scholarly journals Digestive Tract and the Muscular Pharynx/Esophagus in Wild Leptocephalus Larvae of European Eel (Anguilla anguilla)

2021 ◽  
Vol 8 ◽  
Author(s):  
Helene Rønquist Knutsen ◽  
Sune Riis Sørensen ◽  
Peter Munk ◽  
Tora Bardal ◽  
Elin Kjørsvik
Keyword(s):  
Digestive Tract ◽  
Striated Muscle ◽  
Feeding Strategy ◽  
Posterior Part ◽  
Anguilla Anguilla ◽  
Pancreatic Tissue ◽  
European Eel ◽  
Sargasso Sea ◽  
Larval Body ◽  
Leptocephalus Larvae

Several aspects of the biology of European eel (Anguilla anguilla) larvae are still unknown; particularly, information about their functional development and feeding is sparse. In the present study, we histologically characterize the digestive system of wild caught specimens of European eel leptocephalus larvae. The aim was to provide more understanding about how food may be ingested and mechanically processed in the leptocephalus larvae, and to discuss this in the context of its hypothesized feeding strategy. Larvae were caught in the Sargasso Sea during the “Danish Eel Expedition 2014” with the Danish research vessel Dana. The larval sizes ranged from 7.0 to 23.3 mm standard length (SL) at catch. We found that the mouth/pharynx, especially the anterior esophagus, was surrounded by a multi-layered striated muscle tissue and that the epithelium in the mouth/pharynx had a rough filamentous surface, followed by epithelial columnar cells with multiple cilia in the anterior esophagus. This suggests an expandable pharynx/esophagus, well-suited for the transportation of ingested food and likely with a food-crushing or grinding function. The digestive tract of the larvae consisted of a straight esophagus and intestine ventrally aligned within the larval body, and its length was linearly correlated to the larval length (SL). The length of the intestinal part constituted up to 63% of the total length of the digestive tract. The intestinal epithelium had a typical absorptive epithelium structure, with a brush border and a well-developed villi structure. Some cilia were observed in the intestine, but any surrounding muscularis was not observed. The liver was observed along the posterior part of the esophagus, and pancreatic tissue was located anterior to the intestine. Our findings support the hypothesis that the eel leptocephalus may ingest easily digestible gelatinous plankton and/or marine snow aggregates. The muscular esophagus and the ciliated epithelium appear sufficient to ensure nutrient transport and absorption of the ingested food through the digestive tract.

scholarly journals Gelatinous plankton is important in the diet of European eel (Anguilla anguilla) larvae in the Sargasso Sea

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
Daniel J. Ayala ◽  
Peter Munk ◽  
Regitze B. C. Lundgreen ◽  
Sachia J. Traving ◽  
Cornelia Jaspers ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea

scholarly journals Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Alessandro Cresci ◽  
Caroline M. Durif ◽  
Claire B. Paris ◽  
Steven D. Shema ◽  
Anne Berit Skiftesvik ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
Magnetic Compass ◽  
European Eel ◽  
Sargasso Sea ◽  
North African ◽  
Compass Direction ◽  
Tidal Flows ◽  
Glass Eels ◽  
Cardinal Directions ◽  
Magnetic North

Abstract The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic compass for orientation, but whether their magnetic direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic compass direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic compass to memorize the magnetic direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.

Do Leptocephali of the European Eel Swim to Reach Continental Waters? Status of the Question

1998 ◽  
Vol 78 (1) ◽  
pp. 285-306 ◽  
Author(s):  
J.D. McCleave ◽  
P.J. Brickley ◽  
K.M. O'Brien ◽  
D.A. Kistner ◽  
M.W. Wong ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Anguilla Anguilla ◽  
Late Winter ◽  
European Eel ◽  
Sargasso Sea ◽  
North East ◽  
Nutritional Mode ◽  
Mid Atlantic Ridge ◽  
One Year ◽  
European Coast

