欧洲鳗血清免疫球蛋白纯化及部分特性分析

采用饱和硫酸铵分步盐析法结合柱层析提取，纯化欧洲鳗血清免疫球蛋白（Ｉg) ,实验证实欧洲鳗Ｉg主要分布在硫酸铵饱和度３０％－５０％的区间内，Ｓephacry1-S200进一步提纯的Ｉg主要存在于第一个蛋白峰，而Ｓepharose-4B柱层析提纯的Ｉg则存在于第二个蛋白峰，ＤＥＡE-52脑子交换柱层析可进一步纯化Ｓepharose-4B柱层析的产物，ＥＬＩＳＡ和Western-blot分别证实上述提取物具有抗体的免疫学活性，ＳＤＳ－ＰＡＥＧ分析纯化的Ｉg，显示了洲鳗Ｉg重链约为６８kD，轻链约为２６kD.     

欧洲鳗免疫球蛋白单克隆抗体的制备与特性

应用杂交瘤单克隆抗体技术制备了13个分泌抗欧洲鳗免疫球蛋白的单克隆抗体细胞株，并对这些单克隆抗体的特性进行了分析。经抗体级份和亚级份测定，其中IgM有3株，IgG1有5株，IgG2a有3株，IgG2b有2株；所有的单克隆抗体与欧鳗免疫球蛋白均有ELISA反应特性，抗体滴度10^4-10^7，有七株单抗具有WESTERN BLOT反应特性，能在变性条件下识别欧鳗免疫球蛋白的重链。进一步实验证实这些单抗能特异地识别欧洲鳗、日本鳗的免疫球蛋白，而与鲫、淡水白鲳、罗非鱼、胡子鲶、美洲斑点叉尾Hui血清免疫球蛋白以及水产动物常见病原菌如气单胞菌、爱德华氏菌、弧菌、柱状屈桡杆菌、沙门氏菌及大肠杆菌等无任何交叉反应。单克隆抗体9D7，对纯化的欧洲鳗免疫球蛋白的检测灵敏度为16ng。实验结果证明这些单抗具有高度特异、高度灵敏等特点，可用于鳗鲡免疫球蛋白的结构分析、免疫应答水平监测和病原诊断，具有广阔的应用前景。     

Variations in the population dynamics of the European eel Anguilla anguilla (L.) along the course of a Cantabrian river

Abstract– The size, density and production rate of eel were determined at 16 contrasting sites of 4 streams along the course of a Cantabrian river over the years 1990–1993. In addition, the diel cycles of feeding activity were determined monthly in another tributary over the year 1991–1992. Eels in the Esva were small, short-lived and mostly males (>99%). The seasonal patterns of eel density, feeding activity and condition were tightly fitted with each other, size-independent and regulated mainly by water temperature. Mean eel size increased with distance from the river mouth, but at each site, it remained similar between seasons and years. In contrast, density decreased upstream and showed marked seasonal and annual fluctuations. For all the sites, the number of eels increased in spring and summer and peaked by late autumn, coincident with higher water temperature and lower discharge. Mortality and migration rates were correlated with eel numbers for each stream, suggesting a densitydependent regulation. Production rates were correlated with distance from the river mouth, which explained only 10.2% of the variation, but they were also correlated with the initial and mean numbers, suggesting that site-specific factors acting upon density also influence production. Average production for the first year was 158.6 kg^–ha^–1. year^–1 (range 56.5–378.0) but decreased to 104.2 and 89.7 in the next 2 years. The reduction in the numbers of eels rather than the later reduction in mean size was responsible for this decrease. Monthly water temperature, distance from the river mouth and the initial number and size of eels for each site explain most of the variation observed in the population parameters along the course of the Esva River.     

Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Abstract –  Modelling-governing patterns of European eel ( Anguilla anguilla L.) distribution of four eel size classes (<150, 150–300, 300–450 and >450 mm) in the Frémur basin (northwest France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro- and microscale factors, such as distance from the sea, depth and flow velocity, have the most significant influence on the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to the distance from the sea showed that densities increase weakly upstream. Another outcome was the variations in habitat preference according to the eel size, even if this species is spread over practically every type of microhabitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesise that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm.     

Developmental changes in pituitary–thyroid axis, and formation of gonads in leptocephali and glass eels of Anguilla spp.

