed 97.9% similarity. Within the ITS-1 and ITS-2 of both species, the restriction enzymes MspI and Bsh1236I possessed different cleavage sites and could be employed for rapid differentiation of both species of Eubothrium by PCR-RFLP.     

The occurrence of Eubothrium fragile (Cestoda: Pseudophyllidae) in twaite shad, Alosa fallax (Lacépède) in the River Severn

The occurrence, size and maturity changes of Eubothrium fragile have been studied in postlarvae, juveniles and adult twaìte shad, Alosa fallax , from several locations in the River Severn. Parasites were only found in adult shad and not in post-larvae or juveniles. No juvenile or recently acquired cestodes were identified as such, but adults were present in shad throughout the whole period of their spawning migration. A large proportion of the parasites were gravid upon arrival in the river and, although eggs were subsequently released into fresh water, there was no loss of cestodes from the fish. It was concluded that E. fragile is a marine species, that the parasites found in adult shad in fresh water were the residue of a marine life cycle and that the eggs released in fresh water were part of the parasite's natural reproductive wastage. The distribution and biology of E. fragile were discussed and it is considered that it is typical of the marine species of the genus.     

Fractionation of δ15N and δ13C for Atlantic salmon and its intestinal cestode Eubothrium crassum

Stable isotopes of nitrogen (δ¹⁵N) and carbon (δ¹³C) were measured for Atlantic salmon Salmo salar and their intestinal cestode, Eubothrium crassum , sharing the same diet. Atlantic salmon muscle tissues were enriched in ¹⁵N and depleted in ¹³C compared to their prey (sprat Sprattus sprattus sprattus ) and their intestinal cestode. There was no significant difference in δ¹⁵N or δ¹³C between E. crassum and the sprat. Differences in nutrient uptake and intestine physiology between Atlantic salmon and E. crassum are discussed, as well as how these may give rise to different fractionations of stable isotopes between a host and its parasites. Furthermore, Atlantic salmon contained a significantly higher lipid content than their prey, which may partly explain differences in δ¹³C values between the host and its cestode. In addition, cestodes inhabiting lipid-rich hosts were also lipid rich. Larger Atlantic salmon were enriched in ¹⁵N compared to smaller fish. Cestodes inhabiting large hosts were also enriched in ¹⁵N compared to parasites living in smaller hosts. The last two results were explained by larger fish possibly feeding from a higher trophic level, or from larger and older prey, that resulted in both a higher lipid content and an enrichment in ¹⁵N.     

Metazoan parasite community structure of sea trout on the west coast of Ireland

A total of 129 sea trout smolts from 10 locations on the west coast of Ireland were examined for metazoan parasites. Of 11 species identified only four had a prevalence >20%. Two species Hysterothylacium aduncum and Hemiuris communis have a confirmed marine origin; Eubothrium crassum has been shown to exist in both the sea and fresh water. The remaining species were fresh water. Overall the parasite community was dominated by autogenic species with only Diphyllobothrium dendriticum having allogenic transmission. Infracommunity values for mean species richness, and Brillouins index of diversity were low, indicating the presence of an impoverished helminth community with little potential for interspecific interaction. The relationship between marine helminths and sea lice was also examined.     

Electron microscope investigation of bacteria associated with the tegument of the tapeworm species Eubothrium rugosum, a parasite of the intestine of burbot

Bacteria associated with the tegument of the tapeworm species Eubothrium rugosum (Cestoda, Pseudophyllidea) parasitizing the intestine of burbot (Lota lota) were studied using transmission and scanning electron microscopy. Three morphological types of the bacteria were revealed. Bacteria of the first type are localized between microtrichia and fit to them closely. Bacteria of the second (gram-positive) and third (gram-negative) types are localized over microtrichia of the tegument and do not attach to the surface. Physiological functions of the bacteria are discussed.     

