scholarly journals Elemental composition of otoliths as a discriminator of life stage and growth habitat of the European eel, Anguilla anguilla

2005 ◽  
Vol 56 (5) ◽  
pp. 629 ◽  
Author(s):  
W. N. Tzeng ◽  
K. P. Severin ◽  
C. H. Wang ◽  
H. Wickström
Keyword(s):  
Elemental Composition ◽  
Environmental History ◽  
Life Stage ◽  
Anguilla Anguilla ◽  
Primary Component ◽  
European Eel ◽  
Yellow Eel ◽  
Minor Elements ◽  
Electron Probe Microanalyser ◽  
History Of

The hypothesis that elemental composition of otoliths of the eel (Anguilla spp.) changes with life stage and growth habitat was tested in the present study. The minor elements Cl, Na, K, Mg, Ca, Sr and P in otoliths of European eels (Anguilla anguilla) were examined by using an Electron Probe Microanalyser (EPMA) equipped with wavelength dispersive spectrometers (Cameca SX-50). Yellow-stage eels were collected from coastal waters and lakes of Sweden in 1987, 1988, 1991, and 1994, with ages ranging from 5 to 18 years old. Strontium maps and profiles of Sr : Ca ratio, as well as the elver check in otoliths, were used to classify life history stages of the eels as leptocephalus, and freshwater- and seawater-resident yellow eels. Canonical score plots of the otolith elemental compositions of the freshwater-resident yellow eel were completely separated from those of leptocephalus and seawater-resident yellow eel, but the latter two partially overlapped. Strontium is the primary component in determining the discrimination, but the nutrient-related (S and P), and the physiologically controlled elements (Na and Cl), may also play an important role in the discrimination. These results indicate that multiple-elemental information can provide additional insight into the migratory environmental history of diadromous fishes.

The life cycle of Paraquimperia tenerrima: a parasite of the European eel Anguilla anguilla

2005 ◽  
Vol 79 (2) ◽  
pp. 169-176 ◽  
Author(s):  
J.A. Shears ◽  
C.R. Kennedy
Keyword(s):  
Life Cycle ◽  
Intermediate Host ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Temperature Dependent ◽  
Free Living ◽  
Freshwater Invertebrate ◽  
Third Stage ◽  
History Of ◽  
Whole Life Cycle

AbstractPrevious studies on the life history of the nematode eel specialist Paraquimperia tenerrima (Nematoda: Quimperiidae) have failed to determine whether an intermediate host is required in the life cycle. In the laboratory, eggs failed to hatch below 10°C, hatching occurring only at temperatures between 11 and 30°C. Survival of the free-living second stage larvae (L2) was also temperature dependent, with maximal survival between 10 and 20°C. Total survival of the free-living stages (eggs and L2) is unlikely to exceed a month at normal summer water temperatures, confirming that parasite could not survive the 6 month gap between shedding of eggs in spring and infection of eels in early winter outside of a host. Eels could not be infected directly with L2, nor could a range of common freshwater invertebrate species. Third stage larvae (L3) resembling P. tenerrima were found frequently and abundantly in the swimbladder of minnows Phoxinus phoxinus from several localities throughout the year and were able to survive in this host in the laboratory for at least 6 months. Third stage larvae identical to these larvae were recovered from minnows experimentally fed L2 of P. tenerrima, and eels infected experimentally with naturally and experimentally infected minnows were found to harbour fourth stage larvae (L4) and juvenile P. tenerrima in their intestines. Finally, the whole life cycle from eggs to adult was completed in the laboratory, confirming that minnows are an obligate intermediate host for P. tenerrima.

scholarly journals Is the continental life of the European eel Anguilla anguilla affected by the parasitic invader Anguillicoloides crassus ?

2013 ◽  
Vol 280 (1754) ◽  
pp. 20122916 ◽  
Author(s):  
François Lefebvre ◽  
Géraldine Fazio ◽  
Béatrice Mounaix ◽  
Alain J. Crivelli
Keyword(s):  
Reproductive Potential ◽  
Adaptive Immune Response ◽  
Anguilla Anguilla ◽  
Individual Variability ◽  
Growth Potential ◽  
Size Increase ◽  
European Eel ◽  
History Of ◽  
Internal Marker ◽  
Anguillicoloides Crassus

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus , high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (+11% and +41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host–parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected—via trophic parasite transmission—during their continental life.

scholarly journals Rethinking swimming performance tests for bottom-dwelling fish: the case of European glass eel (Anguilla anguilla)

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
P. Vezza ◽  
F. Libardoni ◽  
C. Manes ◽  
T. Tsuzaki ◽  
W. Bertoldi ◽  
...  
Keyword(s):  
Water Temperature ◽  
Swimming Performance ◽  
Life Stage ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Fish Swimming ◽  
Glass Eel ◽  
Swimming Time ◽  
Swimming Mode ◽  
Active Swimming

Abstract Systematic experiments on European eel (Anguilla anguilla) in their juvenile, early life stage (glass eel), were conducted to provide new insights on the fish swimming performance and propose a framework of analysis to design swimming-performance experiments for bottom-dwelling fish. In particular, we coupled experimental and computational fluid dynamics techniques to: (i) accommodate glass eel burst-and-coast swimming mode and estimate the active swimming time (tac), not considering coast and drift periods, (ii) estimate near-bottom velocities (Ub) experienced by the fish, rather than using bulk averages (U), (iii) investigate water temperature (T) influence on swimming ability, and (iv) identify a functional relation between Ub, tac and T. Results showed that burst-and-coast swimming mode was increasingly adopted by glass eel, especially when U was higher than 0.3 ms-1. Using U rather than Ub led to an overestimation of the fish swimming performance from 18 to 32%, on average. Under the range of temperatures analyzed (from 8 to 18 °C), tac was strongly influenced and positively related to T. As a final result, we propose a general formula to link near-bottom velocity, water temperature and active swimming time which can be useful in ecological engineering applications and reads as $${\rm{U}}_{\rm{b}}=0.174\cdot \left({{\rm{t}}_{\rm{ac}}}^{-0.36}\cdot {\rm{T}}^{0.77}\right)$$ U b = 0.174 · t ac - 0.36 · T 0.77 .

