Review. Levels of Recirculating Reproductively-related Steroid Hormones in Female Elasmobranchs. Implications for Reproduction in a Captive Environment

Chondrichthyans are a diverse group in terms of reproductive mode, which range from extended oviparity to placental viviparity. Although the reproductive biology of several species has been investigated, the reproductive physiology of only a few species has been reported. Only recently have the physiological factors of reproduction in cartilaginous fishes received attention. The information gained on reproductive cycles (both gonadal and uterine) has shown some similarities as well as differences between species. The serum levels of androgens, oestrogens, and progestins have been examined in several elasmobranch species and it has been shown that they are important in regulating key events in reproduction. The endocrine control of reproduction in elasmobranchs is more similar in many ways to higher vertebrates such as mammals than to teleosts. In general, the role of progesterone becomes more important than that of oestrogen in the transition from oviparity to viviparity. In addition, the roles of peptide hormones such as relaxin and the neurohypophysial hormones become increasingly important in viviparous species as in higher vertebrates. It is vital to understand the environmental and hormonal control of reproduction in elasmobranchs if more success is to be achieved in their reproduction in captivity. Knowledge gained from studies of the endocrine regulation of the reproductive cycle can be used to enhance the reproductive success of captive sharks, skates, and rays. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of a broodstock diet to improve developmental competence of embryos in European eel,Anguilla anguilla

We examined the effect of dietary arachidonic acid (ARA) and eicosapentaenoic acid (EPA) on the production of embryos and hatched larvae in the European eel, Anguilla anguilla. Two diets with high and intermediate levels of ARA and low and intermediate levels of EPA (Feed 1: ARA 1.9%, EPA 4.2%; Feed 2: ARA 1.2%, EPA 5.1% of total fatty acids) were tested against a commercial diet (DE: ARA: 0.5%, EPA: 8.2% of total fatty acids). After 24 weeks of feeding, ARA levels in the muscles and ovaries increased to 0.9% and 1.3% of total fatty acids, respectively, in Feed 1 and were significantly higher than in Feed 2 and DE. Female broodstock was not fed during hormonal treatment to induce vitellogenesis and ovulation. EPA levels in females fed the test diets decreased in the both muscle and ovary and were significantly lower in eggs from females fed Feed 1. The highest percentage of stripped females, producing viable eggs and larvae, were those females fed the highest dietary ARA levels (Feed 1). The level of lipid peroxidation products in eggs was similar among treatment, indicating that the lowest dietary levels of vitamin C and vitamin E were sufficient. In the unfertilized eggs, ARA levels were also highest (1.1% of total fatty acids) in the diet with highest ARA levels (Feed 1).     

药浴给药恩诺沙星及其代谢产物在欧洲鳗鲡体内的药代动力学研究

应用反相高效液相色谱法,研究药浴给药条件下,恩诺沙星及其代谢产物环丙沙星在欧洲鳗鲡体内的药代动力学.按10mg·L-1药浴给药后,恩诺沙星在欧洲鳗体内各组织器官中分布可用开放性二室模型来描述.血浆、肌肉、肝脏和肾脏中恩诺沙星达峰时间分别为44.27h、42.74h、50.69h、95.80h,以后开始缓慢下降,血浆、肌肉、肝脏和肾脏中代谢产物环丙沙星达峰时间分别为48.89h、55.34h、54.64h、100.0h.给药3个月后血浆、肌肉、肝脏和肾脏中的恩诺沙星浓度分别为0.0844μg·mL-1、0.09959μg·g-1、0.01242μg·g-1、3.7164u·g-1;恩诺沙星在血浆、肌肉、肝脏和肾脏中的消除半衰期(T1/2β)分别为908.07h、901.24h、59.32h、767.81h.鉴于恩诺沙星和其代谢产物环丙沙星在欧洲鳗鲡体内消除较慢,建议养成阶段不使用此药.     

Morphological and histochemical study of intestine in wild and reared European eel (Anguilla anguilla L.)