Parasites of arctic charr Salvelinus alpinus (Linnaeus) and their use in separating sea-run and non-migrating charr

Metazoan parasites of arctic charr, Salvelinus alpinus , from the Nettilling Lake–Koukdjuak River system, Baffin Island, were studied. Non-migrating charr hosted 9 species of parasites while sea-run charr hosted 15 species of parasites. Diphyllobothrium spp., Eubothrium salvelini , and Proteocephalus longicollis were found to be good indicators of non-migrating charr and Brachyphallus crenatus, Bothrimonus sturionis and Prosorhynchus squamatus were good indicators of sea-run charr. Using these parasites as biological tags, the proportion of charr caught by the commercial fishery at the outlet of the Koukdjuak River were determined to be approximately 80% sea-run and 20% non-migrating charr. Step-wise discriminant statistical analysis on morphic characters of charr, designated as sea-run and non-migrating by their parasites, showed these charr to differ morphologically.     

Ecological and evolutionary significance of resting eggs in marine copepods: past, present, and future studies

The occurrence of a resting egg phase in the life cycle of marine and freshwater planktonic copepods is well documented and receiving increasing attention by investigators. The species generally occur in coastal marine waters, freshwater ponds and lakes in areas that undergo strong seasonal fluctuations, though examples have been reported for tropical and sub-tropical areas not subject to such extreme fluctuations. Typically such species disappear from the water column for portions of the year, but remain in the region as benthic resting eggs. Studies to date have focused on the conditions that promote the occurrence of resting eggs, the factors that affect their survival and hatching from sediments, the existence of egg banks in sediments, and the impact of resting eggs on plankton community structure. Benthic resting eggs of copepods include diapause eggs as well as subitaneous (non-diapause) eggs that are quiescent due to conditions in the sediments. As with other groups of organisms the resting egg phase is viewed as being critical for the perpetuation of species year after year, especially those that disappear from the water column for portions of the year. Some data indicate that eggs can survive for many years in sediments which would expand their influence to evolutionary time scales. This paper summarizes our understanding of embryonic dormancy in marine copepods.     

Systematics of the Genus Eubothrium Nybelin (Cestoda, Pseudophyllidea), with Partial Re-description of the Species

Material from as many species of the cestode genus Eubothrium as could be obtained (six out of nine existing species), from a range of hosts and from both marine and freshwater habitats, were examined both by light and scanning electron microscopy. The scolex shape as seen with SEM turned out to be a very valuable specific character. Particular attention was also paid to the possibility that intra-specific races, distinguishable on biological criteria, might in addition exhibit characteristic morphological differences.     

Assessing invasion risk across taxa and habitats: life stage as a determinant of invasion success

Aim Many aquatic invertebrates produce dormant life‐history stages as a means to endure inhospitable environments and to facilitate natural long‐distance dispersal, yet we have little understanding of the role of dormant stages as a mechanism for human‐mediated introductions of non‐indigenous species. We explore the survival of invertebrate dormant eggs in collected ships’ ballast sediment over a 1‐year period to determine relative invasion potential across taxa (i.e. rotifers, copepods, cladocerans and bryozoans) and different habitats (freshwater, marine). Location Canadian Atlantic and Pacific coasts and Laurentian Great Lakes. Methods During 2007 and 2008, 19 ballast samples were collected as a part of a larger study. The degradation rate of dormant eggs was assessed by enumerating dormant eggs and by conducting viability hatching experiments. Results Taxa examined included rotifers, copepods, anomopods, onychopods and bryozoans. Dormant eggs of rotifers degraded at the highest rate of all taxa examined, with no viable eggs remaining within 10 months. Copepods showed a less rapid degradation rate than rotifers. The degradation rate of anomopod dormant eggs was significantly slower than that of both rotifers and copepods. Onychopods and bryozoans did not visibly degrade at all over 12 months. Viability hatching experiments were successful for rotifers, copepods, and anomopods. Onychopods and bryozoans did not hatch during any of the three hatching trials. Main conclusions Dormancy is not equally beneficial to all invertebrate taxa. Our results indicate that dormant eggs of rotifers and copepods degrade at a rapid rate and may not pose high invasion risk. In contrast, the slow degradation rate of anomopod dormant eggs and the lack of degradation of onychopod and bryozoan dormant eggs could result in high invasion risk because of their accumulation in ballast tanks. Species having resistant dormant eggs mostly belong to freshwater taxa making freshwater habitats at higher invasion risk by dormant invertebrates than marine habitats.     

