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1
BUTCHER, M. "Eel-traps without Eels". Journal of Design History 10, n. 4 (1 gennaio 1997): 417–29. http://dx.doi.org/10.1093/jdh/10.4.417.
Testo completo
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Catania, Kenneth C. "An Optimized Biological Taser: Electric Eels Remotely Induce or Arrest Movement in Nearby Prey". Brain, Behavior and Evolution 86, n. 1 (2015): 38–47. http://dx.doi.org/10.1159/000435945.
Testo completoAbstract (sommario):
Despite centuries of interest in electric eels, few studies have investigated the mechanism of the eel's attack. Here, I review and extend recent findings that show eel electric high-voltage discharges activate prey motor neuron efferents. This mechanism allows electric eels to remotely control their targets using two different strategies. When nearby prey have been detected, eels emit a high-voltage volley that causes whole-body tetanus in the target, freezing all voluntary movement and allowing the eel to capture the prey with a suction feeding strike. When hunting for cryptic prey, eels emit doublets and triplets, inducing whole-body twitch in prey, which in turn elicits an immediate eel attack with a full volley and suction feeding strike. Thus, by using their modified muscles (electrocytes) as amplifiers of their own motor efferents, eel's motor neurons remotely activate prey motor neurons to cause movement (twitch and escape) or immobilization (tetanus) facilitating prey detection and capture, respectively. These results explain reports that human movement is ‘frozen' by eel discharges and shows the mechanism to resemble a law-enforcement Taser.
3
Catania, Kenneth. "The shocking predatory strike of the electric eel". Science 346, n. 6214 (4 dicembre 2014): 1231–34. http://dx.doi.org/10.1126/science.1260807.
Testo completoAbstract (sommario):
Electric eels can incapacitate prey with an electric discharge, but the mechanism of the eel’s attack is unknown. Through a series of experiments, I show that eel high-voltage discharges can activate prey motor neurons, and hence muscles, allowing eels to remotely control their target. Eels prevent escape in free-swimming prey using high-frequency volleys to induce immobilizing whole-body muscle contraction (tetanus). Further, when prey are hidden, eels can emit periodic volleys of two or three discharges that cause massive involuntary twitch, revealing the prey’s location and eliciting the full, tetanus-inducing volley. The temporal patterns of eel electrical discharges resemble motor neuron activity that induces fast muscle contraction, suggesting that eel high-voltage volleys have been selected to most efficiently induce involuntary muscle contraction in nearby animals.
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Tambets, Meelis, Einar Kärgenberg, Ain Järvalt, Finn Økland, Martin Lykke Kristensen, Anders Koed e Priit Bernotas. "Migrating silver eels return from the sea to the river of origin after a false start". Biology Letters 17, n. 9 (settembre 2021): 20210346. http://dx.doi.org/10.1098/rsbl.2021.0346.
Testo completoAbstract (sommario):
The European eel's singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river of origin after spending up to a year in the marine environment. After migrating to the Baltic Sea, 21% of the silver eels, tagged with acoustic transmitters, returned to the Narva River. Half returned 11–12 months after moving to the sea, with 15 km being the longest upstream movement. The returned eels spent up to 33 days in the river and migrated to the sea again. The fastest specimen migrated to the outlet of the Baltic Sea in 68 days after the second start—roughly 1300 km. The surprising occurrence of returning migrants has implications for sustainable management and protection of this critically endangered species.
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Catania, Kenneth C. "Electric Eels Wield a Functional Venom Analogue". Toxins 13, n. 1 (10 gennaio 2021): 48. http://dx.doi.org/10.3390/toxins13010048.
Testo completoAbstract (sommario):
In this paper, I draw an analogy between the use of electricity by electric eels (Electrophorus electricus) to paralyze prey muscles and the use of venoms that paralyze prey by disrupting the neuromuscular junction. The eel’s strategy depends on the recently discovered ability of eels to activate prey motor neuron efferents with high-voltage pulses. Usually, eels use high voltage to cause brief, whole-body tetanus, thus preventing escape while swallowing prey whole. However, when eels struggle with large prey, or with prey held precariously, they often curl to bring their tail to the opposite side. This more than doubles the strength of the electric field within shocked prey, ensuring maximal stimulation of motor neuron efferents. Eels then deliver repeated volleys of high-voltage pulses at a rate of approximately 100 Hz. This causes muscle fatigue that attenuates prey movement, thus preventing both escape and defense while the eel manipulates and swallows the helpless animal. Presumably, the evolution of enough electrical power to remotely activate ion channels in prey efferents sets the stage for the selection of eel behaviors that functionally “poison” prey muscles.
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Catania, Kenneth C. "Electric Eels Wield a Functional Venom Analogue". Toxins 13, n. 1 (10 gennaio 2021): 48. http://dx.doi.org/10.3390/toxins13010048.
Testo completoAbstract (sommario):
In this paper, I draw an analogy between the use of electricity by electric eels (Electrophorus electricus) to paralyze prey muscles and the use of venoms that paralyze prey by disrupting the neuromuscular junction. The eel’s strategy depends on the recently discovered ability of eels to activate prey motor neuron efferents with high-voltage pulses. Usually, eels use high voltage to cause brief, whole-body tetanus, thus preventing escape while swallowing prey whole. However, when eels struggle with large prey, or with prey held precariously, they often curl to bring their tail to the opposite side. This more than doubles the strength of the electric field within shocked prey, ensuring maximal stimulation of motor neuron efferents. Eels then deliver repeated volleys of high-voltage pulses at a rate of approximately 100 Hz. This causes muscle fatigue that attenuates prey movement, thus preventing both escape and defense while the eel manipulates and swallows the helpless animal. Presumably, the evolution of enough electrical power to remotely activate ion channels in prey efferents sets the stage for the selection of eel behaviors that functionally “poison” prey muscles.
7
Shuai, Fangmin, Xinhui Li, Wanling Yang, Weitao Chen e Sovan Lek. "Habitat use of the Japanese eel (Anguilla japonica) and marbled eel (Anguilla marmorata) in the large subtropical Pearl River". Annales de Limnologie - International Journal of Limnology 57 (2021): 8. http://dx.doi.org/10.1051/limn/2021001.
Testo completoAbstract (sommario):
Anguilla spp. are catadromous fish and with a high economic value in Asia. The Pearl River is the largest river in southern China and is an important area for wild populations of Anguilla spp. However, until now, there has been little research on the eel's population structure and habitat use in the Pearl River. This study analyzed the population structure and habitat use characteristics of the Japanese eel (Anguilla japonica) and the marbled eel (Anguilla marmorata) in the Pearl River based on data collected from 2015 to 2018. A total of 181 Japanese eels and 56 marbled eels were collected, over half of which were middle-sized eels between 255 and 600 mm in length. Although they are sister species, Japanese eels mainly inhabit complex river habitats characterized by high river fractals and coefficients of fluvial facies, while marbled eels mainly inhabit wider and deeper river sections. The impact of physical environmental factors (such as river fractals, coefficients of fluvial facies and river width) on the distribution of these two species is greater than the impact of small-scale water quality environmental factors (such as DO concentration, temperature and clarity). The results of this study showed that wild Anguilla spp. resources in the Pearl River were extremely low and there was an urgent need for conservation and management of eel resources in south China.
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Barić, Oliver, Tena Radočaj, Alexis Conides, Nevena Kitanović, Jurica Jug-Dujaković e Ana Gavrilović. "Functional Morphology as an Indicator of European Eel Population Status". Diversity 15, n. 12 (17 dicembre 2023): 1223. http://dx.doi.org/10.3390/d15121223.
