Dynamics and predicted decline of Anguillicola crassus infection in European eels, Anguilla anguilla, in Neusiedler See, Austria.

The eel population in Neusiedler See has been maintained by regular massive stocking since 1958. After the establishment of the National Park Neusiedler See-Seewinkel in 1993, eel stocking was prohibited and the population, together with the specific parasites of eels, was predicted to decline to extinction within 10 years. This investigation was undertaken to document the decline and extinction of the Anguillicola crassus population in eels. From 1994 to 2001, 720 eels were collected from two sites in the lake. Prevalence and abundance of A. crassus were lower in spring than in summer and autumn and larger eels harboured more parasites than smaller ones. Neither year of study nor sampling site were correlated with parasite infection levels. No significant trend in the population parameters of A. crassus was detected over the 8 years of the survey. This suggested that there had been no significant decline in the eel population. This suggestion was confirmed by investigations of the fishery, which also found evidence of regular illegal stocking. The stability of the A. crassus population over the past decade seems to reflect the lack of change in eel population density. No mass mortalities of eels occurred over the period despite the many similarities between Neusiedler See and Lake Balaton in Hungary. Differences in eel size, eel diet and the lack of large-scale insecticide use are discussed as possible explanations for the absence of eel mass mortalities in Neusiedler See.

Ligula intestinalis infection as a potential source of bias in the bioindication of endocrine disruption in the European chub Leuciscus cephalus.

European chub Leuciscus cephalus collected from five localities in the lowland and subalpine regions of Austria were analysed for oestrogenic effects of endocrine-disrupting chemicals and the presence of the plerocercoid of the tapeworm Ligula intestinalis. Of 1494 chub analysed, only seven (six males, one female) were found to be infected with single, but large plerocercoids up to 15 cm in length. Ligula-infected fish showed comparatively immature gonads, as demonstrated by the gonadosomatic index and gamete developmental stages. Plasma levels of the egg precursor protein vitellogenin also showed concentrations ranging below the detection limit. The present results indicate that chub infected with L. intestinalis and exposed to exogenous oestrogenic compounds can result in reduced gonadal maturation and produce false oestrogen-positive diagnoses in male fish. For plasma vitellogenin levels, L. intestinalis infections can result in false oestrogen-negative diagnoses in male and female fish.

Long-term investigation of the composition and richness of intestinal helminth communities in the stocked population of eel, Anguilla anguilla, in Neusiedler See, Austria.

Data from a long-term study of the intestinal helminth parasite community of eels, Anguilla anguilla, stocked into the shallow eutrophic Neusiedler See, Austria, were collected over an 8 year period (1994-2001). In total, 720 eels from 2 sampling sites were examined. The parasite community showed characteristics similar to those in the natural eel populations in rivers of the UK and mainland Europe: it was species poor, with only 5 species (Acanthocephalus lucii, Acanthocephalus anguillae, Raphidascaris acus, Proteocephalus macrocephalus, Bothriocephalus claviceps) comprising the component community and a maximum infracommunity richness of 4 species. Over the period, the intestinal parasite community of the sampling site in Illmitz, which was originally dominated by A. lucii, changed. As levels of A. anguillae increased to a point at which it dominated the community, diversity increased whilst dominance of a single species decreased. By contrast the community in the southern sampling site remained rather constant with a continuous high infection level of A. anguillae and low abundance of A. lucii. Both acanthocephalan species exhibited higher infection levels in larger eels and in different seasons of the year and the infection parameters were significantly different between the years of study. The significant differences in the infection levels of the 2 acanthocephalan species at the 2 sampling sites were surprising as both acanthocephalan species use the same intermediate host, Asellus aquaticus, and the sampling sites were in close proximity and were similar in terms of water quality, host size and invertebrate abundance. Differences in the fish communities of the 2 sampling sites and eel movements rather than interspecific competition are discussed as possible explanations for the differences in the parasite communities of the 2 sampling sites.

Surface carbohydrates of Eudiplozoon nipponicum pre- and post-fusion.

The development of the monogenean Diplozoon (Nordmann, 1832) (Diplozoidae) necessitates fusion of two larval stages (diporpae) into one double organism. How diporpae find, distinguish and contact each other is unclear, nor is the nature of the stimuli responsible for the dedifferentiation of cells and the formation of new tissues at the site of somatic fusion. Previous studies have implied a role for carbohydrates and glycoproteins in the interactions between helminth parasites and their hosts. Hypothetically, glycoconjugates may also be involved in the establishment of parasite-parasite associations. Changes in the surface saccharide residues during the development of Eudiplozoon nipponicum, a gill ectoparasite of carp (Cyprinus carpio) are described. Flat-fixed specimens and sections of diporpae, juveniles (just-fused) and adult worms were examined following exposure to a panel of 12 FITC-conjugated lectins. All developmental stages exhibited a specific surface binding pattern with ten lectins, indicating that Man/Glc, GlcNAc, Gal and GalNAc are probably present on their surfaces. No reaction was observed with Fuc-specific lectins (UEA-I and LTA). There is evidence that parasite development is accompanied by both qualitative and quantitative changes in the saccharide pattern distribution. The diporpa sucker reacted with nine lectins, excluding BS-II. A very strong binding of PNA, LCA and ConA (Gal and Man/Glc-specific lectins) was observed with the papilla glands of juvenile worms. The role of glandular secretions in this unique fusion process is discussed.

Endoparasitic helminths of the European eel, Anguilla anguilla, from four disconnected meanders from the rivers Leie and Scheldt in western Flanders, Belgium.

The endoparasitic helminth communities of the European eel, Anguilla anguilla (L.), were investigated in four meanders, cut off from the rivers Leie and Scheldt in western Flanders, Belgium. Six species of helminths (2 cestodes, 2 nematodes and 2 acanthocephalans) were found. The dominant parasite species was the nematode Anguillicola crassus (Kuwahara, Niimi et Itagaki, 1974) infecting 79% of the eel population with intensities up to 112 specimens per fish. At two localities no acanthocephalans could be found, whereas these parasites were very common at the other sites. The prevalence, mean intensity, intensity and abundance, their correlation to the body length, and the frequency distributions were analysed. The site selection of parasites is in relation to food composition and feeding habits of eels, physiological and structural differences in the intestine and possible interspecific competition were discussed.