Diet-related differences between the ratio of intestine length to body size and the enzymatic activity in the intestinal tract of wild and reared European eel (Anguilla anguilla L.) were studied. Compared with reared eel, wild eel showed significantly shorter relative intestine length. For the purpose of histochemical examination, different parts (anterior, middle and posterior) of intestine proper were used. Activities of non-specific esterase, alkaline and acid phosphatase, and aminopeptidase were examined in each segment. All enzymes were present in the intestines of both wild and reared European eel. Fish from both groups showed similar enzyme distribution within the enterocytes, but distribution and intensity of enzyme activity along the intestine vary depending on the group. Generally, reared European eel showed highest enzymatic activity and wider distribution of enzymes throughout all parts of the intestine. These results suggest that different diets could be one of the reasons for observed changes.     

Daily rhythms of digestive physiology, metabolism and behaviour in the European eel (Anguilla anguilla)

Circadian rhythms are common in a wide variety of physiological processes. Our knowledge of biological rhythms in fish can be exploited to improve some key aspects of aquaculture such as feed optimization and fish welfare. The aim of this paper was to investigate daily rhythms in behavioural and physiological variables of the European eel. To this end, we first analysed the daily rhythms in locomotor activity measured by means of infrared photocells and feeding activity by means of self-feeders. The eels were then submitted to scheduled feeding (single meals once a day at a fixed time), and the levels of cortisol, glucose and digestive enzymes were analysed. Locomotor activity was predominantly nocturnal (63?% of daily activity occurring at night) with peaks located around light transitions, whereas feeding activity was less clearly defined. Cortisol and glucose showed daily rhythms, with acrophases located in the middle and at the beginning of the light phase, respectively, which should be carefully considered when using these parameters as welfare indicators. Significant variations were found during the day in acid protease levels, which increased in anticipation of mealtime. Taken together, these results describe for the first time a picture of the circadian physiology of the European eel, providing hints to improve feeding methods and welfare assessment.     

Histological and hormonal changes in the European eel (Anguilla anguilla) after exposure to environmental cocaine concentration

The aim of this study was the assessment of histological and hormonal changes induced in the European eel from environmental concentrations of cocaine. Silver eels were exposed to 20 ng L^?1 of cocaine during 50 days; at the same time, control, vehicle control and two post‐exposure recovery groups (3 and 10 days) were made. The general morphology of the skin and the intestine, and the plasma levels of prolactin, cortisol and dopamine were evaluated. In the skin, cocaine decreased the number and size of mucous cells, increased the thickness of the epidermis and altered the club cells and the basal lamina. In the intestine, cocaine increased the thickness of the epithelium and the number of mucous cells and reactivated the structure of the intestine and of the intestinal musculature. Moreover, cocaine increased plasma prolactin, cortisol and dopamine levels. These results suggest that cocaine induced histological changes, directly and/or through the hormonal changes observed. Considering the complex life cycle of the eel, the changes induced by cocaine in the skin, the intestine and the endocrine system could threaten the ability of the eel to successfully migrate and reproduce.     

孔雀石绿及其主要代谢产物在欧洲鳗鲡肌肉中的蓄积及消除规律

为了解孔雀石绿及其有毒代谢产物无色孔雀石绿在鱼体中的蓄积与消除规律,达到对孔雀石绿的禁用监控,本试验对初始体重为(12.42±2.18) g的欧洲鳗鲡进行0.1 mg·L-1 和0.2 mg·L-1 浓度(P1和P2组)孔雀石绿药浴24 h,再转移到清水中养殖120 d,采用高效液相色谱法测定肌肉组织中孔雀石绿及无色孔雀石绿的残留.在药浴过程中,鳗鲡肌肉组织中孔雀石绿平均含量不断升高,P1和P2组分别于药浴12 h和24 h达到最高值(720.5 ±192.6) μg·kg-1和(1404.8±421.9) μg·kg-1;在清水养殖过程中,孔雀石绿在鳗鲡肌肉中含量波动式下降,并于水浴2160 h (90 d)时两个处理组都低于检测限度.肌肉中所含无色孔雀石绿,在药浴过程以及清水养殖的开始一段时间内不断升高,P1和P2组分别于水浴的72 h和120 h达到最高值(960.1±251.0) μg·kg-1和(1 625.8±183.2) μg·kg-1,然后呈波动式下降,至实验结束(水浴120 d)时两个实验组肌肉中还有一定残留.结果表明,无色孔雀石绿的代谢消除时间较长,可以作为检测的标志物.另外,不同浓度的孔雀石绿在鳗鲡肌肉中的代谢规律相似,只是随药浴浓度升高,肌肉中孔雀石绿和无色孔雀石绿含量最高值出现时间有所滞后,以及消除时间相对延长.     

