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PubMed2002

Two isoforms of the Na+/K+/2Cl- cotransporter are expressed in the European eel (Anguilla anguilla).

Two cDNA isoforms of the NKCC1 secretory cotransporter have been isolated from the European eel. The NKCC1a isoform exhibited mRNA expression in a wide range of tissues in a similar fashion to mammals, whereas NKCC1b was expressed primarily in the brain. The effect of freshwater (FW) to seawater (SW) transfer on NKCC1a expression was dependent on the developmental stage. In non-migratory yellow eels, NKCC1a mRNA expression in the gill was transiently up-regulated 4.3-fold after 2 days but also subsequently by 2.5-6-fold 3 weeks after SW transfer. Gill NKCC1a expression was localised mainly in branchial chloride cells of SW acclimated yellow eels. In contrast to yellow eels, NKCC1a mRNA abundance was not significantly different following SW acclimation in silver eel gill. NKCC1a mRNA abundance decreased in the kidney following SW acclimation and this may correlate with lower tubular ion/fluid secretion and urine flow rates in SW teleosts. Kidney NKCC1a mRNA expression in silver eels was also significantly lower than in yellow eels, suggesting some pre-acclimation of mRNA levels. NKCC1a mRNA was expressed at similar low levels in the middle intestine of FW- and SW-acclimated yellow or silver eels, suggesting the presence of an ion secretory mechanism in this gut segment.

Acclimatization↗
PubMed2003

Expression of a biologically active recombinant follicle stimulating hormone of Japanese Eel Anguilla japonica using methylotropic yeast, Pichia pastoris.

In the Japanese eel Anguilla japonica, the administration of exogenous GTH is necessary for the artificial induction and completion of gonadal maturation due to its GTH deficiency under captive conditions. The isolation of native eel GTH has not been accomplished, which has made it difficult to fully elucidate the biological functioning of the two GTHs (FSH and LH) in eel. In this study, we attempted to produce a recombinant Japanese eel GTH (rjeFSH) having biological activity using methylotrophic yeast, Pichia pastoris in order to gain more understanding of the functioning of GTH in this species. An expression vector in which jeFSHbeta and GTHalpha subunit cDNAs were tandemly connected was constructed. P. pastoris was transformed with the vector, and rjeFSH was expressed. The rjeFSH thus expressed was detected by Western blot analysis. The glycoprotein fraction of the yeast culture supernatant was separated by native PAGE, and a band showed positive reaction with anti-GTHalpha and FSHbeta antisera similarly, suggesting that both subunits are associated. After deglycosylation, both subunits were decreased in molecular mass, indicating that rjeFSH was glycosylated. In in vitro assay, rjeFSH stimulated the release of testosterone and 11-ketotestosterone from immature eel testis, whereas release was not stimulated in maturing eel testis. This is the first report investigating the biological activity of eel GTH using the recombinant eel FSH.

Androgens↗
PubMed2002

Kinetics of radiolabelled silver uptake and depuration in the gills of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation.

We examined the influence of speciation on the kinetics of silver uptake and depuration in the gills of two freshwater fish, the rainbow trout (Oncorhynchus mykiss) which has high branchial Na(+) and Cl(-) uptake rates and is relatively sensitive to silver, and the European eel (Anguilla anguilla, yellow stage) which has low ion uptake rates and is relatively resistant to silver. Fish previously acclimated to the appropriate chloride level were exposed to 110mAgNO(3) (1.3 microg l(-1), sublethal) for 24 h in synthetic softwater with either low (10 microM) or high (1200 microM) chloride concentration, and then followed over a subsequent 67-day post-exposure period in silver-free water of the same chloride content. The exposures were therefore mainly to the free ion, Ag(+) in the low chloride water versus mainly to the neutral aqueous complex, AgCl(aq) in the high chloride water. In trout, but not in eel, water chloride is known to protect against physiological disturbances and toxicity caused by Ag(+). In both fish species, at both chloride levels, silver uptake exhibited complex kinetics. Gill silver loading occurred slowly until 6 h, then rose greatly to a peak at 12 h, followed by significant net depuration thereafter during continued exposure. By 24 h, net gill loading was three- to fivefold greater from AgCl(aq) than from Ag(+) exposure in both species, and threefold greater in trout than in eel under both conditions, with trout holding a lower fraction of the whole body burden in their gills. During the post-exposure period, depuration of silver from the gills occurred rapidly in trout, but very slowly in eel, such that gill silver burdens were greater in eel throughout the 67-day period on both an absolute and relative basis (e.g. 35% of whole body burden in eel versus <3% in trout at day 8). The kinetics of depuration were described by two phase exponential models, with break points between the fast and slow phases at 1 and 15 days for trout and eel, respectively. We conclude that speciation affects not only uptake rates but also the kinetics of depuration. When silver is loaded from AgCl(aq) it is clearly more labile than from Ag(+) exposures, with 1.6-1.8-fold greater loss rates during the fast phases in both species. Differences in branchial silver uptake between eel and trout correlate well with differences in acute toxicity, but are not as large as differences in ion uptake rates. The complex time-dependent patterns of gill loading, and the higher loading from AgCl(aq) than from Ag(+), mean that gill total silver burden is not an appropriate endpoint for biotic ligand modelling.