Testo completoAbstract (sommario):
In the area of the Neretva delta in the eastern Adriatic, where the European eel, Anguilla anguilla (Linnaeus, 1758) has been traditionally fished for centuries, a decline in its population has been observed, as in most of Europe. Despite several studies, systematic monitoring was not performed, and the causes of population decline are attributed to anthropogenic stressors, mainly overfishing and interventions that disrupt the migration. With the stock at a low level, there is a need for a detailed assessment of biological data and the determination of the “zero state” of the eel population in the areas where monitoring was not previously performed, such as the Neretva delta. This data would serve as a basis for the development of an appropriate monitoring and eel management plan. One of the under-researched aspects is still the eel’s morphology, which is closely related to all basic life functions. The aim of this work was to analyze in detail the morphological parameters of yellow and silver eels from the mouth of the Neretva River in different seasons and the relationships between the measured morphometric parameters and physiological indicators and to compare them with previously published results for different life stages across Europe. The samples were collected during spring, summer and autumn of 2021, and winter of 2022. Yellow eels were present in the catch throughout the sampling period, while silver eels were caught in the autumn and winter. Yellow and silver eels were significantly different regarding 22 morphometric measures that were analyzed. Isometric growth was recorded for yellow eels in the spring and autumn of 2021, and positive allometric growth was recorded for yellow eels in the summer and silver eels in the autumn of 2021 and winter of 2022. PCA showed that the main factor that separates the eels grouped by life stage in different seasons is the intestine length (IL), whereas the rest of the factors (weight—W; intestine weight—IW; liver weight—LW; and total length—TL) affect the groupings almost equally. Seasonal averages of the condition factor (CF) for yellow and silver eels did not differ statistically. Three indicators were used to describe intestine morphology: relative gut weight (RGW), relative gut length (RGL), and Zihler’s index (ZHI); and the only statistically significant difference between yellow and silver eels was recorded for the RGW. The hepatosomatic index (HSI) was significantly different between silver eels in winter and yellow eels in spring. In addition to supplementing the already known facts, this paper provides new information on the functional morphology of the European eel. Monitoring of these characteristics is crucial for management of the European eel fisheries as they are directly related to functional performance and affect the ability to maintain sustainable populations in anthropogenically altered environments.
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MÜLLER, ULRIKE K., JORIS SMIT, EIZE J. STAMHUIS e JOHN J. VIDELER. "HOW THE BODY CONTRIBUTES TO THE WAKE IN UNDULATORY FISH SWIMMING". Journal of Experimental Biology 204, n. 16 (15 agosto 2001): 2751–62. http://dx.doi.org/10.1242/jeb.204.16.2751.
Testo completoAbstract (sommario):
SUMMARY 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 1.5Ls-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.
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Williams, Alan, Deborah Osterhage, Franziska Althaus, Timothy Ryan, Mark Green e John Pogonoski. "A Very Large Spawning Aggregation of a Deep-Sea Eel: Magnitude and Status". Journal of Marine Science and Engineering 9, n. 7 (30 giugno 2021): 723. http://dx.doi.org/10.3390/jmse9070723.
Testo completoAbstract (sommario):
Multiple lines of evidence substantiate the existence of a very large aggregation of the basketwork eel, Diastobranchus capensis, on the small (3 km2) Patience Seamount off southeast Australia. The aggregation appears to be present year-round, but largest in the austral autumn when composed of spawning eels. Twenty eels caught in April 2015 (14 female, 6 male) were all in advanced stages of spawning condition. The eel’s abundance in the aggregation was very high as measured at seamount, local and regional scales. Hydroacoustic measurement of the spawning aggregation’s dimensions (~100 × 1000 m) and conservative counts of 100 s of eels along camera transects of ~1000–2000 m length indicate 10,000 s individual eels may have been present. The absence of other known spawning locations indicates the Patience Seamount is a regional-scale spatial anchor for spawning. The aggregation was protected in a marine park in 2007 following a decades-long impact from bottom trawling, indicating that the population can be expected to stabilise and recover. Monitoring the aggregation’s status, and validating seasonal spawning, provide important opportunities to examine conservation-led recovery in the deep sea as part of Australia’s new national strategy of Monitoring, Evaluation, Reporting and Improvement (MERI) for conservation values within marine parks.
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Catania, Kenneth C. "Electrical Potential of Leaping Eels". Brain, Behavior and Evolution 89, n. 4 (2017): 262–73. http://dx.doi.org/10.1159/000475743.
Testo completoAbstract (sommario):
When approached by a large, partially submerged conductor, electric eels (Electrophorus electricus) will often defend themselves by leaping from the water to directly shock the threat. Presumably, the conductor is interpreted as an approaching terrestrial or semiaquatic animal. In the course of this defensive behavior, eels first make direct contact with their lower jaw and then rapidly emerge from the water, ascending the conductor while discharging high-voltage volleys. In this study, the equivalent circuit that develops during this behavior was proposed and investigated. First, the electromotive force and internal resistance of four electric eels were determined. These values were then used to estimate the resistance of the water volume between the eel and the conductor by making direct measurements of current with the eel and water in the circuit. The resistance of the return path from the eel's lower jaw to the main body of water was then determined, based on voltage recordings, for each electric eel at the height of the defensive leap. Finally, the addition of a hypothetical target for the leaping defense was considered as part of the circuit. The results suggest the defensive behavior efficiently directs electrical current through the threat, producing an aversive and deterring experience by activating afferents in potential predators.
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Pereira, Luís, Ana Catarina Braga, Ana Moura e Carlos Antunes. "PREVALENCE OF THE Anguillicola crassus PARASITE IN THE INTERNATIONAL MINHO RIVER". ENVIRONMENTAL SMOKE, Special Issue (31 marzo 2022): 64–74. http://dx.doi.org/10.32435/envsmoke/xibesymp.10.
Testo completoAbstract (sommario):
The European eel, Anguilla anguilla (Linnaeus, 1758), is vulnerable to infections by the parasitic nematode Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974, mainly in freshwater ecosystems. The eel is a bioindicator species due to its benthic behaviour, predator, and life cycle. The parasite feeds on blood from the eel's swim bladder, causing damage to the walls and deterioration of this organ, reducing energy reserves, and affecting its migratory capacity for reproduction. Eels were captured at different sampling points divided into 4 areas of the international section of the Minho River in the following time periods: 1995-96, 2008-2011 and 2017-2021, through fyke nets and electric fishing sampling techniques. The objectives of this work were to analyze the dispersion and prevalence of A. crassus in the Minho River basin over time, infection rates and the eels condition. The prevalence levels found reach values close to 75% in some sampled locations and 99% of eels shown pathological signs of swim bladder infection. The nematode dispersal area increased since the early 1990s when its presence in the Minho River was first recorded.
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Bakke, T. A., P. A. Jansen e L. P. Hansen. "Experimental transmission of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes, Monogenea) from the Atlantic salmon (Salmo salar) to the European eel (Anguilla anguilla)". Canadian Journal of Zoology 69, n. 3 (1 marzo 1991): 733–37. http://dx.doi.org/10.1139/z91-105.
Testo completoAbstract (sommario):
Laboratory experiments were designed as follows in an attempt to evaluate the potential importance of eels in dispersal of Gyrodactylus salaris: exposure of uninfected eels to infected salmon; exposure of infected eels to uninfected salmon; exposure of uninfected eels to infected eels; indirect infection of uninfected eels; parasite transmission preference, using "two-choice" host tests; and parasite survival on eels following their isolation. Gyrodactylus salaris was found to be transmissible from salmon to eels, and vice versa, both at 4 and 13 °C. Eel to eel transfer of G. salaris was also demonstrated, as was infection of fish from the bottom of the tank. Transmission of G. salaris to eels also occurred in the "two-choice" host tests. Transmission rate was positively correlated with water temperature and transmission was more frequent from dead than living infected salmon. The maximum duration of infection on eels was 8 days. The transfer of infection to eels is thought to parallel events in nature and forms part of the dispersal mechanism of G. salaris.
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Tsuchida, Takamasa, e Yoshio Takei. "Effects of homologous atrial natriuretic peptide on drinking and plasma ANG II level in eels". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 275, n. 5 (1 novembre 1998): R1605—R1610. http://dx.doi.org/10.1152/ajpregu.1998.275.5.r1605.