The home range and behaviour of yellow‐stage European eel Anguilla anguilla in an estuarine environment

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Estuarine and fluvial recruitment of the European glass eel, Anguilla anguilla, in an exploited Atlantic estuary

A glass eel fishery exists downstream of the Arzal estuarine dam in the Vilaine (Brittany, France). Catch statistics were collected between 1996 and 2000, and processed using a subsampling technique which allowed data from a reliable subsample to be extrapolated to the whole fishery. During the same period, glass eel migration into fresh water was monitored using a glass eel trap located on the dam – the upstream limit of the fishery. The analysis of glass eel biology and exploitation shows that the glass eel fishery is very intensive and that there was more or less no escapement during the fishing seasons studied. The proportion of the stock successfully migrating towards fresh water, as compared with the total catch is estimated to range between 0.3 and 3.9%. In such a fishery, the fishing effort affects the abundance. Consequently, the total catch has to be used instead of catch‐per‐unit‐effort to estimate abundance.     

孔雀石绿及其主要代谢产物在欧洲鳗鲡肌肉中的蓄积及消除规律

为了解孔雀石绿及其有毒代谢产物无色孔雀石绿在鱼体中的蓄积与消除规律，达到对孔雀石绿的禁用监控，本试验对初始体重为（12．42±2．18）g的欧洲鳗鲡进行0．1mg·L^-1和0．2mg·L^-1浓度（P1和P2组）孔雀石绿药浴24h，再转移到清水中养殖120d，采用高效液相色谱法测定肌肉组织中孔雀石绿及无色孔雀石绿的残留。在药浴过程中，鳗鲡肌肉组织中孔雀石绿平均含量不断升高，P1和P2组分别于药浴12h和24h达到最高值（720．5±192．6）μg·kg^-1和（1404．8±421．9）μg·kg^-1；在清水养殖过程中，孔雀石绿在鳗鲡肌肉中含量波动式下降，并于水浴2160h（90d）时两个处理组都低于检测限度。肌肉中所含无色孔雀石绿，在药浴过程以及清水养殖的开始一段时间内不断升高，P1和P2组分别于水浴的72h和120h达到最高值（960．1±251．0）μg·kg^-1和（1625．8±183．2）μg·kg^-1，然后呈波动式下降，至实验结束（水浴120d）时两个实验组肌肉中还有一定残留。结果表明，无色孔雀石绿的代谢消除时间较长，可以作为检测的标志物。另外，不同浓度的孔雀石绿在鳗鲡肌肉中的代谢规律相似，只是随药浴浓度升高，肌肉中孔雀石绿和无色孔雀石绿含量最高值出现时间有所滞后，以及消除时间相对延长。     