SUMMARY: Pituitary, thyroid gland and gonads in leptocephali of Japanese eel Anguilla japonica (19.8–32.6 mm in total length), A. obscura (45.0 mm), and A. bicolor pacifica (49.5 mm) and those in glass eels of the Japanese eel were histologically and immunohistochemically examined in order to observe the developmental changes of these endocrine organs in the Anguillidae. The pituitary, consisting of adenohypophysis and neurohypophysis in Japanese eel leptocephali over 22.5 mm, did not contain thyroid stimulating hormone (TSH) immunoreactive cells. Such cells were, however, detectable in the more developed pituitaries of leptocephali of A. obscura and A. bicolor pacifica and in those of glass eels. Conversely, thyroxine (T₄)-immunoreactive thyroid follicles could be detected in all specimens, both leptocephalic and glass eel. Only in glass eels, gonads were found in the body cavity, and these gonads harbored one or two primordial germ cells (PGC) per cross-section. Our results indicate that thyroid hormones (TH) production started prior to TSH production, and that TSH and TH are both secreted during the metamorphosis from leptocephalus to glass eel. Therefore, it is plausible that the TSH–TH axis is involved in the metamorphosis from leptocephalus to glass eel, but not in the early growth from preleptocephalus to leptocephalus.     

Spatiotemporal variation in the distribution of eel (Anguilla spp.) populations in three New Zealand lowland streams

Abstract – Populations of shortfinned eel ( Anguilla australis ) and longfinned eel ( A. dieffenbachii ) were sampled at randomly chosen sites along the length of three New Zealand streams during summer for three consecutive years to determine their variability in size distribution between streams, reaches (within streams) and years. The longfinned eel was numerically dominant in two of the streams, whereas the shortfinned eel was more abundant in the third stream. For comparisons, the data were stratified into 100-mm size classes for eels ≤600 mm long, whereas eels >600 mm were pooled into a single class. Log-linear analysis indicated that the size distribution of both species differed significantly between streams. Moreover, the size distribution of shortfinned, but not longfinned eels, differed significantly between reaches. Neither species showed significant change in size distribution between years. In contrast to the shortfinned eel, the density of longfinned eel ≤100 mm long was consistently low for all three years, which probably indicates poor recruitment.     

Differences in head shape of the European eel, Anguilla anguilla (L.)

Differences in eel, Anguilla anguilla (L.), head shape were the result of greater increases in head width, rather than changes in head length. The ratio of head width:total length (HW:TL) increased significantly ( t -test, P < 0.05) from the glass-yellow eel stage. Cultured yellow eels were exclusively narrow headed (mean HW:TL = 0.027, range = 0.023–0.032), while wild yellow eels displayed an array of head shapes (mean HW:TL = 0.033, range = 0.023–0.046). Therefore, broad heads (HW:TL 0.033) occurred only among wild yellow eels sampled and may have resulted from diet. Cultured yellow eels consumed only small pellet material. Of wild yellow eels stomachs containing food, 78% of broad-headed eels consumed large and/or hard-bodied organisms (e.g. beetles, fish, molluscs and Notonecta sp.), while 83% of narrow-headed eels consumed exclusively small/soft-bodied prey (e.g. amphipods and chironomids).     

Decreasing eel stocks: survival of the fattest?

Abstract –  Since the 1980s, the European eel Anguilla anguilla stock is in steep decline. Lipid reserves are essential to cover energetic requirements for silver eel migration and reproduction. Two large and independent data sets from Belgium and The Netherlands show an average one-third decrease in fat contents of yellow eels over the past 15 years. Also Le Cren's relative condition factor decreased. On the basis of the somatic energy reserves, reproductive potential of eels from various latitudes over Europe was estimated, assuming fat levels in yellow eel are indicative of those in silver eels. Only large individuals, females as well as males, with high lipid content seem to be able to contribute to the spawning stock. The decrease in fat content in yellow eels may be a key element in the stock decline and raises serious concerns about the chances of the stock to recover.     

