Anaerobic energy metabolism of the European eel,Anguilla anguilla L.

Summary Eels, acclimated the 15°C and aerated water (P _{O 2} 130 mm Hg) were exposed to hypoxia (P _{O 2} lowered from 130 to 8 mm Hg in 4 h) and to complete anoxia until loss of equilibrium. Experiments were carried out at night. The mean survival time (LT₅₀) during anoxic conditions proved to be 5.7 h. ATP, ADP, AMP, IMP, CrP, glycogen, lactate, pyruvate, -ketoglutarate, malate, succinate, alanine, aspartate, glutamate and ammonia levels were determined in skeletal muscle and liver of control, hypoxic and anoxic fish. Some of the mentioned parameters were also measured in heart muscle and blood. Hypoxia causes declines of aspartate (muscle), CrP (muscle) and glycogen (liver, heart), and increases of alanine (blood, liver) and lactate (blood, liver, heart). During anoxia, muscle CrP stores are almost completely exhausted and adenylates are partially broken down to IMP. A decrease of glycogen and an accumulation of lactate were observed in all tissues examined. The energy charge of muscle and heart did not drop below 0.79, but in liver tissue it decreased from 0.65 to 0.17. Liver cytoplasm became significantly reduced during anoxia, but such a change of redox state did not occur in muscle. Eels seem to lack the capacity for anaerobic fermentation of glycogen to ethanol, as observed in goldfish. Lactate glycolysis and creatine phosphate breakdown appear to be the main energy producing pathways during anaerobiosis.Abbreviations ALA alanine - ASP aspartate - CrP creatine phosphate - EC (adenylate) energy charge - GLU glutamate - GLC glucose - GLY glycogen - IMP inosine-5-monophosphate - KG ketoglutarate - LAC lactate - MAL malate - PYR pyruvate - SUC succinate - TAN total pool of adenine nucleotides     

Management and restoration of European eel population (Anguilla anguilla): An impossible bargain

The European eel panmicitic population has been declining at least since the 1980s throughout its distribution area. The stocks are now ten times lower than they were initially. The causes of this decline are reviewed in this paper: marine causes such as Gulf Stream shifts are thought to reduce survival of leptocephali larvae during their transoceanic migration, but inland causes are also suspected, i.e. overfishing of all continental stages, obstructions to upstream and downstream migrations, habitat loss, water quality, parasite and xenobiotic contamination, which together contribute to reducing quality and quantity of spawner escapement from European inland waters to sea. Restoration programs have been conducted in several inland hydrosystems in Europe. If local fisheries have been sustained mainly by stocking elvers and glass eels, no significant restoration of the population has been observed suggesting that restoration plans are inefficient, despite significant efforts and relevant technologies (fish passage). The causes for the failure of restoration projects are listed and discussed, and it is shown that the minimum scale to work at is the catchment area. But international cooperation is required to coordinate programs, to determine common objectives and policies. Concepts for sustainable restoration and management are provided and discussed together with the general interest of eel population as a biointegrator of the quality and integrity of inland hydrosystems.     

Changes in enzyme histochemical profiles of identified spinal motoneurons of the European eel,Anguilla anguilla, following cordotomy

Summary The enzyme histochemical profiles of glucose-6-phosphate dehydrogenase (a marker of synthetic performance), succinate dehydrogenase (an indicator of oxidative metabolism), and NADH tetrazolium reductase (a marker of overall neuronal activity) were determined for identified white muscle motoneurons in six control and six cordotomized eels. Images were digitized and mean integrated absorbances obtained using appropriate hardware and software. For motoneurons caudal to the transection site there was a significant decrease in the mean absorbance value for NADH tetrazolium reductases which declines from 0.28 a.u. (arbitrary units) in control animals to 0.23 a.u. in cordotomized animals. However, no significant changes were detected in the activities of glucose-6-phosphate and succinate dehydrogenases. The cross-sectional area of the motoneuronal cell body was not affected by cordotomy. The decrease by around 20% in overall neuronal activity, as expressed by NADH tetrazolium reductase activity, might be expected from the decline in body motility that follows cordotomy. Changes in SDH and G6PDH activities would also be expected to follow this surgery, but none were seen, perhaps because they are compensated for by changes in neuronal metabolism that result from deafferentation.     