A Comparative Study of Eubothrium Salvelini and E. crassum (Cestoda: Pseudophyllidea) Parasites of Arctic Charr and Brown Trout in Alpine Lakes

We compared the morphology, morphometry, and some aspects of the biology and ecology of Eubothrium crassum and E. salvelini, two pseudophyllidean tapeworms in brown trout, Salmo trutta m. lacustris, and Arctic charr, Salvelinus alpinus, in lakes of the western part of the Alps. The taxonomic importance of the apical disc for the discrimination of both taxa was confirmed. The apical disc of E. crassum is rectangular, possessing two deep grooves above the bothriae and 2–16 additional indentations. In E. salvelini, the apical disc is bilobed and bilaterally symmetric. We found new and significant interspecific differences in the length and width of the scolex, the diameter of the apical disc, and the width of the neck, with all measurements being larger in E. crassum. The two species differ in the number and size of the testes (fewer and larger in E. salvelini), the length of the cirrus sac (longer in E. crassum), and the size of vitelline follicles (larger in E. salvelini). Vitelline follicles of E. crassum are always cortical and sometimes enter into the outermost muscle fibres, whereas follicles of E. salvelini are situated largely medullary with few follicles entering between the innermost bundles of muscles. The eggs and the oncospheres of E. salvelini are larger. The embryonic hooks of E. crassum measure 14–18 m whilst those of E. salvelini are 18–26 m. For both taxa, the intraspecific variability in morphometric characters was fairly low. The prevalence and intensity of infection of E. crassum and E. salvelini in their respective fish hosts were very high (prevalence 90–94% mean intensity 36.3 and 6.6, maximums of 172 and 63 tapeworms per fish, respectively). E. salvelini eggs were spontaneously released throughout the year except for winter months; E. crassum laid eggs only in summer (June–August). Natural infection of copepods with Eubothrium procercoids was very low (prevalence 0.002%). The morphogenesis of Eubothrium procercoids was studied in an intermediate host, the copepod Cyclops prealpinus, that had been simultaneously infected with both species.     

The karyotype of Eubothrium rugosum (Cestoda: Pseudophyllidea)

The diploid chromosome set of Eubothrium rugosum contains 16 elements. The karyotype consists of three pairs of metacentric, three pairs of acrocentric and two pairs of submeta-metacentric chromosomes. Their mean absolute length ranges from 2.20 to 8.80 microns. The first two pairs of large metacentric chromosomes comprise over 45% of the total complement length.     

SYSTEMATIC EVALUATION OF THE GENUS HILDENBRANDIA (RHODOPHYTA): A SYNTHESIS OF TECHNIQUES

The evolutionary relationships among members of the red algal genus Hildenbrandia have not been well understood for several reasons. For example, the genus contains both marine and freshwater representatives, all of which are non-calcified and crustose, and few have definitive morphological characters for classification. Hildenbrandia is also assumed to be completely asexual (reproduction by tetrasporangia in marine forms and by gemmae in freshwater populations), and characters of the female gametangial system and post-fertilization structures are not available for comparative studies. Currently there are 14 marine and five freshwater species and infraspecific taxa recognized within the genus. We used phylogenetic analyses (parsimony, distance and maximum likelihood) of DNA sequences of commonly employed genes ( rbc L and 18S rRNA) to examine the evolutionary relationships among representatives of many of these taxa. In addition, we employed morphometrics (principal co-ordinates and cluster analyses) of several measured characters of these same representatives, as well as all available type specimens, to determine the number of morphologically-delimited entities within the genus. Thus far our results indicate that some characters traditionally used to distinguish species of Hildenbrandia , such as tetrasporangial division pattern, may not be useful in some cases, and a revision of the taxonomy of the genus will be necessary. Although the marine and freshwater species of Hildenbrandia appear to be well separated in our molecular analyses of European specimens, this trend was not observed for North American specimens. High sequence divergence values were calculated for both the rbc L and 18S rRNA genes of Hildenbrandia , compared to other red algal genera.     