The use of fyke nets as a quantitative capture technique for freshwater eels (Anguilla spp.) in rivers

Abstract  Fyke netting is a convenient and effective technique for capturing freshwater eels, and catch-per-unit-effort is usually assumed to be an index of eel abundance. The present study investigated the potential of depletion fishing using baited fyke nets to obtain population estimates of longfin eels Anguilla dieffenbachii Gray, in a river in the South Island of New Zealand. The probability of capture (capture efficiency) of a single night's fishing increased with increasing size of eel, and ranged from 0.2 to 0.9 for eels <400 mm, to 0.7–0.9 for eels ≥500 mm. The capture efficiency of baited vs unbaited nets was assessed in a small stream that was electric fished after netting trials were completed. Baited nets proved to be an effective method of assessing abundance of longfin eels (>400 mm) but not shortfins ( A. australis Richardson); capture efficiency of the population of longfins (the sum of fyke caught and electric fished eels) was 0.4 for a single night's fyke netting, increasing to 0.8 over four nights. Comparable efficiencies for shortfins were <0.1 and 0.3 respectively. Unbaited nets were markedly less efficient for both species.     

Patterns of silver eel (Anguilla anguilla L.) sex ratio in a catchment

Abstract –  Changes in the numbers and size-class structure of European silver eels, Anguilla anguilla , in the River Frémur (France) were examined over a 9-year period after installation of downstream eel passes. The number of silver eels migrating downstream peaked in 1999, then decreased strongly and steadily after 2000, reaching relatively low levels. At the same time, a gradual shift in the silver eel sex ratio from a dominance of males (size from 270 to 442 mm, age from 3 to 6 years) to females (size from 366 to 1112 mm, age from 4 to 9 years) was recorded. Possible explanations for the escapement patterns observed are environmental sex determination and the installation of eel passes on the main hydraulic engineering structures in 1992 and 1996.     

Variability in growth rates of freshwater eels (Anguilla spp.) in New Zealand

Abstract— Both species of New Zealand freshwater eels (the shortfinned eel Anguilla australis and the longfinned eel A. dieffenbachii ) are widespread and abundant, supporting important commercial and recreational fisheries. This article reviews growth studies from 35 widely distributed sites throughout New Zealand and discusses factors that influence growth rates. Length at given age is characterized by high intra- and inter-population variability; growth rates for eels >30 cm are typically slow (2–3 cm per year) and linear, with females generally growing faster than males. Water temperature affects the length of the growing season, although growth rates are not correlated with latitude. Other factors suggested as affecting growth rates are eel density, quantity and quality of food, and interactions between both eel species. Al though growth of some New Zealand eel populations is the slowest recorded for any species of Anguilla , growth in culture can be rapid, similar to that of other temperate eel species.     

Population structure of the Japanese eel Anguilla japonica as examined by mitochondrial DNA sequencing

SUMMARY: To examine the population structure of the Japanese eel Anguilla japonica , mitochondrial DNA sequence analysis was made for various samples of glass eels that might reflect genetic characteristics of spawning aggregates. The mitochondrial DNA from a total of 51 glass eels collected at Tanegashima Island, Kanagawa and Ibaraki in different periods within an inshore migrating season was sequenced for a 615 base-pair fragment from the tRNA^Thr gene to the central part of the control region. The DNA region was so variable that no individual was found to possess the same sequence, although average sequence differences within samples (1.07–1.63) were not large. Average sequence differences between samples (1.22–1.57) were comparable to those within samples, suggesting no genetic heterogeneity among samples. Tree analysis of the sequences showed neither a geographical nor temporal structure of population. Furthermore, although all DNA sequences from the present study were different from one another, two sequences were found to be the same with those reported from individuals collected in different localities in different years. Altogether, the present mitochondrial DNA sequence analysis of glass eels did not provide any evidence for genetic subdivision of the Japanese eel population.     

Size-related differences in diel activity of two species of juvenile eel (Anguilla) in a laboratory stream

Abstract – The diel activity of three size groups (small=<100 mm; medium=100–199 mm; large=200–299 mm total length) of juvenile shortfinned ("shortfin") eels ( Anguilla australis ) and longfinned ("longfin") eels ( A. dieffenbachii ) was tested in a laboratory flow tank over a 48-h period during summer. All size groups of both species were nocturnally active, with the eels hiding in the substratum during the day and coming out on top of the cobbles from dusk to dawn, to feed. During the foraging period, the numbers and activity of all sizes of longfins visible were greater than those seen of shortfins, with the differences being more pronounced for small and medium eels. The activity of all eels consisted mostly of foraging by crawling, searching and probing for prey among the cobbles. Rate of activity increased with size of eel for both species. Small eels of either species did more swimming than eels of the larger sizes, whereas large eels were observed more frequently with only their head out of the substrate than were the smaller individuals. Feeding of small eels within the interstitial spaces of the streambed may explain their significantly lower activity on top of the substrate at night. The significantly lower rate of activity recorded for shortfins than longfins of all sizes may be due partly to their ability to feed within the interstices of the stream bed, and (or) longer time to recover from handling and habituate to the test environment. ^Note     