Comparative ecology of the European eel, Anguilla anguilla (L., 1758), in a large Iberian river

A total of 1,816 eels were sampled in 1988, from seven sampling areas. Four areas were located in brackish water and the remaining three were located in freshwater reaches of the Tagus river basin. Eels were more abundant in the middle estuary and decreased both in the upstream and in the downstream directions, with a predominance of males in higher density areas. Smaller individuals preferred more peripheral areas, such as margins and upper reaches in the brackish water zone, and the tributaries of the freshwater habitats. It was assumed that this distribution pattern resulted from three main factors: (i) the dominance of larger specimens; (ii) the need to avoid predators and; (iii) the search for better trophic conditions. The condition of the individuals generally decreased toward the upper reaches, apparently due to a corresponding decrease in feeding intensity. The presence of the Belver dam in the main river, 158 km upstream from the sea, seemed to impose major alterations to the described patterns. The concentration of specimens below this impassable obstacle yielded a reduction in the proportion of females and a decrease in the condition and survival of the eels, contributing to a reduction in the spawning success of this population. Suggestions to diminish the effects of the dam, and to preserve the fishery are also presented.     

The effects of calcium and magnesium on water and ionic permeabilities in the sea water adapted eel,Anguilla anguilla L.

Summary The permeability characteristics to water and ions, of the seawater adapted eel, have been studied in the absence and presence of external calcium and magnesium.The absence of these divalent ions from the external medium produces an increase in the unidirectional and net water fluxes as well as a decrease in temperature coefficients. Similarly, an increase in the effluxes of sodium and chloride and a large increase in the passive loss of these ions was observed when fish were transferred to deionized water. The stimulating effect of externally added (10 mM) potassium on the sodium and chloride effluxes, when fish are transferred to fresh water is abolished in the absence of calcium and magnesium (Fig. 1). These kinetic changes are accompanied by ultrastructural changes concerned principally with the chloride cells (Figs. 2 and 3).The results are discussed in terms of the possible role of calcium and magnesium in the maintenance of the hydro-mineral equilibrium of the eel.     

Gluconeogenesis in isolated liver cells of the eel,Anguilla japonica

Summary The pathway of gluconeogenesis from pyruvate, lactate and alanine was investigated in isolated liver cells of the eel. Amino-oxyacetate, a transaminase inhibitor, inhibited gluconeogenesis not only from lactate, but also from pyruvate by 60%.d-Malate did not inhibit gluconeogenesis from either of the substrates (Table 1 A).The effects of various amino acids on gluconeogenesis were investigated. Leucine accelerated gluconeogenesis from pyruvate or alanine (Table 2). Leucine promoted the incorporation of¹⁴C-pyruvate into glutamate and aspartate, and increased the glutamate content. The specific activity of¹⁴C-aspartate was increased markedly by leucine (Table 5).From the investigation of subcellular distribution of enzymes unique to gluconeogenesis, it was found that pyruvate carboxylase was located almost exclusively in the mitochondrial fraction, and that phophoenolpyruvate carboxykinase and aspartate transaminase were located in both the mitochondrial and the cytosolic fractions (Table 7).From these results it is concluded that the oxaloacetate-aspartate pathway is a major route in gluconeogenesis from any of the substrates in the eel liver.Abbreviations AOA amino-oxyacetate - PEP phosphoenolpyruvate     

11-Ketotestosterone induces silvering-related changes in immature female short-finned eels, Anguilla australis

The developmental transition from a residential, immature ‘yellow’ eel to a migratory, maturing adult ‘silver’ eel is accompanied by many morphological changes that appear to be under endocrine control. High circulating levels of the teleost, and usually male-specific, androgen 11-ketotestosterone (11-KT) are found in migrating female short-finned eels, Anguilla australis. We examined the role of this steroid in silvering by implanting immature, female short-finned eels either with blank vehicles or with vehicles containing 11-KT. Six weeks after they had received the implants, eels treated with 11-KT had developed ‘chisel-shaped’ snouts and black pectoral fins with tapered ends, and the size of their eyes had increased significantly. 11-KT treated eels had a thicker dermis than control eels and an epidermis with fewer or no mucous cells. Ventricular mass at the end of the experiment was two-fold larger than in control eels. 11-KT treated eels also had larger livers and gonads. Ovaries contained predominantly cortical alveolus stage III oocytes, as opposed to the smaller gonads of control eels containing previtellogenic stage II oocytes. All of these changes correspond to changes during the developmental transition from yellow to silver eels in the wild. This demonstrates that silvering in eels is under endocrine control and that the presumed male-specific steroid 11-KT is capable of inducing silvering-related changes in a female teleost. We discuss how species-specific responses to 11-KT may differ depending on tissue-specific androgen receptor abundance and how a dual demand on liver function can explain the apparently positive effects of 11-KT on liver growth.     