Adaptation, Physiological↗
PubMed2003

Parasite infracommunity diversity in eels: a reflection of local component community diversity.

The intestinal macroparasite communities of freshwater eels (Anguilla anguilla) captured in the south of England from Windsor (River Thames) during August 2001, and Leckford (River Test) during late June/July 2000, are reported for the first time. Parasite component communities were among the most species rich and diverse recorded from European eels. A total of 13 intestinal macroparasite species were encountered during the study, 8 from each eel host population with 3 being common to both. Acanthocephalans, nematodes and cestodes were recovered from each host population. Eels from Windsor additionally harboured Nicolla gallica (Digenea), which was also the most prevalent and abundant macroparasite species in these hosts. Each component community followed a log normal rank abundance distribution and demonstrated reduced species dominance and increased species equitability compared with previous studies. As such, the study component communities were suitable for testing the hypothesis of low infracommunity diversity in European eel hosts. Specifically, this hypothesis predicts that the intestinal macroparasite infracommunities of European eels are species-poor, displaying low density and diversity with high dominance, irrespective of component community diversity, and that this may be more pronounced in UK host populations. This hypothesis was not upheld; study findings demonstrate that higher infracommunity diversity in eel hosts is possible, and suggest that infracommunity diversity in individual eel hosts may be a simple, stochastic reflection of component community diversity.

Anguilla↗
PubMed1997

Detection of low phosphorus contents in neurofilaments of squid axons by Image-EELS contrast spectroscopy.

We show that Image-EELS is suitable for detecting relatively low phosphorus concentrations in very small axoplasmic structures of squid axons. Imaging plates and a CCD camera were used as electron sensors. From image series spanning a certain energy-loss range EELS (electron energy-loss spectra) were derived by averaging read-outs from many axoplasmic particles (APs). The ratio of these spectra to spectra of the background was plotted, showing the contrast modulation as a function of the energy loss. This new approach is called EELC (electron energy-loss-dependent contrast spectroscopy). A distinct phosphorus signal was found in APs of presynaptic terminals of the squid giant synapse, in the peripheral giant axon and, as controls, in ribosomes. Biochemical experiments supported this result. In neurofilament-enriched pellets a phosphorus signal could be directly detected by serial EELS and in electron spectroscopic micrographs. After dephosphorylation of either the pellets or the extruded axoplasm with alkaline phosphatase, phosphorus signals in electron spectroscopic micrographs were absent or much reduced in size and intensity. With Image-EELS inherent limitations of traditional element detection modes in energy filtering transmission electron microscopy can be overcome. Compared with serial EELS, the selective analysis of small areas with irregular shape is possible with greatly improved signal-to-noise ratio. The identification of the element-peak in Image-EEL spectra directly proves the presence of the element within the region of interest. For small peaks, the visualization is facilitated by the contrast presentation (EELC). However, the background subtraction modes used for elemental mapping in electron spectroscopic imaging are subject to uncertainties when elemental ionization edges like the P1,2,3 edge are examined. Imaging plates are very sensitive electron sensors with a wide dynamic range. Unlike photographic emulsions, they allow acquisition of image series covering a large energy-loss range without normalization of exposure times, and direct extraction of EEL spectra. Thus, the combination of Image-EELS and imaging plates is proposed as an efficient new tool for analytical electron microscopy.