Endocrine profiles during silvering of the European eel (Anguilla anguilla L.) living in saltwater

2007 ◽  
Vol 57 (4) ◽  
pp. 453-465 ◽  
Author(s):  
Sylvie Dufour ◽  
Vincent van Ginneken ◽  
Caroline Durif ◽  
Jorg Doornbos ◽  
Kees Noorlander ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Thyroid Hormones ◽  
Anguilla Anguilla ◽  
Gonadal Development ◽  
Maximum Activity ◽  
European Eel ◽  
Pca Analysis ◽  
Silver Eel ◽  
Yellow Eel ◽  
Endocrine Profiles

AbstractThe transformation of yellow eel into silver eel is called 'silvering', and takes place prior to migration. This is the first study to provide hormonal profiles of European eel (Anguilla anguilla L.) during silvering. This transformation occurs in association with hormonal surges of testosterone (T) and estradiol (E2) but not with thyroid hormones (TH) and growth hormone (GH) which have a maximum activity in spring and a minimum activity in summer and autumn. It is therefore suggested THs and GH are not important for eel gonadal development in the autumn. Based on PCA analysis with physiological, morphological and endocrinological parameters it is concluded that the transition is gradual and that eels go through several stages.

Evaluation of lethal and nonlethal assessment methods of muscle fat content in European eel (Anguilla anguilla)

2019 ◽  
Vol 76 (4) ◽  
pp. 569-575
Author(s):  
Jan-Dag Pohlmann ◽  
Marko Freese ◽  
Stefan Reiser ◽  
Reinhold Hanel
Keyword(s):  
Morphological Changes ◽  
Life Stage ◽  
Anguilla Anguilla ◽  
Fat Content ◽  
Assessment Methods ◽  
European Eel ◽  
Microwave Measurements ◽  
Fat Reserves ◽  
Key Factor

Individual fat reserves are considered a key factor for the reproductive fitness of the endangered European eel (Anguilla anguilla). In contrast with most established standards, microwave measurements enable the determination of fat contents without sacrificing individual fish, offering a broad range of ecological applications. To test the reliability of nonlethal assessment methods of the muscle fat content in eels, the performance of microwave measurements was compared with the prevailing standard of measuring fat in a distinct subsample of muscle tissue by solvent extraction. Results indicate that either method is prone to error due to physiological and morphological changes during the sexual maturation of eels. Since microwave measurements were systematically affected by life stage and body length, it was possible to calibrate the method accordingly, putting it at least on par with the prevailing standard and further facilitating its use for scientific purposes.

scholarly journals Long-term variation in numbers and biomass of silver eels being produced in two European river systems

2018 ◽  
Vol 75 (5) ◽  
pp. 1627-1637 ◽  
Author(s):  
W Russell Poole ◽  
Ola H Diserud ◽  
Eva B Thorstad ◽  
Caroline M Durif ◽  
Conor Dolan ◽  
...  
Keyword(s):  
Time Series ◽  
Life Stage ◽  
Early Period ◽  
Anguilla Anguilla ◽  
High Water ◽  
Water Levels ◽  
Annual Number ◽  
European Eel ◽  
Silver Eel ◽  
Silver Eels

Abstract The European eel (Anguilla anguilla) population has been in decline at least since the 1960s and reliable regional information, particularly on the spawner production and escapement (i.e. the silver eel life stage), is a requirement of the EU stock recovery regulation. Two comparable time series exist in Burrishoole (Ireland) and Imsa (Norway), with monitoring of total silver eel production since the early 1970s. Numbers of emigrating silver eels fell significantly (p < 0.0001) in the 1980s (breakpoints: Burrishoole 1982; Imsa 1988), in both catchments from >4000 eels per annum to ∼2000 eels per annum. The proportion of male eels dropped and the average size of female eels increased. Biomass of silver eels escaping has remained similar in Burrishoole (1.1/1.2 kg/ha), but not in Imsa (2.1/0.9 kg/ha) between the early period and the 2000s. Factors that govern the onset of eel maturation (silvering) and the annual production of silver eels are little understood. In this paper, the influence of time-lagged environmental variables on silver eel production is examined. Annual variation in the time series was partly (r2 Burrishoole = 0.43, Imsa = 0.46) explained by variation in water temperature and water level. Annual number of migrating eels in both catchments was positively related to summer temperature and summer water flow, negatively related to summer temperatures in the previous year, and in the Burrishoole, also negatively related to high water levels in September/October. The models did not transfer well between catchments, indicating likely catchment specific environmental factors impacting on eel production. The reduction in eel numbers observed in both catchments, accompanied by the change in sex ratio and mean weight of females that contribute to maintain biomass production, calls into question the advisability of basing a spawner escapement recovery target on biomass alone, while numbers and proportions of males decline.

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