Advancing provision of multi-species fish passage: Behaviour of adult European eel (Anguilla anguilla) and brown trout (Salmo trutta) in response to accelerating flow

The behavioural response of downstream moving European eel (Anguilla anguilla) and brown trout (Salmo trutta) to velocity gradients created by orifice weirs placed in a flume were studied. The aim was to identify interspecific variation and test two hypotheses: (1) a more abrupt velocity gradient would induce a higher avoidance response and over a greater distance, and (2) fish would acclimate to the velocity gradient by incrementally sampling conditions closer to the orifice until successful passage occurred. European eel moved along the channel floor and walls, responding after physical contact with the weir. Brown trout moved downstream head first and switched orientation at the velocity gradient without contacting the structure. Brown trout spent longer than European eel immediately upstream of a channel floor orifice, although time to pass was similar; but less time at a mid-column orifice despite taking longer to pass. The mid-column orifice delayed both species longer. European eel passed orifices head first on initial encounter with no rejections, whereas brown trout passed tail first. Positions where brown trout first switched orientation and closest point to the orifice reached during initial approach occurred closer to a channel floor than mid-column treatment. Brown trout did not appear to acclimate to the velocity gradient by sampling successively closer to the orifice. Interspecific variation in behaviour remains a key challenge in developing multi-species fish passes.     

Starvation and the metabolism of hepatocytes isolated from the American eel,Anguilla rostrata LeSeur

Summary Gluconeogenic, lipogenic, glycogenic and oxidative rates were estimated from¹⁴C-lactate,¹⁴C-alanine and¹⁴C-aspartate using a hepatocyte preparation isolated from starved immature American eels,Anguilla rostrata. Lactate gluconeogenesis increased significantly during starvation at 5 and 15°C. Alanine gluconeogenesis generally decreased during starvation. At the 2nd month of the starvation at 5 and 15°C, and the 8th month of starvation at 15°C, however, alanine gluconeogenesis was significantly higher than in the fed control. These increases in alanine gluconeogenesis occurred during a period of high glucose demand. Aspartate gluconeogenesis was quantitatively minor when compared to the other two substrates. Glycerol synthesis and esterification from the three substrates increased until the 5th month at 5 and 15°C followed by a gradual decline thereafter. Significant increases in glycogen synthesis occurred between the 3rd and the 5th months at 15°C, but rates were small compared to glucose synthesis. Rates of substrate oxidation appeared sufficient to provide adequate ATP to sustain gluconeogenesis in both the fed and starved eel hepatocyte. Glucagon stimulated lactate gluconeogenesis, but not amino acid gluconeogenesis in late starved eel hepatyocytes. Major changes in metabolite concentrations that occurred during starvation were increases in plasma glucose and amino acids; a significant liver glycogen depletion at the 2nd month followed by a return to control values at the third month; and, a significant protein depletion in white skeletal muscle at the 3rd month. These data suggest that lactate glucogeogenesis, but not amino acid gluconeogenesis or glycogenolysis, is the major source of tissue carbohydrates during eel starvation.This work was supported from operating grants to TWM from the National Research Council of Canada (A6944)     

Individual patterns of rhythmic swimming activity in Anguilla anguilla glass eels synchronised to water current reversal

The existence of distinct patterns of activity and swimming behaviour were tested in individual European glass eels by means of Bayesian inference mixture modelling. 36 glass eels were tagged using Visible Implant Elastomer and added to 36 untagged glass eels in February and April. Each group was presented with a change in water current direction every 6,2 h and videotaped during 2 weeks. Two hypotheses were tested: (i) all individuals display a similar pattern of behaviour within a tidal period, glass eels showing both positive and negative rheotaxis in opposite phase (M1 model) and (ii) individuals are distributed in two different groups, some glass eels swimming with and the others against the current (M2 model). Results showed that most glass eels displayed a positive or a negative rheotaxis and only a small number exhibited both behaviours. All swimming behaviours were synchronised to a change in current direction with a period close to the tidal one. Results are discussed in relation to synchronisation and migration behaviour.     