Testo completoAbstract (sommario):
The effects of eel atrial natriuretic peptide (ANP) on drinking were investigated in eels adapted to freshwater (FW) or seawater (SW) or in FW eels whose drinking was stimulated by a 2-ml hemorrhage. An intra-arterial infusion of ANP (0.3–3.0 pmol ⋅ kg−1 ⋅ min−1), which increased plasma ANP level 1.5- to 20-fold, inhibited drinking dose dependently in all groups of eels. The drinking rate recovered to the level before ANP infusion within 2 h after infusate was replaced by saline. The inhibition at 3.0 pmol ⋅ kg−1 ⋅ min−1was profound in FW eels and hemorrhaged FW eels, whereas significant drinking still remained after inhibition in SW eels. Plasma ANG II concentration also decreased dose dependently during ANP infusion and recovered to the initial level after saline infusion in all groups of eels. The decrease at 3.0 pmol ⋅ kg−1 ⋅ min−1was large in FW eels and hemorrhaged FW eels compared with that of SW eels. Thus the changes in drinking rate and plasma ANG II level were parallel during ANP infusion. Plasma sodium concentration and osmolality decreased during ANP infusion in SW and FW eels, and they were restored after saline infusion. In hemorrhaged FW eels, however, ANP infusion did not alter plasma sodium concentration and osmolality. Hematocrit did not change during ANP infusion in any group of eels. Collectively, ANP infusion at physiological doses decreased drinking rate and plasma ANG II concentration in parallel in both FW and SW eels. It remains undetermined whether the inhibition of drinking is caused by direct action of ANP or through inhibition of ANG II, which is known as a potent dipsogen in all vertebrate species, including eels.
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Sasai, Seiji, Toyoji Kaneko, Sanae Hasegawa e Katsumi Tsukamoto. "Morphological alteration in two types of gill chloride cells in Japanese eels (Anguilla japonica) during catadromous migration". Canadian Journal of Zoology 76, n. 8 (1 agosto 1998): 1480–87. http://dx.doi.org/10.1139/z98-072.
Testo completoAbstract (sommario):
Gill chloride cell morphology and Na+,K+-ATPase activity were examined in cultured Japanese eels (Anguilla japonica) acclimated to fresh water (FW) or seawater (SW), and in yellow and silver eels caught in wild stocks. Gill Na+,K+-ATPase activity was higher in SW-acclimated cultured eels than in FW eels. Chloride cells were detected in both filament and lamellar epithelia by immunocytochemical staining using anti-Na+,K+-ATPase serum. The filament chloride cells were more abundant and larger in SW eels than in FW eels, whereas there was no apparent difference in lamellar chloride cells. In wild-caught eels, gill Na+,K+-ATPase activity increased as they developed from yellow to silver eels. Filament chloride cells in silver eels were more active than those in yellow eels. In contrast, lamellar chloride cells, which were frequently observed in yellow eels, had decreased in number or disappeared in silver eels. These findings suggest that chloride cells in the filament are responsible for excretion of excess salt in hyperosmotic environments, and that lamellar chloride cells may play a significant role in hypoosmotic environments, presumably acting as sites of ion uptake. The excellent euryhalinity of the Japanese eel may be due, at least in part, to the presence of functionally different types of chloride cells. The activation of filament chloride cells in silver eels in FW, together with the increase in Na+,K+-ATPase activity, could be interpreted as a preadaptive response to forthcoming entry into SW.
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Kautsari, Neri, Husain Latuconsina e Ilham Zulfahmi. "Preliminary Study of Eels (Anguilla) in Sumbawa Island According to the Knowledge of Local Communities: Distributions, Pattern of Fishing, and Utilizations". Jurnal Ilmiah Perikanan dan Kelautan 15, n. 1 (27 gennaio 2023): 212–23. http://dx.doi.org/10.20473/jipk.v15i1.34905.
Testo completoAbstract (sommario):
Highlight Research The biodiversity, distribution and capture of eels on Sumbawa Island are traced through local community knowledge There are four types of eels in Sumbawa, namely marmorata, A. celebensis, A. interioris, A. bicolor Eels are found in rivers, dams, estuaries and rice fields Eel is not the main catch Eel fishing by the community is carried out because the hobby of fishing is not for livelihood In general, people do not know about eel conservation in Indonesia Abstract Eels are an important fishery resource in Indonesia, but information regarding distribution, fishing patterns and utilization has not been well documented in order for it to assist in the management of eel fisheries. One of the areas in Indonesia that uses eels is the Sumbawa Island community. The local community knowledge approach is an important for fisheries management, because it is an inherent component of fishery resources. This is preliminary study of eels in Sumbawa Island. This study aimed to examine the distribution, pattern of fishing, and utilization of eels from knowledge of local communities. Data were taken through in-depth interviews with 166 respondents. The study was conducted from November to December 2021. Interviews were conducted to obtain information and knowledge from local communities about eels (locations where they were eels found, fishing gear used, time, season and, utilization of eel, and community knowledge regarding its protection status). The results showed that the eels are found in dams, rivers, and estuaries. Most eels were caught from November to December in rainy season. Most people catch eels out of a hobby. Fishing rods and stuns are the two main fishing tools used to catch eels. There are three types of eel utilization, namely (1) consumed, (2) distributed to family and neighbors, and (3) marketed. Respondents (83.64%) did not know about the limited protection for several species of eels.
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Feunteun, Eric, Anthony Acou, Pascal Laffaille e Antoine Legault. "European eel (Anguilla anguilla): prediction of spawner escapement from continental population parameters". Canadian Journal of Fisheries and Aquatic Sciences 57, n. 8 (1 agosto 2000): 1627–35. http://dx.doi.org/10.1139/f00-096.
Testo completoAbstract (sommario):
This paper describes the assessment of silver European eel (Anguilla anguilla) escapement based on a "sedentary" population fraction analysis in a 60-km2 watershed of northern Brittany (France). Downstream migration fluxes were monitored using eel traps and related to environmental factors. Intensive electrofishing and fyke-net fishing were conducted to assess eel biomass, densities, and population structure. A total of 564 eels, including 81 silver eels, were PIT tagged. In 1996, 616 eels were caught in the catchment including 68 silver eels (11%). During the following downstream migration period, 12 of the PIT-tagged silver eels, among a total of 678, were recaptured in the downstream traps. Seven were recaptured in the catchment in 1997. It was shown that (i) only about 20% of the silver eels present in the catchment emigrated during the following year, (ii) 12% stayed in the catchment including two (3.4%) that recovered yellow eel characteristics, and (iii) the other eels either died or settled in the catchment but were not recaptured. It was also estimated that 2% (650 eels) of the population (34 000 eels) among 3000 silver eels considered "emigration candidates" emigrated each year,.
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Barreto, Rodrigo Egydio, Maria Fernanda Coelho Junqueira, Tan Tjui-Yeuw e Gilson Luiz Volpato. "Spatial choice is biased by chemical cues from conspecifics in the speckeled worm eel Myrophis punctatus". Neotropical Ichthyology 8, n. 4 (15 ottobre 2010): 899–902. http://dx.doi.org/10.1590/s1679-62252010005000011.
Testo completoAbstract (sommario):
The speckeld worm eel Myrophis punctatus lives in high-densities assemblages, and usually digs through, or lies on the substrate. These behaviours could lead to chemical marks on the substrate and could modulate the spatial distribution in this species. We tested the hypothesis that the spatial choice of the speckled worm eel is modulated by the presence of conspecific odour on the substrate. Here, we showed that the speckled worm eel avoids the substrate area containing the conspecific odour, indicating that this chemical cue modulates the eel's spatial decision. The eels clearly detected the conspecific's odour. This perception might indicate the presence of conspecifics into the substrate. Since the eels avoided an area containing conspecific odour, we suggest this may be a response that avoids the consequences of invading a resident-animal's territory.
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Parker, Steven J., e James D. McCleave. "Selective Tidal Stream Transport by American Eels During Homing Movements and Estuarine Migration". Journal of the Marine Biological Association of the United Kingdom 77, n. 3 (agosto 1997): 871–89. http://dx.doi.org/10.1017/s0025315400036237.
Testo completoAbstract (sommario):
Behaviour during homing movements and downstream migration of yellow- and silver-phase American eels (Anguilla rostrata) was observed using continuous ultrasonic telemetry in a tidal estuary. Homing subadult (yellow-phase) eels, non-displaced yellow-phase eels and adult (silver-phase) eels all used tidal currents as a transport mechanism (‘selective tidal stream transport’) and possibly as a means of orienting and moving in an appropriate direction. Yellow-phase eels displaced up the estuary and migrating silver-phase eels moved mostly at night and during ebbing tides. Yellow-phase eels displaced down the estuary moved mainly during flooding tides both day and night. Non-displaced eels used selective tidal stream transport to make long, round trip excursions and to move about their home range. Eels were at or near the surface during most of their movements, but were also vertically active, diving transiently to mid-water or to the bottom. During movements, the eels tended to drift with the current, or to swim slowly in the direction of the current. Although they used the tidal currents effectively as a transport mechanism, they were not precise in timing their movements to maximize transport on each tide. This study demonstrates that both yellow- and silver-phase eels use selective tidal stream transport during movements in tidal habitats and excludes some cues previously proposed to regulate the behaviour.