花鲈免疫球蛋白的分离纯化及部分特性分析

分离纯化了花鲈(Lateolabrax japonicus)血清免疫球蛋白(Ig),并对其特性进行初步研究与分析.采用山羊-IgG(Goat-IgG)免疫花鲈并制备血清,分别采用硫酸铵分级沉淀法、A蛋白亲和层析法及Goat-IgG偶联亲和层析法提取花鲈Ig,对提取组份进行了蛋白浓度测定、间接ELISA效价测定、SDS-PAGE和Western-blotting分析.结果表明,采用硫酸铵分级沉淀法提取的花鲈Ig主要集中在硫酸铵饱和度为30%～50%的区间,其中45%饱和度硫酸铵富集的的抗体比活最高,ELISA效价为2×104/mg蛋白,比血清ELISA效价提高2.2倍;A蛋白柱亲和层析可得单一蛋白峰,洗脱峰集中在洗脱体积0.8～1.6 mL,处,占洗脱蛋白总量的76.2%,峰值的ELISA效价为1.37×105/mg蛋白,抗体得率为2.57%;Goat-IgG偶联Sephrose 4B亲和柱层析也可得单一蛋白峰,洗脱峰集中在洗脱体积1.4～2.8 mL处,占洗脱蛋白总量的72.4%,峰值的ELISA效价为1.39×105/mg蛋白,抗体得率为2.63%.以上3种提取方法均可得到79 kD的重链和29 kD轻链,表明可得到纯化的免疫球蛋白;采用鼠抗花鲈Ig血清和单抗AA5经Western-blotting证实提取成份为花鲈Ig.本研究表明,A蛋白柱和Goat-IgG偶联柱亲和层析均可用于花鲈Ig的提取,其中A蛋白柱法获得的洗脱峰值更为集中,抗体效价高,且提取过程不需要Goat-IgG免疫鱼体,是一种更为有效的免疫球蛋白提取方法.     

Errors in ocular index measurements in European eel Anguilla anguilla (L.)

Abstract –  Knowledge of maturation state of eels ( Anguilla anguilla , L.) based on ocular index (OI) serves management and research functions, such as estimating how much silver eel actually could escape from a particular basin or determining more precisely the developmental biology of a particular eels. OI implies the measurements of five variables (total length and eyes diameters) in a formula which can be sensitive to measurement error. To investigate this issue, we carried out a comparative study using 13 European eels harvested in Camargue (Rhône Delta, France) and three replicated measurements by three different observers. The estimated amplitude of OI imprecision at a 95% confidence level was 1.8 whatever eel and observer. Such error may lead to classification problems particularly when OI values are close to the threshold values used to discriminate between yellow and silver stages. This study not only raised the problem of the OI imprecision but also brought up the need to develop standardised protocol for identifying silver eels. To reach this goal, two different ways are proposed in conclusion.     

Analysis of distribution patterns of yellow European eels in the Loire catchment using logistic models based on presence–absence of different size-classes

Abstract –  We used logistic models to analyse the longitudinal distribution patterns of yellow European eels in the Loire catchment (France). Our models for predicting the presence of yellow eels supported contrasting spatial patterns according to the size of individuals and catchments. The smallest eels (mainly <150 mm and secondly 150–300 mm) were confined to downstream areas, but rapidly colonised upstream reaches. By contrast, larger eels were distributed further inland but tended to become more sedentary. In addition, a higher density of barriers to migration in the Maine catchment (a large catchment within the Loire catchment) probably delayed the upstream colonisation compared with the rest of the Loire catchment. These results suggest that logistic models may be a useful and efficient tool: (1) for the assessment of eel status and trends in freshwater systems; and (2) for the assessment of the consequences of local perturbations or conversely improvement of colonisation.     