Animals↗
PubMed2003

Decline of North Atlantic eels: a fatal synergy?

Panmictic species pose particular problems for conservation because their welfare can be addressed effectively only on a global scale. We recently documented by means of microsatellite analysis that the European eel (Anguilla anguilla) is not panmictic but instead shows genetic isolation by distance. In this study, we extended the analysis to the American eel (A. rostrata) by applying identical analytical procedures and statistical power. Results obtained for the American eel were in sharp contrast with those obtained for the European eel: the null hypothesis of panmixia could not be rejected, and no isolation by distance was detected. This implies that the species must be managed as a single population. Using Bayesian statistics, we also found that the effective population sizes for both species were surprisingly low and that the populations had undergone severe contractions, most probably during the Wisconsinan glaciation. The apparent sensitivity of eels to climatic changes affecting the strength and position of the Gulf Stream 20,000 years ago is particularly worrying, given the effects of the ongoing global warming on the North Atlantic climate. Moreover, additional short-term stresses such as surging glass eel prizes, overfishing and lethal parasitic infections negatively affect eel population size. The fascinating transatlantic migration and life cycle of Atlantic eels is also their Achilles' heel as these negative short- and long-term effects will probably culminate in a fatal synergy if drastic conservation measures are not implemented to protect these international biological resources.

Anguilla↗
PubMed1975

Kidney function of the American eel Anguilla rostrata.

Urine formation in the eel, acclimated to freshwater (FW) and seawater (SW) was studied. SW eels maintained higher plasma and urine osmotic and ionic concentrations than FW eels. Polyethylene-1,2-glycol-14C (PEG-14C) clearance was 29% greater than methoxy-inulin-3H clearance. PEG-14C clearance was considered to be the glomerular filtration rate (GFR). The GFR of SW and FW eels did not differ. Urine flow rate in SW eels was one-third of that in FW eels. The primary urinary solutes in both groups were Na and Cl. Apparently, tubular fluid secretion occurred in FW and, to a lesser degree, in SW eels. With the assumption that water reabsorption was secondary to Na reabsorption in the kidney, the clearance data were used to evaluate all possible explanations for what appeared to be fluid secretion. The data were inconsistent with the possibility that GFR had been underestimated due to glomerular sieving of PEG or active or passive reabsorption of the marker, but consistent with tubular fluid secretion. Furosemide caused diuresis in both groups of eels apparently by inhibition of Na reabsorption in the distal tubule, but it had no effect on the apparent tubular fluid secretion. Tubular ion secretion could not be conclusively implicated as a driving force for fluid secretion. However, the possibility of K, Ca, or Mg secretion in a proximal segment followed by reabsorption in a more distal part of the nephron was not ruled out.

Acclimatization↗
PubMed2004

Magnetic sense in the Japanese eel, Anguilla japonica, as determined by conditioning and electrocardiography.

Magnetosensitivity of the Japanese eel, Anguilla japonica, was examined by conditioning and electrocardiography. Marine eels, river eels and farmed eels were conditioned to an imposed magnetic field ranging from 12,663 nT to 192,473 nT parallel to the fish body, which was placed along the earth's west-east axis. Electrocardiograms were recorded with electrodes placed close to the fish body inside a PVC pipe shelter. After 10-40 conditioning runs, all the eels exhibited a significant conditioned response (i.e. slowing of the heart beat) to a 192,473 nT magnetic field and even to a 12,663 nT magnetic field, respectively equivalent to 5.92x and 0.38x the horizontal geomagnetic field (32,524 nT) at our laboratory. The west-east vector of the imposed magnetic field (12,663 nT) combined with that of the geomagnetic field and produced a horizontal resultant magnetic field of 21 degrees easterly. Therefore, Japanese eel are magnetosensitive whether they are at sea, in the river or in the farm. Results of the present study were compared with those of past studies that showed no magnetic sense in the American eel, Anguilla rostrata, and the European eel, Anguilla anguilla.

Anguilla↗
PubMed2001

How the body contributes to the wake in undulatory fish swimming: flow fields of a swimming eel (Anguilla anguilla).