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Indrawati, Ayuningtyas, Putri Sapira Ibrahim, Fione Yukita Yalindua, Wanwan Kurniawan, Siti Aisyah, Sutrisno Anggoro e Suradi Wijaya Saputra. "Species Composition and Inshore Migration of the Tropical Glass Eels (<i>Anguilla</i> spp.) Recruiting to the Jali River, Purworejo Regency". Journal of Tropical Biodiversity and Biotechnology 9, n. 2 (19 aprile 2024): 82880. http://dx.doi.org/10.22146/jtbb.82880.
Testo completoAbstract (sommario):
Purworejo Regency is located in the south coast of Java where rivers flow into the Indian Ocean. The Jali River in Purworejo becomes a migration route for eels where juvenile eels (glass eels) move from the ocean to freshwater passing through the estuary. During migration, glass eels will make efforts to survive, one of which is to manage their osmotic pressure (osmolarity). With regards to those, a study on the upstream migration of glass eels in Jali River was carried out. Glass eels samplings were conducted using hand-held lift nets at the new moon phase, from 20:00 pm to 4:00 am. Sampling stations included the estuary, a branch river, and below the dam. The osmolarity of both glass eels and media (river water) were measured. Furthermore, the chemical and physical parameters of the waters as the natural habitat for glass eels were also measured. Glass eel samples were then identified to species level. The results showed that glass eels entering the Jali River consisted of Anguilla bicolor bicolor and Anguilla nebulosa nebulosa with the former being the most common. Total length of glass eels ranged between 44.10 to 69.70 mm with total weights 0.08 to 0.54 g. Glass eel migration has a close relation with surface current and tide. The osmotic work level (OWL) of glass eels approaches 0.34 mOsm/l H2O which is close to iso-osmotic. This happened at salinity 0 o/oo so that the glass eels migrate to fresh water which has a lower salinity to achieve iso-osmotic condition.
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Kaifu, Kenzo, Hikaru Itakura, Yosuke Amano, Kotaro Shirai, Kazuki Yokouchi, Ryoshiro Wakiya, Naoko Murakami-Sugihara, Izumi Washitani e Takashi Yada. "Discrimination of wild and cultured Japanese eels based on otolith stable isotope ratios". ICES Journal of Marine Science 75, n. 2 (15 settembre 2017): 719–26. http://dx.doi.org/10.1093/icesjms/fsx173.
Testo completoAbstract (sommario):
Abstract We successfully discriminated wild and cultured anguillid eels without artificial tagging. For the purpose of population restoration of anguillid eels, stocking has been widely conducted in the European Union (EU) and Japan, although the net benefits of stocking remain unclear. To evaluate the effectiveness of eel stocking for population restoration, the survival, growth, escapement, and reproduction of stocked eels should be tracked. In this study, we explored the potential of using otolith oxygen and carbon stable isotope ratios as a natural tag to discriminate between wild and cultured eels, because cultured eels are often stocked into natural rivers and lakes. A discrimination model was developed based on wild (n = 95) and cultured (n = 314) Japanese eels as a training dataset. The results of accuracy estimation based on leave-one-out cross-validation were 96.8%. We then tested the applicability of the model to stocked–recaptured eels (n = 20); 100.0% were successfully identified as cultured eels, indicating that these eels spend their early continental phase in aquaculture ponds before stocking. This method could be widely applied to assess the effectiveness of eel stocking by determining the proportion of stocked eels among those captured from rivers, coastal areas, or spawning grounds.
22
Dutil, J. D., M. Michaud e A. Giroux. "Seasonal and diel patterns of stream invasion by American eels (Anguilla rostrata) in the northern Gulf of St. Lawrence". Canadian Journal of Zoology 67, n. 1 (1 gennaio 1989): 182–88. http://dx.doi.org/10.1139/z89-024.
Testo completoAbstract (sommario):
Seasonal and diel patterns of stream invasion by American eels (Anguilla rostrata) were monitored in a small stream located on the north shore of the Gulf of St. Lawrence from 1981 to 1985. Glass eels and elvers migrated from the sea in late June and July. Glass eels made up only a small percentage of the migrants. Pigmentation progressed quickly in the estuary, but elvers grew very slowly. Migration from the estuary and through the lower reaches of the stream was slow; no glass eels or elvers occurred at a station located only 4 km from saltwater. Juvenile eels reached that station in their second summer of stream residence. Juvenile eels migrated in July and August. They ranged from 70 to 250 mm in length and included more than one age-class. Those less than 100 mm in length were most numerous. Relative abundance of glass eels and elvers decreased in the estuary from 1981 to 1985. This coincided with a decrease in the proportion of smaller sized eels in the stream migration over the same period. Juvenile eels migrated progressively later in summer as the proportion of smaller sized eels decreased. Stream migration was nocturnal. Movements mainly occurred between 21:00 and 23:00. The relationship between glass eel and elver abundance in the estuary and juvenile eel abundance in the stream 1 and 2 years later was not clear.
23
Shuai, Fangmin, Jie Li, Shunchao Yu e Jian Yang. "Temporal Pattern of the Occurrence of Japanese Glass Eels (Anguilla japonica) in the Pearl River Estuary". Fishes 8, n. 5 (11 maggio 2023): 256. http://dx.doi.org/10.3390/fishes8050256.
Testo completoAbstract (sommario):
Japanese eels (Anguilla japonica) are a typical migratory fish species with high commercial importance. The Pearl River estuary in southern China is an important natural growing ground for Japanese glass eels, but limited information on Japanese glass eel population characteristics is available, despite their ecological importance. In this paper, we examined the annual patterns of the occurrence of Japanese glass eels in the Pearl River estuary from 2011 to 2022. The most frequently occurring Japanese glass eel’s total length is 5.3 cm. The collecting period extended from December to February, and the collection catch-per-unit-effort (CPUE) decreased significantly from 2011 to 2022. The generalized linear model (GLM) indicated that daily changes in Japanese glass eel collection were significantly affected by tidal range, water temperature, and lunar distance. The catch peak appeared when the tidal range rose to 1.7 m, and the water temperature dropped below 8 °C on the full moon days. Overall CPUE analysis showed no significant periodic and inter-annual variability in the period 2011–2022, with the ARIMA model suggesting that the CPUE is expected to remain stable but low in the coming years (2023–2026), although recruitment ultimately depends on the overall spawning stock.
24
Barbin, Gayle P. "The role of olfaction in homing and estuarine migratory behavior of yellow-phase American eels". Canadian Journal of Fisheries and Aquatic Sciences 55, n. 3 (1 marzo 1998): 564–75. http://dx.doi.org/10.1139/f97-274.
Testo completoAbstract (sommario):
The role of olfaction in homing migrations of American eels (Anguilla rostrata) was examined in the Penobscot Estuary, Maine, U.S.A. Ultrasonic telemetry was used to track continuously (65 ± 12 h) 16 yellow eels displaced from a capture site. Four eels were not treated, eight rendered anosmic, and four rendered partially anosmic. All normal, only three anosmic, and two partially anosmic eels homed. Normal eels expressed a singular behavioral pattern, selective tidal stream transport (STST). STST was also displayed by three anosmic eels and one partially anosmic eel. Three alternative behavioral patterns ("sporadic vertical excursions," "sloshing," and "directed swimming") were displayed by the remainder of the anosmic and partially anosmic eels. Eels that displayed STST used the water column differently (moving at depths shallower than the thermocline, halocline, and pycnocline) from those that displayed other behaviors. Olfaction seems to be important for discrimination of the appropriate tide for transport and location of a home site but is not the only orientational mechanism used in estuaries. Mechanisms used to detect rates of change of water mass characteristics are probably important for guidance of estuarine migrations.
25
Hanke, Gavin F., e Steven M. Roias. "First Specimens of the Marine Eels Venefica ocella and V. tentaculata (Nettastomatidae) from British Columbia". Canadian Field-Naturalist 126, n. 3 (23 gennaio 2013): 210. http://dx.doi.org/10.22621/cfn.v126i3.1362.