Characterization of gluconeogenesis in hepatocytes isolated from the American eel,Anguilla rostrata LeSueur,

Summary Isolated hepatocyte preparations from fed immature American eels,Anguilla rostrata Le Sueur, were used to study gluconeogenic, lipogenic, glycogenic and oxidative rates of radioactively labelled lactate, glycerol, alanine and aspartate. Eel hepatocytes maintain membrane integrity and energy charge during a 2 h incubation period and are considered a viable preparation for studying fish liver metabolism.Incubating eel hepatocytes with 10 mM substrates, the following results were obtained: glycerol, alanine and lactate, in that order, were effective gluconeogenic substrates; these three substrates reduced glucose release from glycogen stores, while aspartate had no such effect; lactate, alanine and aspartate led to high rates of glycerol production, with subsequent incorporation into lipid; incorporation into glycogen was low from all substrates; and, alanine oxidation was seven times higher than that observed with other substrates.When eel hepatocytes were incubated with low or physiological substrate concentrations gluconeogenic rates from lactate were twice those from alanine; rates from aspartate were very low. Glucagon stimulated lactate gluconeogenesis, but not amino acid gluconeogenesis, and had no significant effect on glycogenolysis. Cortisol increased gluconeogenic rates from 1 mM lactate.Thus, in the presence of adequate substrate, eel liver gluconeogenesis is preferentially stimulated relative to glycogenolysis to produce plasma glucose. These data support three important roles for gluconeogenesis: the recycling of muscle lactate, the synthesis of glucose from dietary amino acids to supplement glucose levels, and the production of glycerol for lipogenesis.This work was supported from operating grants to TWM from the National Research Council of Canada (A6944)     

Effects of body condition and water temperature on Anguilla anguilla glass eel migratory behavior

Glass eels arriving from the sea use alternative migratory tactics, leading either to the colonization of rivers or to an early settlement in marine or estuarine habitats. In the field, the migration may be environmentally affected by water temperature and the migratory behavior could be physiologically dependent on the body condition (energetic status). To investigate how these environmental and physiological effects on the migration are behaviorally mediated, we experimentally tested the effects of changes in water temperature and body condition on locomotor activity (upstream swimming) and salinity preference of Anguilla anguilla glass eels. Low water temperature reduced significantly both locomotor activity and preference for freshwater, in accordance with field data showing that low water temperatures hinder both the estuarine migration and river recruitment. Glass eels switched from a freshwater- towards a saltwater-preference as their body condition decreased, confirming that the energetic status may affect the migratory behavior. We suggest that, in the wild, this condition-dependent change in salinity preference of low body condition glass eels induces an early settlement in marine or estuarine habitats. Such a behavioral shift, stopping the energy expenditure linked to river-oriented migratory behavior, may be adaptive by limiting the probability of death due to exhaustion. Our results show that the glass eel migratory behavior, through locomotor activity and salinity preference, may be controlled by interacting physiological and environmental factors.     

种间竞争对香蒲与芦苇生长的影响

为了探究种间竞争对香蒲（Typha domingensis）与芦苇（Phragmites australis）生长的影响,利用根系分隔盆栽试验研究了3种不同分隔方式条件下香蒲与芦苇的种间竞争特性,包括塑料膜分隔（根系完全分隔,无相互作用,无物质交换）、尼龙网分隔（根系部分分隔,无相互作用,有物质交换）和不分隔（根系完全相互作用,有物质交换）,分析了香蒲与芦苇根系形态和地上部生长的变化,探究香蒲与芦苇种间竞争的差异。结果发现（1）在尼龙网分隔和不分隔处理中芦苇具有明显的劣势。与塑料膜分隔处理相比,芦苇的总生物量、植株密度在尼龙网分隔和不分隔处理中分别减少了39.14%、49.41%和82.08%、79.22%,总根长、总根表面积、总根体积分别减少了40.53%、44.84%、62.52%和85.7%、82.45%、89.67%,且均具有极显著差异（P<0.01）;根系分隔方式也影响芦苇的株高、茎粗和叶片数,表现为不分隔 > 塑料膜分隔 > 尼龙网分隔。（2）与塑料膜分隔处理相比,香蒲总生物量在尼龙网分隔和不分隔中虽有增加,但差异不显著,植株密度和株高在尼龙网分隔和不分隔处理中都有增加且具有显著差异（P<0.05）,其总根长、总根表面积、总根体积在尼龙网分隔中分别增加了57.93%、26.5%、8.04%,但在不分隔处理中分别减少了11.57%、14.92%、11.39%（P<0.05）,虽然根系的相互作用对香蒲根系的生长具有促进作用,但植物种间根系相互作用越强,对两者的生长越不利。（3）在不同的分隔方式中,芦苇与香蒲间也存在明显变化。在不分隔处理中,香蒲的生物量和植株密度是芦苇的1.7倍和6.74倍,与塑料膜分隔处理相比增加了6倍,表明芦苇与香蒲根系的完全相互作用,显著削减了芦苇的繁殖生长,增加了香蒲的根系分蘖。（4）通过种间相互作用强度（RII值）分析也表明,尼龙网分隔和不分隔处理下芦苇表现为抑制作用（RII值为负值）,香蒲表现为促进作用（RII值为正值）。香蒲与芦苇互作对芦苇具有抑制作用,说明种间相互作用是能改变植物的适应性和植物群落的繁殖,同时也表明植物根系不仅在吸收土壤中的水和养分中起着关键作用,在种间关系中也起着重要作用。因此利用种间竞争控制植物生长,可以为保护生物多样性和生态系统的功能提供有效的技术支撑。     