Undulatory swimmers generate thrust by passing a transverse wave down their body. Thrust is generated not just at the tail, but also to a varying degree by the body, depending on the fish's morphology and swimming movements. To examine the mechanisms by which the body in particular contributes to thrust production, we chose eels, which have no pronounced tail fin and hence are thought to generate all their thrust with their body. We investigated the interaction between body movements and the flow around swimming eels using two-dimensional particle image velocimetry. Maximum flow velocities adjacent to the eel's body increase almost linearly from head to tail, suggesting that eels generate thrust continuously along their body. The wake behind eels swimming at 1.5 Ls(-1), where L is body length, consisted of a double row of double vortices with little backward momentum. The eel sheds two vortices per half tail-beat, which can be identified by their shedding dynamics as a start-stop vortex of the tail and a vortex shed when the body-generated flows reach the 'trailing edge' and cause separation. Two consecutively shed ipsilateral body and tail vortices combine to form a vortex pair that moves away from the mean path of motion. This wake shape resembles flow patterns described previously for a propulsive mode in which neither swimming efficiency nor thrust is maximised but sideways forces are high. This swimming mode is suited to high manoeuvrability. Earlier recordings show that eels also generate a wake reflective of maximum swimming efficiency. The combined findings suggest that eels can modify their body wave to generate wakes that reflect their propulsive mode.

Anguilla↗
PubMed1974

Some factors regulating water intake by the eel, Anguilla japonica.

1. Internal as well as external factors affecting water ingestion in the eel were analysed using oesophagus-cannulated eels. 2. Acute withdrawal of the blood induced an immediate drinking response in the freshwater eel, whereas infusion of a large amount of hypertonic saline interrupted the copious drinking observed in the seawater eel. 3. The freshwater eel responded to slow infusion of hypertonic NaCl solution by constant drinking. 4. Inhibition of drinking was observed in the seawater eel by distension of the stomach or intestine with isotonic mannitol solution. 5. The freshwater eel started drinking immediately after transfer to sea water, and stopped drinking immediately after return to fresh water. 6. Application of various salt solutions revealed that chloride ions are responsible for the induction of drinking in sea water. 7. Stimulation of drinking by chloride ions and inhibition by fresh water may be an anticipatory drinking behaviour, which facilitates adaptation of eels to both sea water and fresh water.

Anguilla↗
PubMed2001

The swimbladder nematode Anguillicola crassus in American eels (Anguilla rostrata) from middle and upper regions of Chesapeake Bay.

The patterns of infection of American eels Anguilla rostrata, with the introduced swimbladder nematode Anguillicola crassus, in tributaries of middle and upper Chesapeake Bay are described. A total of 423 subadult eels was collected from 8 Bay tributaries from spring 1998 to fall 1999. Also, 30 elvers were collected from Ocean City, Maryland, in spring 1998. The numbers of juvenile and adult specimens of A. crassus in the swimbladder wall and lumen were counted. No elvers were infected. In subadult eels, prevalence of adult and juvenile stages combined ranged from 13% to 82%; mean intensity ranged from 2.6 to 9.0 worms per eel. Infection levels were highest for Susquehanna River eels (northernmost river) and lowest in the southernmost sites: St. Jerome's Creek and the Pocomoke River. Although eels from these 2 localities were larger, the low infection rates there are most likely due to reduced transmission in higher salinity water and not to eel size. Eels with both adult and juvenile stages of A. crassus were more common than expected by chance. This might be explained by inhibition of juveniles migrating into the swimbladder lumen when adults are already present there.

Air Sacs↗
PubMed1999

Natural mass infection by heterophyid metacercariae in aquacultured Japanese eel in Taiwan.