饲料添加剂喹乙醇引发欧鳗中毒的诊治报告

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恩诺沙星及其代谢物环丙沙星在欧洲鳗鲡体内的代谢动力学

采用高效液相色谱法,研究药饵口灌给药途径下,恩诺沙星及其代谢物环丙沙星在欧洲鳗鲡(Anguilla anguilla)体内的药代动力学。欧洲鳗鲡口灌给药恩诺沙星10 mg/kg后,其血浆、肌肉和肝脏中药物时量曲线关系符合一级吸收的二室开放动力学模型。恩诺沙星在欧洲鳗鲡不同组织中分布较广,血浆、肌肉和肝脏的Vd分别为6.362 L/kg、8.081 L/kg和15.870 L/kg;恩诺沙星在鳗鲡体内消除较慢,在血浆、肌肉和肝脏中的消除半衰期(tβ1/2)分别为161.10 h、333.21 h和611.26 h,总体清除率(CLs)分别为27.4 mL/(kg.h)、16.8 g/(kg.h)和18.0 g/(kg.h)。代谢物环丙沙星在鳗鲡血浆、肌肉和肝脏中药物水平的变化趋势与恩诺沙星基本相似,呈现出多峰现象,但3种组织中环丙沙星出现第一个药峰时间分别为给药后第24小时、24小时和12小时,3种组织中环丙沙星峰值水平肝脏中最高、肌肉中次之、血浆中最低,环丙沙星在肌肉和肝脏中的消除速率比较缓慢。鉴于恩诺沙星和其代谢物环丙沙星在欧洲鳗鲡体内消除较慢,建议养成阶段使用其他药物。     

Cutaneous myxidiosis in European eel,Anguilla anguilla (Linnaeus, 1758): histopathology,histochemistry and laminin immunohistochemistry

Histopathology, histochemistry and immunohistochemistry of the integument of European eel, Anguilla anguilla (Linnaeus, 1758), infected by Myxidium sp. are reported. Skin samples from affected and unaffected eels were dissected, formalin fixed, paraffin embedded, sectioned and stained with H&E, Periodic acid–Schiff's staining method, Alcian Blue 8 GX pH 2.5/Periodic acid–Schiff's and McCallum‐Goodpasture's Gram stain. Moreover, immunohistochemistry was performed using a primary polyclonal laminin antibody. Histologically, cysts (diameter 2–3 mm) were observed mainly under the scale pockets, encircled by a thin collagen layer, lined by elongated, flattened fibroblasts and containing bipolar, PAS‐ and Gram‐positive spores with opposite polar capsules. The epidermis stretched by the underlying cyst appeared dysplastic, thinned with a significant reduction in mucous cells number. Only inconsistent and aspecific inflammatory reaction was noted around the cysts at the dermis/epidermis interface. Intense laminin‐like protein immunolabel was documented in the plasmodial ectoplasm and related to host anergia. This was the first report of laminin immunolabel in a member of the Myxozoa. Epidermal dysplasia represents likely an aspecific response against the underlying tensile force exerted by the developing parasite cyst, while fibroblast and collagen encapsulation denote a parasite‐driven host response protecting, rather than harming, the encircled parasite.     

Effects of dietary fatty acid composition on metabolic rate and responses to hypoxia in the European eel (Anguilla anguilla)

European eels (Anguilla anguilla, L.) were fed on a commercial diet supplemented either with 15% by dry feed weight of menhaden oil (MO), an oil rich in highly unsaturated fatty acids of the n-3 series (n-3 HUFA), or with 15% by dry feed weight of coconut oil (CO), an oil composed primarily of saturated fatty acids (SFA). Following 90 days of feeding, the mean final masses of eels fed the two different oil supplements were similar, and higher than the mean final mass of a group fed the commercial diet alone. The diets created two distinct phenotypes of eels, distinguished by the fatty acid (FA) composition of their tissue lipids. Eels fed MO had significantly more total n-3 FA and n-3 HUFA in muscle and liver lipids than did eels fed CO, leading to higher n-3/n-6 and eicosapentaenoic acid/arachidonic acid ratios in the MO group. Measurements of O₂ uptake (M_O2) revealed that the MO group had a significantly lower routine metabolic rate (RMR) than the CO group. When exposed to progressive hypoxia, both groups regulated M_O2 at routine normoxic levels until critical water O₂ partial pressures that were statistically similar (9.62±1.08 kPa in MO versus 7.57±1.07 kPa in CO), beyond which they showed a reduction in M_O2 below RMR. The MO group exhibited a significantly lower M_O2 than the CO group throughout hypoxic exposure, but the percentage reductions in M_O2 below their relative RMR were equal in both groups. During recovery to normoxia, both groups exhibited an increase in M_O2 to rates significantly higher than their RMR. Throughout recovery, M_O2 was significantly lower in the MO group compared with the CO group, but the percentage increases in M_O2 relative to RMR were equal in both. During progressive hypoxia, neither group exhibited a marked ventilatory reflex response, both showed similar reductions in blood O₂ partial pressure and content, and similar increases in plasma lactate. The results indicate that, although the n-3 HUFA-enriched MO group had a significantly lower routine metabolic rate than the CO group, the difference in aerobic metabolism did not influence the European eel's homeostatic regulation of M_O2 in hypoxia.     