We examined recent arguments that leptocephali of the European eel,Anguilla anguilla, swim in an oriented manner, rather than drift, to reach the continental shelf of Europe and the Mediterranean Sea. There is a cline of increasing body length of leptocephali from south to north and from west to east from the Mid-Atlantic Ridge (30°W) to the continental shelf, which could represent migration from south-west to north-east, transport eastward at all latitudes, or increased growth rate with latitude. Evidence that this cline is a trend in age of arriving glass eels along the European coast, and that the duration of migration is less than one year, is weak. Ages reported in the literature for specimens from Morocco to The Netherlands were based on the unvalidated assumption that rings in otoliths were deposited daily. The assumption is unwarranted because of low metabolic rate and uncertainty of nutritional mode of leptocephali. If the assumption were accepted, calculated hatching dates of eels arriving at the European coast imply year-round spawning. Lengths of leptocephali in the Sargasso Sea at various times imply that eels spawn only in late winter and spring. Leptocephali contain tiny amounts of muscle, especially aerobic muscle for sustained swimming. They probably have insufficient capability to swim across the Atlantic in the less than 1–2 y reported by others.

scholarly journals The relationship between the moon cycle and the orientation of glass eels ( Anguilla anguilla ) at sea

2019 ◽  
Vol 6 (10) ◽  
pp. 190812 ◽  
Author(s):  
Alessandro Cresci ◽  
Caroline M. Durif ◽  
Claire B. Paris ◽  
Cameron R. S. Thompson ◽  
Steven Shema ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
Lunar Cycle ◽  
Global Scale ◽  
European Eel ◽  
Sargasso Sea ◽  
The Moon ◽  
Detection Mechanism ◽  
Freshwater Habitats ◽  
Glass Eels ◽  
Open Question

Links between the lunar cycle and the life cycle (migration patterns, locomotor activity, pulses in recruitment) of the European eel ( Anguilla anguilla ) are well documented. In this study, we hypothesized that the orientation of glass eels at sea is related to the lunar cycle. The European eel hatches in the Sargasso Sea and migrates across the Atlantic Ocean towards Europe. Upon reaching the continental shelf, the larvae metamorphose into glass eels and migrate up the estuaries, where some individuals colonize freshwater habitats. How glass eels navigate pelagic waters is still an open question. We tested the orientation of 203 glass eels in a transparent circular arena that was drifting in situ during the daytime, in the coastal Norwegian North Sea, during different lunar phases. The glass eels swimming at sea oriented towards the azimuth of the moon at new moon, when the moon rose above the horizon and was invisible but not during the other moon phases. These results suggest that glass eels could use the moon position for orientation at sea and that the detection mechanism involved is not visual. We hypothesize a possible detection mechanism based on global-scale lunar disturbances in electrical fields and discuss the implications of lunar-related orientation for the recruitment of glass eels to estuaries. This behaviour could help glass eels to reach the European coasts during their marine migration.

scholarly journals A mechanical approach to understanding the impact of the nematode Anguillicoloides crassus on the European eel swimbladder

2020 ◽  
Vol 223 (17) ◽  
pp. jeb219808
Author(s):  
Helen A. L. Currie ◽  
Nicholas Flores Martin ◽  
Gerardo Espindola Garcia ◽  
Frances M. Davis ◽  
Paul S. Kemp
Keyword(s):  
Mechanical Damage ◽  
Severe Infection ◽  
Anguilla Anguilla ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
European Eel ◽  
Sargasso Sea ◽  
Mechanical Integrity ◽  
The Impact ◽  
Anguillicoloides Crassus

ABSTRACTOne of the most detrimental factors in the drastic decline of the critically endangered European eel (Anguilla anguilla) was the inadvertent introduction of the invasive nematode Anguillicoloides crassus. Infection primarily affects the swimbladder, a gas-filled organ that enables the eel to control its depth in the water. A reduction in swimbladder function may be fatal for eel undergoing their spawning migration to the Sargasso Sea, a journey of over 5000 km. Although the physiological damage caused by this invasive parasite is well studied through the use of quantifiable gross pathological indices, providing a good measure of the swimbladder health status, they cannot separate the role of mechanical and morphological damage. Our study examined the appropriateness of three commonly used indices as a measure of mechanical damage by performing uniaxial tensile tests on swimbladder specimens obtained from an infected eel population. When the test results were compared with the gross pathological indices it was found that thickness correlated most strongly with mechanical damage, both confirming and, more importantly, explaining the counterintuitive findings of earlier work. In a damaged swimbladder, the immune response leads to a trade-off; increasing wall thickness raises the pressure required for organ rupture but decreases strength. The results indicate that for moderate infection the mechanical integrity of the swimbladder can be maintained. For severe infection, however, a reduction in mechanical integrity may reach a tipping point, thereby affecting the successful completion of their oceanic migration.