A natural mass infection of heterophyid metacercariae in aquacultured Japanese eel Anguilla japonica in Taiwan was observed. Of the 28,000 adult eels in 2 ponds, about 25,000 (90%) showed swollen, cloudy and white eyes. Although morbidity was about 90%, there was no mortality among the affected eels. Histopathological sections showed edema and hemorrhage of the eye. Numerous metacercariae were observed in the muscle tissues around the eyeball, the subcutaneous tissue and even in the cartilage. Of the 6 eels digested with artificial gastric juice, all were found to contain metacercariae in their muscle tissues. The average number of metacercariae recovered from the 6 eels was 1219, with a range of 50 to 3762. These metacercariae, when fed orally to immunodeficient (scid) mice, developed into adult worms which were identified as Procerovum cheni Hsu 1950. The naturally infected eels were transferred to a new pond without snails and their eye lesions were not apparent anymore after 2 wk. In a follow-up investigation, 19 of 20 apparently healthy eels in a nearby aquaculture farm were found to harbour metacercariae in their muscles. However, the number of the metacercariae ranged from 1 to 14, with an average of 4.21. This is the first report of heterophyid metacercariae causing mass morbidity in aquacultured eels.

Anguilla↗
PubMed1985

On the heterogeneity of Purkinje neurons in vertebrates. Cytochemical and morphological studies of chromatin during eel (Anguilla anguilla L.) life cycle.

The relationship between the heterogeneity of Purkinje cell chromatin and the functional involvement of cerebellum has been analyzed comparing two stages of eel life cycle (yellow eel and silver eel) which are characterized by a different degree of swimming activity. The DNA content and the chromatin condensation have been studied by means of microdensitometry (Feulgen-DNA, Feulgen-DNA/area), microfluorometry (DNA after intercalation with Propidium Iodide at low and high concentration) and electron microscopy. In the transition from the yellow eel to the silver eel, the Purkinje cell heterogeneity undergoes variations. In the silver eel, which shows a higher swimming activity, high Feulgen-DNA and Propidium Iodide-DNA (H2c to 4c) were more frequent and a greater heterogeneity in the chromatin condensation was observed. In particular, the changes were more evident in the lobus vestibulolateralis; mainly in this area, which receives inputs from the lateral line, the Purkinje cells are scattered in the molecular layer. On the contrary, in the yellow eel these large cells occupy the zone near or within the granular layer. The data suggest a relationship between the degree of heterogeneity of Purkinje cells and the afferent systems of the cerebellar areas examined. The changes of cerebellar cytoarchitectonics may be expression of the higher degree of the swimming activity of silver eel.

Anguilla↗
PubMed1996

Skin morphology and cytology in marine eels adapted to different lifestyles.

BACKGROUND: Moray eels (Muraenidae, Pisces) are among the largest benthic predators of littoral habitats, particularly in warm seas and coral reefs. They seek food either by olfaction or visually, moving across the pebbles and rocks. Their skin forms a strong, protective layer. This study examines the comparative morphology and cytology of the skin of moray eels adapted to such lifestyles. METHODS: The studied eels were collected in the Gulf of Aqaba, Red Sea and sacrificed by an overdose of MS222. Skin selections from different body sites were dissected and fixed for light and electron microscopy. RESULTS: The skin of moray eels (Siderea grisea, Lycodontis nudivomer, Gymnothorax undulata, G. hepaticus, Rhinomuraena amboensis) and the heterocongrid garden eel (Gorgasia sillneri) reveal considerable adaptation of the integument to their different lifestyles, on and within the various bottom substrata. All the eels studied featured skin comprising a multilayered, stratified epidermis and a compact, collagenous dermis, with thickness of up to 2 mm, much thicker than that observed in their free-swimming relatives. The thickness and cytology of the two skin layers differ in the various species on different body sites within the same species and also changes with age. Pronounced differences were observed in the number and type of mucus-producing cells in the epidermis. In S. grisea, the entire body is covered by a multiple layer of goblet cells, whereas in G. sillneri, sacciform cells predominate, particularly on the caudal part of the body where they form an uninterrupted layer, replacing the supporting cells that surround them. These cells are also dominant in R. amboensis. The two latter species are sand-dwelling and the copious production of slime from these cells enables the adhesion of sand granules to their burrow walls. In Gorgasia, a special morphological adaptation was also observed in its pointed tail-end where the very strong dermal collagen forms a rigid device for digging tail-first into the sand. CONCLUSION: The differing thicknesses and cytological developments in the skin of marine eels protect these crawling and digging creatures against abrasive interaction with their sea bottom habitat.

Adaptation, Physiological↗
PubMed1990

Amino acid sequence and relative biological activity of a natriuretic peptide isolated from eel brain.

