Macroparasite communities in European eels,Anguilla anguilla, from French Mediterranean lagoons, with special reference to the invasive speciesAnguillicola crassusandPseudodactylogyrusspp.

Abstract

European eel parasites, in particular invasive species, are suspected to play a role in the decline in the populations of their host. The aims of this work were to describe the parasitic fauna of eels in French Mediterranean lagoons and to study the epidemiological trends of the invasive helminth species, the nematode Anguillicola crassus and the monogenean Pseudodactylogyrus spp., in regard to spatio-temporal dynamics, host biological characteristics and parasite community. A total of 418 eels was sampled in eight lagoons between March 2003 and June 2005. Our results revealed a total macroparasite richness of 23 species: 1 Monogenea, 13 Digenea, 2 Cestoda, 3 Nematoda, 2 Acantocephala and 2 Crustacea. We found no variation in A. crassus abundance in Salses-Leucate lagoon in the same month across years. However, the nematode abundance was higher in eels caught in summer than in those caught in winter. Pseudodactylogyrus sp. was not found in Salses-Leucate lagoon, except in July 2004. Comparisons between the lagoons on the same date showed that they could be separated into two groups for both species' abundance: Grau-du-Roi, Mauguio, Palavas and Vaccarès lagoons, where abundance was rather high, against Bages-Sigean, Pierre-Blanche, Salses-Leucate and Thau lagoons, where abundance was rather low or nil. We found significant negative relationships between A. crassus abundance and the length and age of eels. We also found a significant positive relationship between A. crassus and Pseudodactylogyrus sp. abundance. Finally, our results showed significant positive relationships between both A. crassus and Pseudodactylogyrus sp. abundance and the abundance of the digeneans Prosorhynchus aculeatus and Lecithochirium gravidum. We discuss the results in regard to the dynamics of invasions, the characteristics of the parasite life cycles and the ecology of eels.

Silver European eels health in Mediterranean habitats

“…Fazio et al (2008) recorded higher prevalence in French Mediterranean lagoons, i.e., 67% in Salses lagoon and up to 94% in Mauguio lagoon in July 2004. In the present study, we found relatively low prevalence (ranging from 4% to 42%) depending on the site.…”

“…In the present study, we found relatively low prevalence (ranging from 4% to 42%) depending on the site. It is also possible that environmental conditions are not optimal for the life cycle of the parasite to complete in these sites (Fazio et al 2008). The sampling season may explain this difference with a maximal infection in summer when oxygen availability is low (Lefebvre et al 2002;Fazio et al 2008).…”

“…The complex life cycle of the eel makes this kind of research difficult, and only a few studies have attempted to measure effects of health quality on eel migration and reproduction success. It was also shown, both in naturally and experimentally infected eels, that this parasite has an effect on the silvering process (Fazio et al 2008(Fazio et al , 2012. Lefebvre et al (2002) suggested that eels with severely damaged swim bladders (Swim bladder Degenerative Index ≥ 4) would not be able to migrate and reproduce successfully.…”

Influence of host habitat on the occurrence of gill monogeneans Pseudodactylogyrus spp. on wild Japanese eels Anguilla japonica

“…N: sample size; TL: mean total length (± SD); P: prevalence; MI: mean intensity (± SD); MA: mean abundance (± SD); for type descriptions, see Conversely, the presence of P. kamegaii probably indicates the resource stability of non-catadromous individuals that primarily inhabit coastal and brackish-water areas. In European countries, Pseudodactylogyrus anguillae or unidentified species of Pseudodactylogyrus have sometimes been reported from European eels in brackish-water localities, with relatively high prevalence and intensity: for example, 2 fjords (salinity: 15 to 20 ‰ and about 10 ‰, respectively) adjoining the Baltic and North Seas and a strait (4 to 8 ‰) within the Baltic Sea, Denmark (Køie 1988); a lagoon (10 to 40 ‰) in the North Tyrrhenian Sea (Kennedy et al 1997) and 2 lagoons (15 to 35 ‰ and 30 to 42 ‰, respectively) in the North Adriatic Sea, Italy (Di Cave et al 2001); 3 lagoons (3 to 30 ‰, 8 to 36 ‰, and 8 to 30 ‰, respectively) in the Balearic Sea, Spain (Maillo et al 2005); lagoons (no salinity data) in the Gulf of Lion, Mediterranean Sea, France (Fazio et al 2008); and a lagoon, a fjord, and a strait (overall salinity range: 15 to 26 ‰) in northwestern Germany (Jakob et al 2008). However, it is noteworthy that P. anguillae was scarce on the Japanese eels inhabiting Misho Cove (3.6 to 30.7 ‰) in the present study, with a low intensity if present at all.…”

The European eel—the swim bladder–nematode system provides a new view of the invasion paradox

“…In theory, within-host parasite interactions are especially intense when species share the same niche (Pedersen and Fenton 2007), a fact that could explain the lack of exclusion between native macroparasites (that infest the digestive tract in the case of Cestoda and the gills in the case of Myxidium giardi) and the invasive Sbn (that occupies the sb). In fact, macroparasite communities in eels are typically characterised by their low densities, poor species diversity, high dominance and vacant niches (Kennedy and Guégan 1996;Fazio et al 2008). On the other hand, the fact that eels with high Sbn intensities had better body conditions (results not shown) suggests that, in eels with the most active feeding habits, there are better opportunities to predate intermediate or paratenic hosts.…”