Salinity dependence of parasite infestation in the European eel Anguilla anguilla in northern Germany

The aim of the study was to examine metazoan parasite communities of European eels (Anguilla anguilla) in fresh-water, brackish water and marine localities in northern Germany. In all, 29 parasite species/taxa were found in 170 eels: eight digeneans, one monogenean, five cestodes, ten nematodes, two acanthocephalans, and three crustaceans. Measures of diversity characteristics of the helminth communities included species richness, Shannon's diversity index and its evenness, and the Berger–Parker dominance index. The highest species diversity and lowest dominance values were calculated for the helminth communities of eels from the two Baltic Sea localities. Parasite communities of European eels clearly exhibit the habitat preferences of their hosts, salinity-dependent specificities, and a clustering into fresh-water, brackish, and marine groups. The highly pathogenic parasite species Anguillicola crassus and Pseudodactylogyrus spp. were found at all sampling sites in fresh water and brackish water, with high prevalence. Basic information is provided on the risks of restocking programmes solely focusing on fresh-water sites

The evolutionary ecology of complex lifecycle parasites: linking phenomena with mechanisms

Many parasitic infections, including those of humans, are caused by complex lifecycle parasites (CLPs): parasites that sequentially infect different hosts over the course of their lifecycle. CLPs come from a wide range of taxonomic groups-from single-celled bacteria to multicellular flatworms-yet share many common features in their life histories. Theory tells us when CLPs should be favoured by selection, but more empirical studies are required in order to quantify the costs and benefits of having a complex lifecycle, especially in parasites that facultatively vary their lifecycle complexity. In this article, we identify ecological conditions that favour CLPs over their simple lifecycle counterparts and highlight how a complex lifecycle can alter transmission rate and trade-offs between growth and reproduction. We show that CLPs participate in dynamic host-parasite coevolution, as more mobile hosts can fuel CLP adaptation to less mobile hosts. Then, we argue that a more general understanding of the evolutionary ecology of CLPs is essential for the development of effective frameworks to manage the many diseases they cause. More research is needed identifying the genetics of infection mechanisms used by CLPs, particularly into the role of gene duplication and neofunctionalisation in lifecycle evolution. We propose that testing for signatures of selection in infection genes will reveal much about how and when complex lifecycles evolved, and will help quantify complex patterns of coevolution between CLPs and their various hosts. Finally, we emphasise four key areas where new research approaches will provide fertile opportunities to advance this field

Annelid symbiont assemblage and European stone crayfish − a deterministic relationship with implications for conservation management

The protected European stone crayfish, Austropotamobius torrentium, is a host to epibionts inhabiting its exoskeleton. Despite evidence of the close association of these epibionts to the crayfish and the beneficial services provided for the crayfish, the main factors influencing their occurrence, distribution and abundance are still poorly understood. In order to investigate the stone crayfish epibiont community, the ecological requirements of individual species, and aspects of the host-epibiont relationship we collected data at several crayfish populations in Austria, Switzerland and Germany. At each location, we recorded the epibiont position on the crayfish host along with a number of biotic and abiotic parameters. Apart from recording the Branchiobdella species B. parasita, B. hexadonta, B. pentadonta and B. balcanica, we detected for the first time the polychaete Hystricosoma chappuisi in the European Alps. Species-specific biogeographical and habitat factors such as river catchment borders, crayfish length, water temperature and nutrients concentration were identified to be important for the occurrence and abundance of epibionts. Branchiobdella species were strongly linked to certain host body areas, providing evidence for the existence of different functional traits within the annelid assemblage. With this study we demonstrate that the crayfish–epibionts relationship includes structural and functional complexities that can be important for defining management units in future conservation policies. Due to benefits for the mutualistic relationship, restocking and reintroduction actions are likely to be more successful, if ecological requirements of both the host and the epibiont species are considered

Massovaja invazija metacerkarijj Bucephalus polymorphus Baer 1827, v glazu leshha - Abramis brama (L.)

The mass incidence of the parasite was detected in Abramis brama (L) from the dam reservoir of the Gródek-Żur electricity works on the Wda river (Bydgoszcz voivodeship). Seven breams weighing 530-1530 g, measuring 29/35-41/49 cm in lenght (longitudo corporis, longitudo totalis). In all fishes there was a strong protrusion of the cornea that showed small white spots, visible with naked eye (Phot. 1). Post-mortem examinations revealed considerable enlargement of the anterior chamber of the eye with small amount of the vitreus and sticky, hazy fluid in the bulbus. The cornea contained numerous metacercariae (Phot. 2); a mass incidence of the latter was also found under the skin, on the head, anterior part of the body, on pectoral fins and on gills. The most charactcristic changes appeared in the cornea, where metacercariae were present in extremely high numbers; they were either single and disseminated of formed large accumulations. Occasionally, the cornea showed canals burrowed by migrating larvae prior to incystation (Phot. 3). On the transversal sections of the cornea there are holes containing encysted metacercariae; laceration of the corneal surface and separation of the tissue layers are visible (Phot. 4). At autopsy, the cornea was friable, which could be seen distinctly from the presence of transversal fissures in the microtome sections (Phot. 5)