A peptide exhibiting natriuretic and vasodepressor activity was isolated from eel brains. Its amino acid sequence was found to be similar to, but distinct from, that of the eel atrial natriuretic peptide (ANP), and it is characterized by the absence of the C-terminal sequence that follows the second-half cystine. The extent of sequence homology of this peptide to known mammalian brain natriuretic peptides (BNPs) is greater than to ANPs. Therefore, we have named this peptide "eel BNP-like peptide". The isolation of this peptide provides the first evidence for the presence of two different molecular types of natriuretic peptide in a single non-mammalian species. The potency of the eel BNP-like peptide relative to that of human ANP, in terms of its vasodepressor activity, was 117 in the eel, 1.7 in the quail, and 0.08 in the rat. Thus, eels exhibit a high degree of sensitivity to this native peptide just as they do to eel ANP.

Amino Acid Sequence↗
PubMed1991

A novel natriuretic peptide isolated from eel cardiac ventricles.

A new natriuretic peptide, which exhibits the entire spectrum of actions known to be characteristic of atrial and brain natriuretic peptides (ANP and BNP), was isolated from eel cardiac ventricles and has been named ventricular natriuretic peptide (VNP). The primary structure of eel VNP is characterized by its uniquely long C-terminal 'tail' that extends from the second half-cystine. Thus, eel VNP appears to be a novel natriuretic peptide of a type not found in mammals. With respect to natriuretic (rat) and vasodepressor (rat and eel) activities, eel VNP is much more potent than human ANP in eels and almost equipotent in rats. Strong tachyphylaxis is observed for the vasodepressor effect in both rats and eels, whereas it is not observed for the natriuretic effect in rats.

Amino Acid Sequence↗
PubMed2005

Integrative approach to osmoregulatory action of atrial natriuretic peptide in seawater eels.

Atrial natriuretic peptide (ANP) reduces plasma Na+ concentration and promotes seawater (SW) adaptation in SW eels. However, little is known about the mechanisms for the hyponatremic effect of ANP. In order to evaluate the role of ANP in the whole-body Na+ homeostasis of marine teleost, we reviewed previous in vivo experiments using exogenously administered ANP and present additional experiments to assess the role of endogenous ANP in Na+ homeostasis in conscious SW eels. The Na+ influx and efflux rate across the body surfaces including the gills measured with isotopic 22Na were not altered by the hyponatremic dose (5 pmol kg-1 min-1) of ANP infusion in SW eels. ANP infusion also had no effect on renal Na+ excretion in SW eels. In contrast, ANP strongly inhibited drinking, and the inhibition was quantitatively correlated with the hyponatremic effect of ANP. Further, intestinal absorption of Na+ was inhibited by ANP as examined in situ using intestinal sac in conscious SW eels. The combined inhibitory actions of ANP on drinking and intestinal absorption were sufficient to explain the decrease in plasma Na+ concentration. In addition, removal of endogenous circulating ANP by immunoneutralization increased plasma Na+ concentration with a concomitant increase in drinking rate in SW eels. These results strongly suggest that endogenous ANP is involved in the hyponatremic regulation through actions on drinking, and probably on intestine, in SW eels.

Acclimatization↗
PubMed2000

Methyl mercury bioaccumulation in long-finned eels, Anguilla dieffenbachii, from three rivers in Otago, New Zealand.

This research focuses on mercury (Hg) bioaccumulation in New Zealand long-tinned eels (Anguilla dieffenbachii) from the aquatic environment. Total Hg (HgT) and methyl mercury (MeHg) concentrations were determined in muscle tissue from eels living in three South Island rivers dominated respectively by urban, native bush and agricultural land-uses. Most of the Hg in eels was MeHg (> 84%) and the MeHg concentrations increased linearly with both length and eel age for a given river habitat. The annual growth rates for eels from the urban and agricultural streams were greater than for eels from the native bush stream. The average MeHg accumulation rate was significantly higher for the eels in the agricultural stream compared with either the urban or native bush catchments. These results are probably due to a combination of factors and further investigations in the lower food web are necessary to elucidate the exact mechanisms of MeHg bioaccumulation in these creatures.

Age Factors↗