Testo completoAbstract (sommario):
Until recently, only the following seven species of marine eels were known to exist in waters off British Columbia (based on literature sources and museum records): Nemichthys scolopaceus, and Avocettina infans (Nemichthyidae, snipe eels), Xenomystax atrarius (Congridae, conger eels), Serrivomer jesperseni (Serrivomeridae, sawtooth eels), Cyema atrum (Cyematidae, bobtail eels), Synaphobranchus affinis (Synaphobranchidae, cutthroat eels), and Thalassenchelys coheni (Colocongridae, worm eels). Histiobranchus bathybius (also in the Synaphobranchidae) is expected to occur in British Columbia, since its range extends from Mexico to Alaska. Recent surveys to determine the viability of crab fisheries facilitated the collection of non-game fishes from by-catch in bottom-trawl samples. Several eels were collected between 2004 and 2006, and they were originally identified as Serrivomer jesperseni (Serrivomeridae). Re-examination of these specimens indicates that they all are duckbill eels (Nettastomatidae), the first records of this family north of 45°39'N along the North American Pacific coast. Both Venefica ocella and V. tentaculata are represented, with V. ocella found farther north than V. tentaculata. All British Columbia specimens are housed at the Royal British Columbia Museum. The collection of new deep-water species in British Columbia reinforces the value of survey sampling to improve our knowledge of biodiversity.
26
Budiharjo, Agung, Tjut Sugandawaty Djohan, Djumanto Djumanto e Jusup Subagja. "UMUR GLAS EEL (Anguilla spp.) YANG MASUK MUARA SUNGAI PROGO, YOGYAKARTA". Berkala Penelitian Hayati 14, n. 2 (30 giugno 2009): 179–83. http://dx.doi.org/10.23869/bphjbr.14.2.200910.
Testo completoAbstract (sommario):
The leptocephalus drift with sea currents and moving from spawning area into coastal area near mouth of Progo River. In the coastal area, leptocephalus metamorfosed into glass eel, after that glass eel migrated to river. The aims of this research were to estimate glass eels age and predict hatching dates. Glass eels sampled on new moon during Februari 2007–Mei 2009 at mouth of Progo River. Glass eel ages estimated using their otolith microstructure. Hatching dates predicted with back calculation of glass eels age. We collected 1.082 glass eels. The ages of glass eel at recruit ranged from 58 to 190 days, and divided into 5 age groups. Glass eels are migrated to river hatched on new moon from July to January. Glass eels are migrated to river during October–January hatched during July–October. Glass eels are migrated to river during February–Juny hatched during November – January.
27
Payne, Gregory W., e Bruce B. Collette. "Novel Eels". BioScience 40, n. 2 (febbraio 1990): 76. http://dx.doi.org/10.2307/1311335.
Testo completo
28
Cowgill, M. A. "Sold Eels". Colorado Review 47, n. 2 (2020): 46–47. http://dx.doi.org/10.1353/col.2020.0069.
Testo completo
29
JACOBY, MITCH. "ULTRAFAST EELS". Chemical & Engineering News 87, n. 28 (13 luglio 2009): 9. http://dx.doi.org/10.1021/cen-v087n028.p009.
Testo completo
30
Williamson, Michael J., Charlotte Pike, Matthew Gollock, David M. P. Jacoby e Adam T. Piper. "Anguillid eels". Current Biology 33, n. 17 (settembre 2023): R888—R893. http://dx.doi.org/10.1016/j.cub.2023.07.044.
Testo completo
31
Helfman, Gene S. "Diel Distribution and Activity of American Eels (Anguilla rostrata) in a Cave-Spring". Canadian Journal of Fisheries and Aquatic Sciences 43, n. 8 (1 agosto 1986): 1595–605. http://dx.doi.org/10.1139/f86-198.
Testo completoAbstract (sommario):
American eels (Anguilla rostrata) in a Florida cave-spring (total population [Formula: see text] 142 eels, density [Formula: see text] 0.03 eels/m2) showed distinctive day versus night differences in distribution and activity. Larger eels occurred deeper at all times. Eels were diurnally quiescent, nocturnally active, and changed over between behavior modes roughly at dusk and dawn, although considerable variability existed in timing of changeover. Changeover at dusk involved movement from deeper regions of low food to shallower regions of high food concentration, with smaller eels more likely to migrate. Changing light levels apparently determined onset and cessation of activity, with an inhibitory threshold of 10–100 lx influencing movement between deep and shallow regions. An endogenous rhythm and hunger may have also affected activity patterns.
32
Arai, Takaomi, Aya Kotake e Madoka Ohji. "Variation in migratory history of Japanese eels, Anguilla japonica, collected in the northernmost part of its distribution". Journal of the Marine Biological Association of the United Kingdom 88, n. 5 (25 luglio 2008): 1075–80. http://dx.doi.org/10.1017/s0025315408001756.
Testo completoAbstract (sommario):
In order to examine the variation of migratory histories in the Japanese eel, Anguilla japonica, we measured otolith strontium (Sr) and calcium (Ca) concentrations by X-ray electron microprobe analysis in A. japonica collected in a coastal brackish water lake in the northernmost part of its distribution. Two migratory types that were categorized as river eels and estuarine eels were found. Estuarine eels were dominant (85%), while ordinary diadromous eels that had entered the freshwater habitat made up only 15% of the population. The low proportion of river eels suggested that the estuarine eels that inhabit the nearby coastal areas might make a larger reproductive contribution to the next generation in this area. There was no significant difference in growth between the river and estuarine eels, which suggested that the limited carrying capacity of the adjacent river and geographical features might be more effective in determining the habitat use of the Japanese eel than the genetic feature and food abundance at the northern edge of its distribution.
33
Honda, Satoshi, Dina Muthmainnah, Ni Komang Suryati, Dian Oktaviani, Somboon Siriraksophon, Taweekiet Amornpiyakrit e Budi Iskandar Prisantoso. "CURRENT STATUS AND PROBLEMS OF THE CATCH STATISTICS ON ANGUILLID EEL FISHERY IN INDONESIA". Marine Research in Indonesia 41, n. 1 (31 maggio 2016): 1–14. http://dx.doi.org/10.14203/mri.v41i1.94.
Testo completoAbstract (sommario):
To compensate the decline of the populations of temperate anguillid eels, tropical anguillid eels become getting attention of East Asian eel market in recent years. Many eel farms have been established in Java Island to culture tropical anguillid eels intending to export the products to East Asia. Since eel farming is reliant on wild-caught anguillid eels such as glass eels, elvers and yellow eels, these eel seeds have been captured in various places in Indonesia. However, it is still unknown that how much of tropical anguillid eels are caught as seeds for eel farming. This study showed two different patterns of the commodity chains of eel seeds from both Sukabumi Regency and Bengkulu Province to the eel farms in Java Island. Official catch statistics on anguillid eels found in both Sukabumi Regency and Bengkulu Province were also analyzed on their features and problems underlied. Considering the sustainable use of anguillid eel resources and critical stances on exploitation of eel seeds from all over the world, the Indonesian government should take an immediate action for developing the national catch statistics on anguillid eel fishery as soon as possible.
34
Béguer-Pon, Mélanie, Martin Castonguay, José Benchetrit, Daniel Hatin, Guy Verreault, Yves Mailhot, Valérie Tremblay et al. "Large-scale migration patterns of silver American eels from the St. Lawrence River to the Gulf of St. Lawrence using acoustic telemetry". Canadian Journal of Fisheries and Aquatic Sciences 71, n. 10 (ottobre 2014): 1579–92. http://dx.doi.org/10.1139/cjfas-2013-0217.
Testo completoAbstract (sommario):
Downstream migration of silver American eels (Anguilla rostrata) from the St. Lawrence system was examined using acoustic telemetry. One hundred and thirty six silver American eels were tagged, and their passage was recorded using fixed acoustic arrays covering a 420 km distance along the St. Lawrence River and Estuary. Eighty-nine percent of the tagged eels were detected. All migrant eels (111) exhibited unidirectional and downstream movements, but the migration was not completed in one continuous direct movement. High individual variability in migratory longitudinal profiles was documented as well as in individual speed with no apparent relation to river discharge or morphological traits. Migration speed increased over the season. Our observations demonstrated that migrating silver American eels are largely nocturnal and demonstrated the use of nocturnal, ebb tide transport to leave the estuary. With 44 additional eels tagged and released in the maritime estuary, escapement of 180 silver American eels from the Gulf of St. Lawrence system was monitored along a 125 km acoustic line that entirely covered Cabot Strait in 2011. Surprisingly, only four of the tagged eels were recorded escaping the Gulf of St. Lawrence.