High density lipoprotein binding protein of eel (Anguilla japonica) liver with specificity of binding to apoAI as a ligand

High-density lipoprotein (HDL) binding protein (HBP) was isolated from the microsomal fraction of eel liver homogenate by affinity chromatography with a HDL-column. After SDS-PAGE and blotting, HBP on the PVDF membrane was detected by FITC-labeled HDL and apolipoprotein AI (apoAI) as a ligand. HBP in the microsomal fraction was most abundant among microsomal, mitochondrial and cytosolic fractions. The HBP isolated by a HDL-column consisted of at least three proteins with low molecular weights of 18.5, 14.5 and 13.5 kDa; the main component was 14.5 kDa. These proteins are not products of protease digestion, as the procedure was carried out in the presence of protease inhibitors including (p-aminophenyl) methansulfonyl fluoride, 4-(2-aminoethyl)-benzenesulfonyl fluoride, pepstatin A, E-64, bestatin, leupeptin, aprotinin and EDTA. The HBP specifically bound to FITC-apoAI and faintly bound or did not bind to FITC-apoAII. Furthermore, binding of HDL labeled with lipophilic fluorescence to isolated eel hepatocytes was inhibited by the antibody to apoAI, but not inhibited by the antibody to apolipoprotein AII (apoAII). These results strongly suggest that the HBP isolated from the microsomal fraction is present on the plasma membrane of eel liver and plays important roles for the lipid transport through the interaction with HDL.     

Domoic acid production by Pseudo-nitzschia australis and Pseudo-nitzschia calliantha isolated from North Chile

The morphology and toxicity of the four ubiquitous species belonging to the genus Pseudo-nitzschia found in mixed blooms of phytoplankton from northern Chilean waters were studied. The phytoplankton samples and cultures obtained were identified by scanning electron microscopy, revealing the presence of Pseudo-nitzschia australis, P. calliantha, P. pseudodelicatissima and P. subfraudulenta. This is the first report of P. calliantha in northern Chile. Toxin analyses using the LC–MS method confirmed the presence of domoic acid in P. australis and P. calliantha. Domoic acid was not detected in cultures of P. subfraudulenta. This study therefore confirms P. australis and P. calliantha as an unequivocal source of domoic acid in Chilean waters. P. australis is probably the most important producer of amnesic shellfish toxin in view of its domoic acid content. However, more research is needed to evaluate the potential for toxin production in P. pseudodelicatissima.     

Recruitment abundance estimation: Role of glass eel (Anguilla anguilla L.) response to light

Most fish populations are declining worldwide and their management would benefit from a better estimation of recruitment. In glass eels, field studies suggest that estuarine migratory glass eels are sensitive enough to light to change their vertical location according to factors such as water turbidity and/or moon brightness. The response of glass eel (Anguilla anguilla L.) to light was tested in the laboratory using boxes where fish could choose between a lit and an unlit side. Responses were quantified as the proportion of glass eels remaining in the unlit chamber. Decreasing light levels were used and tested on different “age” glass eels (“age” in days since capture). In addition, measures of light at different depths of the water column were carried out in the Adour estuary (43°30′ N, 1°30′ W). The glass eel light avoidance level was lower in non-pigmented glass eel (less than 10 ^− 10 W cm ^− 2), than in pigmented ones (10 ⁻⁹-10 ^− 8 W cm ^− 2). These results and field data on the measurement of light energy in the water column of Adour estuary are compared with previously published data on the estuarine migration of glass eel.