Effect of aromatable androgen (17‐methyltestosterone) on induced maturation of silver European eels (Anguilla Anguilla): Oocyte performance and synchronization

The reproductive performances of silver European eel in term of gonad development and egg production, employing slow‐release implants with the androgen 17‐MT (1 mg) in combination with traditional weekly injection of carp pituitary extract (CPE) was evaluated. Wild female European eels (Anguilla anguilla) underwent a standard induction protocol with CPE and were randomly divided into three groups (N‐group, no implant; Y‐group, with implant; and control, C‐group, no treatment). The results showed that 17‐MT‐treated females (Y‐group) reproduced spontaneously about 6 weeks earlier than the N‐group females with a saving of almost 40% in CPE and time of induction. Concerning artificial induction of maturation in female silver eels, our study demonstrated that they positively respond to androgen exposure also in terms of eggs productivity. Indeed, Y‐group was more productive than N‐group: in Y‐group, 11 eels ensured an eggs production that exceeded 50% of initial body weight (BW), whereas in N‐group only three eels have exceeded this value. The results suggest that 17‐MT should be considered in future protocols for the improvement of the artificial reproduction of female silver European eels.     

Assessing the impact of hydropower and fisheries on downstream migrating silver eel, Anguilla anguilla, by telemetry in the River Meuse

Abstract –  European eel Anguilla anguilla is in strong decline. We assessed the relative impact of fisheries and hydropower during the downstream migration of silver eel in the River Meuse in the Netherlands using radio-telemetry. For this, 16 fixed detection stations (Nedap Trail-System^®) were used, each covering the entire river width, including all outlets to sea, and two covering the entrances of the two hydropower stations present. In September 2002, 150 silver eels were surgically implanted with Nedap-transponders and released at the catch site. Of these, 121 started to migrate downstream of which 37% successfully reached the North Sea. Hydropower mortality was at least 9% and assessed to be 16–26%. Fisheries mortality was at least 16% (reported recaptures) and estimated to be 22–26%. A clear difference was found in passage behaviour at hydropower stations, where 40% showed recurrence, in contrast to the river stations where this hardly occurred, indicating a hesitation to pass the turbines. Also a difference was found in diurnal pattern; 63% of the eels that passed through the turbines did so during the first 5 h of the night, whereas for the stations on free-flowing sections this was only 35%.     

Anosmic Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> can no longer detect magnetic fields

ABSTRACT:   Magnetosensitivity in anosmic Japanese eel Anguilla japonica was examined by conditioning and electrocardiography. Five eels from a freshwater farm in Kagoshima, Japan, were made anosmic by injection of boiling petroleum jelly (130–140°C) into the nasal cavity, a technique widely used in studies on olfaction and olfaction-related behavior of eels. Another five eels were not injected with boiling petroleum jelly and served as controls. Conditioning consisted of exposure of eels to an imposed magnetic field of 192 473 nT. After complete conditioning of the eels, the imposed magnetic field was reduced from 192 473 nT to 12 663 nT during the tests. The control eels showed a significant conditioned response (i.e. slowing of the heart beat) to the magnetic field after one set of conditioning runs. The anosmic eels did not respond to the magnetic field, presumably due to damage of the olfactory organ from the jelly injection. The results suggest that Japanese eels have a magnetosensitive organ in or around the nares. At 1 month after the anosmia treatment, there was no visible trauma to the olfactory lamellae of anosmic eels.     

Dynamics of upstream migration of the European eel, Anguilla anguilla (L.), in the Rivers Severn and Avon, England, with special reference to the effects of man-made barriers

The upstream migration of European eels, Anguilla anguilla (L.), was studied during 1991–1993 in the Rivers Severn and Avon using traps mounted on weir or sluice barriers. Only pigmented elvers and juvenile eels were trapped at the tidal limits, catches being equivalent to about 0.8% of the commercial glass eel catch in the lower estuary. First catches were made as temperatures rose above 10–11 °C. Pigmentation-stage analyses and body size data indicated that estuarine migration was slow and that natural mortality was probably very high. Relatively more eels were trapped in the Severn compared with the Avon, but in both rivers the number of immigrants decreased rapidly upstream of the tidal limits, whilst the average size and age increased. The number and severity of weir and sluice barriers to be surmounted exerted a greater effect than distance alone. Recapture rates of marked eels were low (1–2%), implying variable migratory tendencies and/or high mortality. Mean migration rate in the non-tidal rivers was 0.64 ± 0.6 km day^–1 and some eels were not recaptured until one or two years after release. Speed of migration increased with temperatures above 15–16 °C. Relationships between migration dynamics, barriers and the scarcity of upriver stocks of eels and distorted population structures in the two rivers are discussed. Recommendations are made for the provision of passes and/or stocking to enhance migration and recruitment.