35
Warshafsky, Zoemma T., Troy D. Tuckey, Wolfgang K. Vogelbein, Robert J. Latour e Andrew R. Wargo. "Temporal, spatial, and biological variation of nematode epidemiology in American eels". Canadian Journal of Fisheries and Aquatic Sciences 76, n. 10 (ottobre 2019): 1808–18. http://dx.doi.org/10.1139/cjfas-2018-0136.
Testo completoAbstract (sommario):
American eels (Anguilla rostrata) are infected by the non-native parasitic nematode Anguillicoloides crassus, which can cause severe swim bladder damage. We investigated epidemiology of A. crassus to better understand its population-level effects on American eels. Nematode prevalence, abundance, and intensity and swim bladder damage were quantified in glass eels, elvers, and yellow eels from the lower Chesapeake Bay and related to season of capture, river system, and total length. Age-variant force-of-infection and disease-associated mortality were estimated using a three-state irreversible disease model, which assumes recovery is not possible. Results showed glass eels have very low infection prevalence and severity compared with elvers and yellow eels. Nematode abundance varied by season, river, and eel length, whereas swim bladder damage varied by season and eel length. Nematode abundance and swim bladder damage were weakly positively correlated. Force-of-infection, based on swim bladder damage, peaked at age 2, and disease-positive eels had an estimated lower annual survival probability of 0.76 compared with disease-negative eels. Full understanding of American eel population dynamics will require broader knowledge of cryptic disease-associated mortality throughout North America.
36
Ely, Taylor, Nathaniel Patten, Lewis C. Naisbett-Jones, Erin T. Spencer, Demian A. Willette e Peter B. Marko. "Molecular identification of critically endangered European eels (Anguilla anguilla) in US retail outlets". PeerJ 11 (6 febbraio 2023): e14531. http://dx.doi.org/10.7717/peerj.14531.
Testo completoAbstract (sommario):
The European eel (Anguilla anguilla) has declined by over 90% since the early 1980s and has been listed as critically endangered. Yet, despite strict export bans from the European Union, the European eel is still sold illegally in many countries. Efforts to monitor the trade of European eels have been primarily concentrated in Asian markets where concerningly high rates of European eel have been reported. Comparably fewer studies have assessed the identities of eel samples from the United States (US), despite the obvious implications for eel conservation. To address this knowledge gap, we purchased 137 eel products (134 freshwater eels and three saltwater eels) from grocers, sushi bars, and restaurants in nine states across the US from 2019 to 2021. Seven samples (5.2%) labeled as freshwater eels (or “unagi”) were identified as European eels using a combination of mitochondrial (cytochrome b) and nuclear (18S rRNA) restriction digestion assays, a fast and inexpensive molecular tool for seafood identification that can identify hybrids between European eels (A. anguilla) and American eels (A. rostrata). No hybrids between European and American eels were found and all seven samples identified with restriction digestion as European eels were confirmed by sequencing of cytochrome b and 18S rRNA. Frequency of European eels in US markets did not significantly correlate with state or retail type. Although illegal eel exports are likely reaching US consumers, the frequency of European eel samples in this study of the US market is much lower than found in other non-European countries.
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Itakura, Hikaru, e Ryoshiro Wakiya. "Habitat preference, movements and growth of giant mottled eels, Anguilla marmorata, in a small subtropical Amami-Oshima Island river". PeerJ 8 (3 novembre 2020): e10187. http://dx.doi.org/10.7717/peerj.10187.
Testo completoAbstract (sommario):
Although anguillid eel populations have decreased remarkably in recent decades, few detailed ecological studies have been conducted on tropical eels such as the giant mottled eel whose range extends across the whole Indo-Pacific. This species was studied throughout the entire 0.5 km mainstem reaches of Oganeku River on the subtropical Amami-Oshima Island of Japan over a two-year period using four sampling periods to understand its habitat preference, early life-stage dispersal process, movements, and annual growth using a mark-recapture experiment conducted with quantitative electrofishing. A total of 396 juvenile growth-phase A. marmorata eels were caught and tagged, with 48 individuals being recaptured at least once. Their density irrespective of size of eels was most strongly determined by distance from the river mouth, followed by riverbank type according to random forest models. Eel density decreased with increasing distance from the freshwater tidal limit located about 100–150 m from the river mouth. Eels preferred vegetated riverbanks, while they avoided those of concrete and sand. The density of small eels (total length: TL < 240 mm) was also associated with depth and velocity, with small eels tending to prefer riffle or run habitats. In contrast, large eels (TL ≥ 240 mm) were found in habitats of any depth and velocity. The TL of eels had a minimum peak at around the tidal limit, and it increased with increasing distance from the tidal limit. The observed density and size gradients of eels in relation to the distance from the river mouth suggested that A. marmorata initially recruited to freshwater tidal limit areas and then dispersed in both downstream and upstream directions. The growth rate of eels varied greatly among individuals that were at large for various periods of time and ranged from 0 to 163.2 mm/year (mean ± SD of 31.8 ± 31.0 mm/year). Of the recaptured eels, 52.1% were recaptured in a section that was different from the original capture section, and their mean ± SD distance travelled was 46.5 ± 72.5 m (median = 20 m). 47.9% of the eels were recaptured from the original section of capture (i.e., <10 m distances travelled), suggesting that they had strong fidelity to specific habitats with limited movements. The distance travelled of eels that had moved was greater for small eels (range = 10–380 m; mean ± SD = 84.4 ± 121.9 m) than large individuals (range = 10–120 m; mean ± SD = 30.9 ± 31.0 m), which indicates that the mobility of the eels declines as they grow. This is the first clear detailed documentation of the spatial distribution, growth, and movements of tropical eels in a small river system in relation to environmental conditions that provides an example of how future studies can be conducted in other areas to understand how conservation efforts can be most efficiently targeted for maximum success.
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Watanabe, Shigeru, e Kazutaka Shinozuka. "Spatial learning in Japanese eels (Anguilla japonica)". Animal Cognition 23, n. 1 (24 ottobre 2019): 233–36. http://dx.doi.org/10.1007/s10071-019-01320-y.
Testo completoAbstract (sommario):
Abstract Japanese eels (Anguilla japonica) were trained on a Morris-type spatial learning task. There were four tubes in a pool, but the eels could hide in only one of these. The eels learned the position of the open tube, and maintained their performance when the pool was rotated to remove possible intra-maze cues. The eels could not maintain their performance in a dark room, suggesting that spatial learning involved extra-maze visual cues. When the position of the open tube was randomly changed every day, the performance of the eels in finding the open tube did not improve.
39
Würtz, J., H. Taraschewski e B. Pelster. "Changes in gas composition in the swimbladder of the European eel (Anguilla anguilla) infected with Anguillicola crassus (Nematoda)". Parasitology 112, n. 2 (febbraio 1996): 233–38. http://dx.doi.org/10.1017/s003118200008481x.
Testo completoAbstract (sommario):
SummaryThe effect of Anguillicola crassus (Nematoda) on gas composition in the swimbladder of eels (Anguilla anguilla) was studied using mass spectrometry in feral eels from two German rivers and in experimentally infected eels. In both naturally and experimentally infected eels significant correlations were observed between the proportion of oxygen in the swimbladder and level of infection with Anguillicola crassus. In swimbladders of naturally infected feral eels the contribution of oxygen to swimbladder gas was reduced by 36–62·9% and in experimentally infected eels it was reduced by 11·4–57% compared to uninfected controls. The proportion of CO2 appeared to be lower in infected swimbladders compared to uninfected ones. However, this change was not significant. The findings are discussed in relation to an altered structure of the swimbladder wall due to the parasite.
40
NORTON, J., D. ROLLINSON e J. W. LEWIS. "Epidemiology ofAnguillicola crassusin the European eel (Anguilla anguilla) from two rivers in southern England". Parasitology 130, n. 6 (17 febbraio 2005): 679–86. http://dx.doi.org/10.1017/s0031182004007139.