Protective immune responses of recombinant outer membrane proteins OmpF and OmpK of Aeromonas hydrophila in European eel (Anguilla anguilla)

Outer membrane proteins (Omps) of Gram‐negative bacteria have been proven to be efficient subunit vaccines against bacteriosis. In this study, OmpF and OmpK of Aeromonas hydrophila were expressed, and their immune protective effects in European eel (Anguilla anguilla) were evaluated. The genomic DNA of A. hydrophila 322A was used as a template, and two kinds of prokaryotic expression plasmids, pET‐32a‐OmpF and pET‐32a‐OmpK, were constructed. Recombinant OmpF protein (r‐OmpF) and r‐OmpK were purified and were proven to have antigenicity by Western‐blot analysis. r‐OmpF and r‐OmpK were used as immunogens to immunize European eel by intraperitoneal injection. The mRNA expression of 6 immune‐related genes (IgM, IL‐10, IRF3, IRF7, LysG4 and HexB) in the liver tissues of eels at 1 hr, 3 hr, 6 hr, 12 hr, 24 hr, 72 hr and 10 days postimmunization was analysed by real‐time PCR. At 30 dpi, the serum antibody response was measured by ELISA. Fish were attacked at 15 dpi by live 322A to assess the protective immunity of r‐OmpF and r‐OmpK. All the six tested genes responded to r‐OmpF or r‐OmpK vaccination at varying degrees. The serum antibody titre of r‐OmpF‐ and r‐OmpK‐immunized groups was 1:1,600 and 1:3,200 respectively. In addition, r‐OmpF gave 35.5% of the relative immune protection rate to European eels, while r‐OmpK gave 70.0%. By analysing the protective immunity and the regulatory role in the immune‐related gene expression of the two recombinant proteins that were studied, it was found that r‐OmpK was a potential vaccine candidate against A. hydrophila.     

Somatic growth, survival, feed utilization and starvation in European elver Anguilla anguilla (Linnaeus) under two different photoperiods

The aim of the study was to determine the effect of two photoperiod regimes under artificial conditions on growth performance and survival in the European eel Anguilla anguilla during the transition from glass eel to elver. The fish were held in 12-h-light:12-h-dark (12L:12D) and in continuous darkness (DD) in fed and fast trials lasting 80 days. Fed fish kept in the dark showed higher somatic growth, and a better feed conversion ratio, higher protein and lipid content, with significant differences between treatments. Dark environment increased the survival rate in comparison with fish exposed to 12L:12D, during which eels showed lower survival rates and greater variations in size. Fasted fish suffered loss of body mass in both photoperiods at the end of the experimental phase, but fish exposed to 12L:12D lost more body mass. These results indicate that the photoperiod is a key factor during the glass eel–elver stage, which may contribute to optimizing the early stages of eel culture.     

Effects of ammonia accumulation on metabolic rates and growth of European eel, Anguilla anguilla L., in relation to warmwater aquaculture

Abstract. Laboratory experiments on fingerling eels, Anguilla anguilla L., were carried out at high density (50gl¹) in fresh and sea water (30% salinity) at 25°C. The effects of reduced water exchange rates, leading to excretory ammonia accumulation, on feeding, assimilation, oxygen consumption, ambient pH and nitrogen excretion were studied. Estimates of growth rates were made. High ambient ammonia concentrations caused large and prolonged increases in post-feeding oxygen consumption, energy wastage and growth suppression. The main causes are suggested to be hyperventilation and neural hyperexcitability due to increases in blood unionized ammonia. The data obtained are used to predict minimum water exchange rates needed to prevent ammonia-induced growth suppression and to meet peak post-feeding oxygen demands.     