scholarly journals Problems and perspectives of artificial reproduction and conservation of the european eel (Anguilla anguilla (Linnaeus, 1758)) (a review)

2021 ◽  
pp. 34-44
Author(s):  
V. Bekh ◽  
◽  
I. Kononenko ◽  
R. Kononenko ◽  
◽  
...  
Keyword(s):  
Large Scale ◽  
Technological Development ◽  
Natural Populations ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
Artificial Reproduction ◽  
Promising Area ◽  
Stable Source ◽  
The Impact

Purpose. Rearing of the European eel (Anguilla anguilla) is a promising area of aquaculture, the development of which in Ukraine and the world is constrained by several factors. Spawning, egg incubation, lack of a stable source of supply of fish seeds – these and other problems, as well as the importance of such studies form a basis for finding approaches for their solution and conducting new large-scale studies. This area attracts attention of scientists, there are certain results and achievements; however, they are still not enough to solve the problems of artificial reproduction of the European eel. Findings. The authors revised, analysed and systematized literature sources focused on the study of the European eel. As a result, it was possible to identify the main achievements and shortcomings in this area, which are promising for further study. In addition, we identified some obstacles faced by scientists and analysed available methods for their solving. Practical value. This review can be used to stimulate new studies and technological development towards industrial cultivation of eel in Ukraine, which will allow reducing the impact on natural populations of this species and stabilize its number in the natural environment. In addition, the authors of the article intend to draw attention of scientists and manufacturers to the perspectives and problems of growing and studying the European eel. Key words: European eel, glass eel, leptocephali, migration, Sargasso Sea, cultivation, fish seeds.

scholarly journals How the European eel ( Anguilla anguilla ) loses its skeletal framework across lifetime

2016 ◽  
Vol 283 (1841) ◽  
pp. 20161550 ◽  
Author(s):  
Tim Rolvien ◽  
Florian Nagel ◽  
Petar Milovanovic ◽  
Sven Wuertz ◽  
Robert Percy Marshall ◽  
...  
Keyword(s):  
Bone Loss ◽  
Mechanical Stability ◽  
North Atlantic Ocean ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
Morphological Transformation ◽  
The North ◽  
Life Cycle Stages ◽  
Cellular Bone

European eels ( Anguilla anguilla ) undertake an impressive 5 000 km long migration from European fresh waters through the North Atlantic Ocean to the Sargasso Sea. Along with sexual maturation, the eel skeleton undergoes a remarkable morphological transformation during migration, where a hitherto completely obscure bone loss phenomenon occurs. To unravel mechanisms of the maturation-related decay of the skeleton, we performed a multiscale assessment of eels' bones at different life-cycle stages. Accordingly, the skeleton reflects extensive bone loss that is mediated via multinucleated bone-resorbing osteoclasts, while other resorption mechanisms such as osteocytic osteolysis or matrix demineralization were not observed. Preserving mechanical stability and releasing minerals for energy metabolism are two mutually exclusive functions of the skeleton that are orchestrated in eels through the presence of two spatially segregated hard tissues: cellular bone and acellular notochord. The cellular bone serves as a source of mineral release following osteoclastic resorption, whereas the mineralized notochord sheath, which is inaccessible for resorption processes due to an unmineralized cover layer, ensures sufficient mechanical stability as a part of the notochord sheath. Clearly, an eel's skeleton is structurally optimized to meet the metabolic challenge of fasting and simultaneous sexual development during an exhausting journey to spawning areas, while the function of the vertebral column is maintained to achieve this goal.