Testo completoAbstract (sommario):
European eelsAnguilla anguillafrom the rivers Thames and Test, in the south of England, were examined between 2000 and 2003 for infection with the swim-bladder nematodeAnguillicola crassus. Since its introduction to Thames eels at tidal estuarine locations circa 1987,A. crassushas become established in non-tidal freshwater stretches upriver and data from these locations are reported for the first time. The prevalence of infection at Thames estuary locations was higher during 2000–2003 than for the period 1987–1992. By 2003, similar prevalences were observed at freshwater and estuarine locations, but infection intensities were significantly higher in freshwater. Eels from the river Test appear to have been recently colonized byA. crassus(circa 2000). Parasite population establishment within these eels was uncharacteristically slow during 2000–2001, with low prevalence and intensity of infection, and few gravid females during this period. By 2003, infection levels in Test eels were similar to those in Thames eels. The expansion of theA. crassuspopulation in Test eels has occurred in the absence of the paratenic host ruffeGymnocephalus cernuus, and at suboptimal pH for the survival and infectivity of free-living larvae. The epidemiology ofA. crassusin Test eels demonstrates that transmission ofA. crassusby ruffe is not required for high prevalence and intensity of infection in eels. However, the consistently low and atypical levels of infection in Test eels during 2000 and 2001 suggests that paratenic transmission by ruffe may provide a substantial contribution to the dynamics ofA. crassusin eels in the early years following introduction, by facilitating the rapid increase in prevalence and intensity ofA. crassusinfection that typically occurs during this time.
41
Nzau Matondo, Billy, François Fontaine, Olivier Detrait, Cathérine Poncelet, Stéphanie Vandresse, Patrice Orban, Justine Gelder et al. "Glass Eel Restocking Experiments in Typologically Different Upland Rivers: How Much Have We Learned about the Importance of Recipient Habitats?" Water 15, n. 17 (31 agosto 2023): 3133. http://dx.doi.org/10.3390/w15173133.
Testo completoAbstract (sommario):
The efficiency of glass eel restocking as a conservation measure to restore the altered local eel stocks has never been evaluated by integrating the dimension of typological diversity of freshwater habitats in eel recruitment performance in terms of the abundance, density, growth, silvering, survival, catchability and eel yields. Here, we used the electrofishing method during a 6-year study to catch eels, and the most appropriate Jolly–Seber model was applied to estimate the demographic parameters in open populations. We found that most eels were yellow eels in the growth phase with a low abundance (eels 3+: 2.8% and eels 5+: 7.1%) of silver eels, which were only males at the MII migrating phase. Eel recruitment performance varied between sector/river habitats. Restocked eels showed annually positive allometric growth type with good length increments and better condition factors. They have survived in almost all sectors with a survival rate > 0.810. Eels were more abundant and denser (maximum 0.128 individuals m−2) in one sector with a high quality of habitats offering optimal living conditions in terms of the protection against predators and water flow, settlement and food availability, as revealed by it having the highest eel yields. In contrast, no eels were found in two sectors whose habitats offered a high threat of predation, poor burial properties and insufficient protection against water flow. Sector/river habitats play a key role in the success of yellow eel production and certainly, over time, future genitor production. This study provides recommendations for the management of eels and their habitats during restocking aimed at the conservation of this threatened species.
42
Lennox, Robert J., Finn Økland, Hiromichi Mitamura, Steven J. Cooke e Eva B. Thorstad. "European eel Anguilla anguilla compromise speed for safety in the early marine spawning migration". ICES Journal of Marine Science 75, n. 6 (10 agosto 2018): 1984–91. http://dx.doi.org/10.1093/icesjms/fsy104.
Testo completoAbstract (sommario):
Abstract There are substantial benefits to potential fitness conferred to animals that undertake migrations. However, animals must make compromises to maximize survival and compensate for the risks associated with long-distance movement. European eel (Anguilla anguilla), a migratory catadromous fish, has undergone population declines owing to changes in marine and freshwater habitat and interactions with human infrastructure, instigating research to investigate the mechanisms controlling their migration. Yellow-phase European eels from the local River Opo and silver-phase European eels transplanted from River Imsa, Norway, were implanted with acoustic transmitters and released within a network of receiver stations in the Hardangerfjord, Norway. Silver-phase eels exhibited more movement within the array than yellow-phase eels, signifying the onset of migration. Silver-phase eels moved through the fjord nocturnally, arriving at gates predominantly at night. Eels had slower rates of migration than expected based on models predicting continuous movement, suggesting that movement ceased during daylight hours. Reduced net rates of travel supported the hypothesis that eels compromise speed for safety during the early marine migration by avoiding predators and not actively migrating during daylight. The silver eels were capable of directed movement towards the ocean and were not recorded by receivers in bays or dead ends. European eels must successfully transit this coastal zone, where their residence is prolonged because of the relatively slow speeds. These results suggest that the early marine phase of the European eel spawning migration be a focal period for European eel conservation efforts.
43
Jansen, Henrice M., Hendrik V. Winter, Maarten C. M. Bruijs e Harry J. G. Polman. "Just go with the flow? Route selection and mortality during downstream migration of silver eels in relation to river discharge". ICES Journal of Marine Science 64, n. 7 (1 ottobre 2007): 1437–43. http://dx.doi.org/10.1093/icesjms/fsm132.
Testo completoAbstract (sommario):
Abstract Jansen, H. M., Winter, H. V., Bruijs, M. C. M., and Polman, H. J. G. 2007. Just go with the flow? Route selection and mortality during downstream migration of silver eels in relation to river discharge. – ICES Journal of Marine Science, 64: 1437–1443. The European eel (Anguilla anguilla) has been in steep decline for several decades. Fisheries and hydropower-induced mortality presumably play an important role during the downstream migration of silver eels, and downstream-migrating silver eels must make various navigation and route-selection decisions to reach the sea. We examined the influence of river discharge on route selection of silver eels. To quantify the impact of hydropower and fisheries on silver eel mortality, radio-telemetry experiments were performed in the River Meuse in 2002 and 2004, surgically implanting 300 silver eels with Nedap-transponders. Route selection and passage behaviour near detection stations was assessed. Silver eels were distributed over the alternative migration routes in the river in proportion to the discharge until the silver eels reached the entrance to the turbines. The eels altered their behaviour when approaching the turbines of hydropower plants and showed stationary and recurrent behaviour. We discuss the consequences of this on route selection and mortality rates caused by hydropower facilities and fisheries.
44
Castro, Fernando C., e Vinayak P. Dravid. "Characterization of Lithium Ion Battery Materials with Valence Electron Energy-Loss Spectroscopy". Microscopy and Microanalysis 24, n. 3 (giugno 2018): 214–20. http://dx.doi.org/10.1017/s1431927618000302.
Testo completoAbstract (sommario):
AbstractCutting-edge research on materials for lithium ion batteries regularly focuses on nanoscale and atomic-scale phenomena. Electron energy-loss spectroscopy (EELS) is one of the most powerful ways of characterizing composition and aspects of the electronic structure of battery materials, particularly lithium and the transition metal mixed oxides found in the electrodes. However, the characteristic EELS signal from battery materials is challenging to analyze when there is strong overlap of spectral features, poor signal-to-background ratios, or thicker and uneven sample areas. A potential alternative or complementary approach comes from utilizing the valence EELS features (<20 eV loss) of battery materials. For example, the valence EELS features in LiCoO2 maintain higher jump ratios than the Li–K edge, most notably when spectra are collected with minimal acquisition times or from thick sample regions. EELS maps of these valence features give comparable results to the Li–K edge EELS maps of LiCoO2. With some spectral processing, the valence EELS maps more accurately highlight the morphology and distribution of LiCoO2 than the Li–K edge maps, especially in thicker sample regions. This approach is beneficial for cases where sample thickness or beam sensitivity limit EELS analysis, and could be used to minimize electron dosage and sample damage or contamination.
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Palstra, Arjan P., Ida van de Ven, Pauline Jéhannet, Leo Kruijt, Henk Schipper, William Swinkels e Leon T. N. Heinsbroek. "Human Chorionic Gonadotropin Enhancement of Early Maturation and Consequences for Reproductive Success of Feminized European Eel (Anguilla anguilla)". Fishes 8, n. 6 (25 maggio 2023): 281. http://dx.doi.org/10.3390/fishes8060281.