Eubothrium crassum in migratory trout, Salmo trutta L., in the sea

The incidence and intensity of infection of various ages and conditions of migratory trout by Eubothrium crassum are described. A marine source of the worm seems likely and explanations for the characteristics of the parasite burden are given on this assumption. Within weeks of first going to sea the hosts accumulate large numbers of the parasite. One year suffices for the life cycle of Eubothrium but growth continues for at least two years and possibly for longer. The parasite burden decreases in older fish because of the stress imposed on the parasite by successive migrations of the host to and from fresh water and because older fish tend to feed earlier in the year.     

Helminths in an intensively stocked population of lake trout, Salvelinus namaycush, from Lake Huron

Eighty stocked lake trout Salvelinus namaycush (Salmonidae), collected from 2 locations in Lake Huron in May 1995, were examined for parasites. The parasite fauna of this top predator in Lake Huron was characterized by only 6 helminth species. Echinorhynchus salmonis infected all lake trout with a mean intensity of 163.9. The intensity of this acanthocephalan species significantly increased with host length and weight. Eubothrium salvelini infected 78 lake trout with a maximum number of 81 scoleces counted. Diplostomum sp., Cyathocephalus truncatus, Capillaria salvelini, and Neoechinorhynchus sp. infrequently infected lake trout. The low parasite species richness in these lake trout is believed to be due to their large size at stocking and to the loss of historical enzootic host-parasite relationships that followed the absence of this fish species in Lake Huron for 26 yr.     

Effects of an adaptive zone shift on morphological and ecological diversification in terapontid fishes

A fundamental goal of evolutionary ecology is understanding the processes responsible for contemporary patterns of morphological diversity and species richness. Transitions across the marine–freshwater interface are regarded as key triggers for adaptive radiation of many clades. Using the Australian terapontid fish family as a model system we employed phylogenetic analyses to compare the rates of ecological (dietary) and morphological evolution between marine and freshwater species of the family. Results suggested significantly higher rates of phenotypic evolution in key dietary and morphological characters in freshwater species compared to marine counterparts. Moreover, there was significant correlation between several of these dietary and morphological characters, suggesting an underlying ecomorphological aspect to these greater rates of phenotypic evolution in freshwater clades. Australia’s biogeographic history, which has precluded colonisation by many of the major ostariophysan fish families that make up much global freshwater fish diversity, appears to have provided the requisite ‘ecological opportunity’ to facilitate the radiation of invading marine-derived fish clades.     

Diversity of the free-living marine and freshwater Copepoda (Crustacea) in Costa Rica: a review

The studies on marine copepods of Costa Rica started in the 1990’s and focused on the largest coastal-estuarine systems in the country, particularly along the Pacific coast. Diversity is widely variable among these systems: 40 species have been recorded in the Culebra Bay influenced by upwelling, northern Pacific coast, only 12 in the Gulf of Nicoya estuarine system, and 38 in Golfo Dulce, an anoxic basin in the southern Pacific coast of the country. Freshwater environments of Costa Rica are known to harbor a moderate diversity of continental copepods (25 species), which includes 6 calanoids, 17 cyclopoids and only two harpacticoids. Of the +100 freshwater species recorded in Central America, six are known only from Costa Rica, and one appears to be endemic to this country. The freshwater copepod fauna of Costa Rica is clearly the best known in Central America. Overall, six of the 10 orders of Copepoda are reported from Costa Rica. A previous summary by 2001 of the free-living copepod diversity in the country included 80 marine species (67 pelagic, 13 benthic). By 2009, the number of marine species increased to 209: 164 from the Pacific (49% of the copepod fauna from the Eastern Tropical Pacific) and 45 from the Caribbean coast (8% of species known from the Caribbean Basin). Both the Caribbean and Pacific species lists are growing. Additional collections of copepods at Cocos Island, an oceanic island 530 km away of the Pacific coast, have revealed many new records, including five new marine species from Costa Rica. Currently, the known diversity of marine copepods of Costa Rica is still in development and represents up to 52.6% of the total marine microcrustaceans recorded in the country. Future sampling and taxonomic efforts in the marine habitats should emphasize oceanic environments including deep waters but also littoral communities. Several Costa Rican records of freshwater copepods are likely to represent undescribed species. Also, the biogeographic relevance of the inland copepod fauna of Costa Rica requires more detailed surveys.