scholarly journals Panmixia in the European eel: a matter of time…

2005 ◽  
Vol 272 (1568) ◽  
pp. 1129-1137 ◽  
Author(s):  
Johan Dannewitz ◽  
Gregory E Maes ◽  
Leif Johansson ◽  
Håkan Wickström ◽  
Filip A.M Volckaert ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Genetic Structure ◽  
North Atlantic ◽  
Isolation By Distance ◽  
Temporal Stability ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
The North ◽  
Temporal Genetic Variation

The European eel ( Anguilla anguilla L.) has been a prime example of the panmixia paradigm because of its extraordinary adaptation to the North Atlantic gyral system, semelparous spawning in the Sargasso Sea and long trans-oceanic migration. Recently, this view was challenged by the suggestion of a genetic structure characterized by an isolation-by-distance (IBD) pattern. This is only likely if spawning subpopulations are spatially and/or temporally separated, followed by non-random larval dispersal. A limitation of previous genetic work on eels is the lack of replication over time to test for temporal stability of genetic structure. Here, we hypothesize that temporal genetic variation plays a significant role in explaining the spatial structure reported earlier for this species. We tested this by increasing the texture of geographical sampling and by including temporal replicates. Overall genetic differentiation among samples was low, highly significant and comparable with earlier studies ( F ST =0.0014; p <0.01). On the other hand, and in sharp contrast with current understandings, hierarchical analyses revealed no significant inter-location genetic heterogeneity and hence no IBD. Instead, genetic variation among temporal samples within sites clearly exceeded the geographical component. Our results provide support for the panmixia hypothesis and emphasize the importance of temporal replication when assessing population structure of marine fish species.

scholarly journals Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels

2010 ◽  
Vol 277 (1700) ◽  
pp. 3593-3599 ◽  
Author(s):  
Peter Munk ◽  
Michael M. Hansen ◽  
Gregory E. Maes ◽  
Torkel G. Nielsen ◽  
Martin Castonguay ◽  
...  
Keyword(s):  
Life Cycle ◽  
Life Histories ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
American Eel ◽  
Wide Range ◽  
Frontal Processes ◽  
Glass Eels ◽  
Atlantic Eels

Anguillid freshwater eels show remarkable life histories. In the Atlantic, the European eel ( Anguilla anguilla ) and American eel ( Anguilla rostrata ) undertake extensive migrations to spawn in the oceanic Sargasso Sea, and subsequently the offspring drift to foraging areas in Europe and North America, first as leaf-like leptocephali larvae that later metamorphose into glass eels. Since recruitment of European and American glass eels has declined drastically during past decades, there is a strong demand for further understanding of the early, oceanic phase of their life cycle. Consequently, during a field expedition to the eel spawning sites in the Sargasso Sea, we carried out a wide range of dedicated bio-physical studies across areas of eel larval distribution. Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical–biological linkages in the life-cycle completion of Atlantic eels.

How does the European eel (Anguilla anguilla) retain its population structure during its larval migration across the North Atlantic Ocean?

2006 ◽  
Vol 63 (1) ◽  
pp. 90-106 ◽  
Author(s):  
A James Kettle ◽  
Keith Haines
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
Larval Migration ◽  
The North ◽  
The North Atlantic ◽  
And Migration

A Lagrangian model is presented of the current-carried migration of the leptocephali (larvae) of the European eel (Anguilla anguilla) across the North Atlantic Ocean from the spawning area in the Sargasso Sea to the adult range in Europe and North Africa. The success of larvae in crossing the Atlantic Ocean and reaching particular latitude bins on the eastern side depended strongly on starting location in the Sargasso Sea and migration depth. In the model domain, silver eel spawners can develop strategies for spawning location and migration depth to preferentially target particular regions in the adult range. This observation may help to explain the presence of gradients in molecular markers in eel samples collected across Europe. Spawning in the period of late winter – spring maximizes the average food availability along the 2-year larval trajectory. The fastest transatlantic larval migration in the model is about 2 years, and the route to Europe takes most of the larvae past the east coast of North America in the first year. These model results are consistent with the hypothesis that the European and American eel (Anguilla rostrata) could separate themselves on different sides of the Atlantic Ocean on the basis of the different durations of their larval stages.

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