Effects of Temperature and Photoperiod on Reproduction of Female Yellow Perch Perca flavescens: Plasma Concentrations of Steroid Hormones, Spontaneous and Induced Ovulation, and Quality of Eggs

The involvement of photoperiod and temperature in the regulation of reproductive processes was investigated in female yellow perch. Initially, all fish kept indoors were exposed to the same water temperature (22°C) and photoperiod (15L:9D). By the end of August, following the first sampling, fish were submitted to different photothermal regimes. Group A₃ was maintained under photothermal conditions characteristic for southern Ohio. Group B₃ was submitted to a condensed light/temperature regime designed to accelerate photothermal changes. The mean gonadosomatic index in group A₃ gradually increased throughout the experiment. Gonadosomatic index in group A₃ was higher than that in group B₃ from February through April. The highest plasma concentrations of estradiol in group A₃ occurred in November and December and exceeded those in group B₃. Plasma concentrations of testosterone in group A₃ were highest in December and tended to be higher in October and April than in other months. There was no difference in plasma testosterone between groups A₃ and B₃ except in March when concentrations of this androgen were extremely high in group B₃. Ovulation occurred earlier in B regime fish in comparison to that of A regime fish. However, egg quality of fish from regime B was lower than that of fish from regime A. We conclude that the condensed photothermal cycle is not an entirely effective method of inducing out-of-season spawning in female yellow perch. These data suggest that although the compression of the photothermal cycle slightly accelerated spawning, it also caused disturbances in patterns and levels of plasma steroids, diminished ovarian and hepatic growth, and reduced the quality of eggs. Thus, temperature and/or photoperiod may have only a modifying effect on the onset of perch spawning, but these environmental cues seem to markedly influence earlier stages of gonadal growth and development.     

The effect of foraging and ontogeny on the prevalence and intensity of the invasive parasite Anguillicola crassus in the European eel Anguilla anguilla

Infection patterns of the invasive Anguillicola crassus nematode were investigated in a population of the European eel Anguilla anguilla where parasite invasion is very recent, Loch Lomond, Scotland. Intensity levels of the parasite were associated with differences in fish ontogeny and trophic ecology. Although eels foraged on both fish and invertebrates, individuals which were smaller and fed on invertebrates (>70% contribution to diet) were found to contain a greater number of swim bladder parasites compared to larger eel with a predominance of fish (>60% contribution) in their diet. Within affected fish, a significant negative relationship was found between fish length and parasite intensity, with smaller individuals having higher parasite intensity than larger individuals. This study indicates that food intake and infection risk are linked in this recently infected host–parasite system. From a management perspective increasing our understanding of how infection intensity and repeated exposure is linked to resource use in an ecosystem is important for the future management of this endangered species in Europe.     

The influence of phytoestrogens and oestradiol-17β on growth and sex determination in the European eel (Anguilla anguilla)

Under aquaculture conditions, European eels (Anguilla anguilla) produce a high percentage of males (80–95%) that normally stop growing at 100–200 g. Females continue to grow to 500–750 g and obtain higher market value. Therefore, increasing the percentage of females in a population would be beneficial to the culture of eels. The present study was carried out in order to examine the effect of oestradiol and phytooestrogens on sex differentiation and growth rate of eels. Juvenile European eels with undifferentiated gonads were fed pellets containing oestradiol‐17β (E2) or phytooestrogens for 100–150 days. Feeding E2 resulted in 50–61% increase in body weight compared with the control. Oestradiol‐17β and phytooestrogens both elevated significantly the percentage of females in the population. Feeding E2 at 20 mg kg^?1 feed resulted in 70% females, while lower concentration of E2 (2 mg kg^?1) resulted in only 30% after 100 days (Experiment 1). The same dose given for 150 days (Experiment 2) resulted in 88% females, indicating that both, the concentration and duration of E2 treatments had a significant effect on sex differentiation. Fish fed genistein at 2 mg kg^?1 for 100 days, resulted in 55% of females, but at a higher dose of 20 mg kg^?1 there were only 15% females. These results demonstrate that phytooestrogens can be used as alternatives to gonadal steroids for sex manipulation in eels, but the optimal concentrations and duration are still to be determined.