Testo completoAbstract (sommario):
To induce oocyte development, eels are weekly injected with salmon or carp pituitary extract (CPE). The weekly handling and hormone peaks result in inferior oocyte quality; therefore, alternative treatments that improve oocyte quality and reproductive success require investigation. The enhancement of early sexual maturation by a single injection with human chorionic gonadotropin (hCG), administered prior to CPE treatment, was investigated. Fifty feminized eels were subjected to simulated migration, after which eels received either a hCG or a sham injection. After two months, the hCG-treated eels showed an increase in eye size, gonadosomatic index (GSI), and plasma 11-ketotestosterone concentration, when compared with the sham-injected controls. The hCG-treated eels showed increases in oocyte diameter and lipid area, and in ovarian expression of aromatase (cyp19), follicle stimulating hormone receptor (fshr) and lipoprotein lipase (lpl). Yolk was present in the oocytes of the hCG-treated eels, not yet in the oocytes of the controls. The hCG-induced deposition of yolk may relate to early-life treatment with 17β-estradiol during feminization. hCG-treated eels required four CPE injections less to mature than the controls. hCG treatment may benefit reproductive success in feminized eels by initiating vitellogenesis and reducing the hypophysation period, although larvae were obtained from most females in both groups.
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Hunt, J. A., e D. B. Williams. "EELS detection limits". Proceedings, annual meeting, Electron Microscopy Society of America 50, n. 2 (agosto 1992): 1468–69. http://dx.doi.org/10.1017/s0424820100131978.
Testo completoAbstract (sommario):
Why determine detection limits? A natural question to ask about any quantitative technique, including EELS in the STEM, is “How little of <x> can be observed?” Detection limits serve as a guide to what problems are solvable and what are the best techniques to analyze specific systems, e.g., EELS vs. EDXS vs. SIMS, etc. The exercise of determining EELS detection limits provides a sobering reminder of sizable uncertainties of numerous EELS variables, e.g., cross-sections, analyzed volumes, interaction delocalization, etc. Minimizing detection limits require optimization of many issues of the field, such as beam size and energy spread, the spectrometer and detector, quantitation techniques and specimen preparation. Additionally, comparing obtainable detection limits with theoretical values allows assessment of the rate at which a major portion of the field of EELS is maturing. Such assessments provide useful clues to if and where further development work is justified.Traditional detection limit calculations. Typically there have been two types of detection limits discussed in EELS, the minimum detectable mass (MDM) and the minimum mass fraction (MMF).
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Rolvien, Tim, Florian Nagel, Petar Milovanovic, Sven Wuertz, Robert Percy Marshall, Anke Jeschke, Felix N. Schmidt et al. "How the European eel ( Anguilla anguilla ) loses its skeletal framework across lifetime". Proceedings of the Royal Society B: Biological Sciences 283, n. 1841 (26 ottobre 2016): 20161550. http://dx.doi.org/10.1098/rspb.2016.1550.
Testo completoAbstract (sommario):
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.
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Riyanto, Mochammad, Ai Siti Aminah, Wazir Mawardi e Ronny Irawan Wahju. "Response of Anguilla bicolor Glass Eel to Different Light Colors". Omni-Akuatika 19, n. 1 (24 luglio 2023): 61. http://dx.doi.org/10.20884/1.oa.2023.19.1.993.
Testo completoAbstract (sommario):
The response of eel fish (Anguilla bicolor) glass eel stadia to different light is fundamental knowledge for developing fishing methods and conserving fish resources. The study aimed to describe how glass eel fish react to different types of light. In the laboratory, glass eels were observed responding to red, blue, and white LED light versus no light as controls. Glass eels ranging in size from 4.0 to 6.1 cm and weighing up to 0.28 g were caught in the Pelabuhanratu estuary of the Cimandiri River. Observations were made for 31 days, beginning five days after the glass eel was captured. The Mann Whitney and Kruskal-Wallis tests were used to describe differences of the glass eel's response to light. Observations showed that glass eels responded more to dark zones with values above 80% when compared to zones given red, blue, and white LED light. The percentage of fish in red LED lights was 23±0.22% higher, with the number of fish on blue LED lights by 10±0.21% and white LED lights 8±0.15% (p<0.05, Kruskal-Wallis). The difference in response to light can be used for glass eel catching applications, especially lamps for eel fish aids and eel conservation to create fishing zones and eels.Keywords: Anguilla bicolor, eel behavior, glass eel, LED light, response to light
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Oreha, Jelena, Aleksandra Morozova, Alberts Garkajs, Muza Kirjušina e Nataļja Škute. "GENETIC DIVERSITY AND POPULATION STRUCTURE OF THE EUROPEAN EEL (ANGUILLA ANGUILLA) IN BALTIC LAKELAND". ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference 1 (13 giugno 2023): 161–65. http://dx.doi.org/10.17770/etr2023vol1.7297.
Testo completoAbstract (sommario):
Anguilla anguilla (Linnaeus, 1758) is the unique catadromous fish species in the Latvian fauna. The Baltic Lakeland area representing naturally recruited and introduced eels. In recent decades, its population has decreased not only in Latvia, but also in Europe. European eel critically endangered due to overfishing of glass eels, blocking of migratory paths, deaths in HPS turbines, water pollution and diseases and parasites. Only some bodies of water are freely accessible to natural migration of eels in Latvia.Currently, its position has been recognized as being critical, and a range of normative acts have been adopted for its restoration, such as the Regulation EC 1100/2007. The restocking programs of the European eel Anguilla anguilla have been conducted for nearly one century in Latvia.This study provides the first data on population structure of freshwater eels in Baltic Lakeland, for use in eel conservation and management of aquaculture on a regional and/or global scale. By analysing the sequences of the Cyt b gene of mtDNA for individuals caught in locations throughout in Baltic Lakeland, we determined the population genetic structure of A. anguilla in the area. The diversity of haplotypes was studied in ten waterbodies from part of Baltic Lakeland, namely Lake Sīvers, Lake Usmas, Lake Ķišezers, Lake Liepājas, Lake Alūksnes, Lake Rāznas, Lake Vialikija Švakšty, Lake Svir, Lake Myadzyel, Myadzelka river. Additionally, this study investigated the affinity of the Latvian populations to other A. anguilla populations around the world.This is the first report about eel’s population genetic diversity in Baltic Lakeland. Haplotype variation was different in all investigated waterbodies. In current studies seven new unique haplotypes were detected. Eel population in Baltic Lakeland shows quite high genetic diversity and rapid population expansions, which possibly is results of intensive restocking program. Sequences characterized Anguilla rostrata in Lake Alūksnes were detected.
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MARCOGLIESE, D. J., e D. K. CONE. "Comparison of richness and diversity of macroparasite communities among eels from Nova Scotia, the United Kingdom and Australia". Parasitology 116, n. 1 (gennaio 1998): 73–83. http://dx.doi.org/10.1017/s0031182097001923.
Testo completoAbstract (sommario):
Species richness and diversity of macroparasite assemblages were compared among American eels (Anguilla rostrata) from Nova Scotia, European eels (A. anguilla) from the United Kingdom (Kennedy, Bush & Aho, 1986; Esch et al. 1988; Kennedy, 1990, 1993), and Australian eels (A. reinhardtii) from Queensland (Kennedy, 1995). Community richness and diversity of the macroparasite fauna of American and European eels did not differ significantly for total parasite component communities, intestinal parasite component communities, and intestinal parasite infracommunities. The similarities in richness and diversity between the parasite communities of American and European eels are not surprising given the common, recent origin of these sister species. However, differences in species composition were noted between Nova Scotia and the UK. Both species of eels were infected by a nearly identical suite of specialists, but differences occurred in the species number and composition of generalist parasites. In addition, generalist species were rarely dominant in Nova Scotia, but commonly so in the UK. These differences can be attributed to the differences in the freshwater fish fauna and their parasites that occur between Nova Scotia and the UK. American and European eels are derived from a common ancestor and, whereas they have carried with them a common suite of specialist parasites during their brief period of independence, they acquired different suites of generalists apparently from their respective continental faunas after they diverged. In contrast, parasite communities of American and European eels were significantly less diverse and speciose than those of Australian eels regardless of scale (total component community, intestinal component community, intestinal infracommunity). These results support the notion that parasite communities have had more time to evolve and/or that tropical conditions have promoted parasite speciation in Australian eels.