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1.
Abstract– Two almost eel-free lakes (339 and 299 ha respectively) in southeastern Sweden were stocked with French elvers in the autumn of 1980. The introduced eel stocks were monitored from the time of stocking and onwards using outlet traps equipped with fine-meshed screens and subsequently by test-fishing with long-lines and fyke-nets. Up to and including the spring run of 1994, more than 5,900 eels or about 2,600 kg were recaptured from one of the lakes, mostly as migrating silver eels. This means a recapture rate of about 11%. In the other lake most recaptures came from fyke-netting of the yellow eel stock. In this lake only 1.7% have been recaptured up to this point. These differences in yield and recapture rates from the two lakes are discussed in the context of lake productivity, growth rates, sex ratios, sizes of stocked elvers and size at silvering. In cconomic terms, the results from the higher-yielding lake indicate an excellent rate of profit. After approximately 10 years, the investment (cost of the introduced elvers) was paid back at a lending interest rate of 10%.  相似文献   

2.
Martin J, Daverat F, Pécheyran C, Als TD, Feunteun E, Réveillac E. An otolith microchemistry study of possible relationships between the origins of leptocephali of European eels in the Sargasso Sea and the continental destinations and relative migration success of glass eels.
Ecology of Freshwater Fish 2010: 19: 627–637. © 2010 John Wiley & Sons A/S Abstract – Little is known about the extent to which Atlantic eels coming from different European rivers converge on the same spawning site. Our aim was to evaluate the spatial homogeneity of eel spawning area(s) with an otolith microchemistry approach. This work compared the elemental signatures of otolith’s core region of Anguilla anguilla leptocephali caught in the Sargasso Sea in 2007 with those of glass eels and elvers sampled in European estuaries during 2006, 2008 and 2009. Using laser ablation inductively coupled plasma mass spectrometry, the same annular ablation trajectory along the first feeding mark was applied on otoliths of glass eels, elvers and leptocephali. The concentrations of thirteen isotopes in the otoliths of glass eels/elvers did not vary among three annual cohorts collected in eleven European locations. However, otolith elemental fingerprints of leptocephali differed significantly from glass eels otolith’s signature. Although the mechanisms that regulate the differences in trace element signatures among leptocephali and glass eels/elvers are unknown, we propose that the sampled glass eels/elvers were born in a spawning site or region where favourable transport and/or feeding conditions occurred. Conversely, the leptocephali may have been sampled in a less favourable region in the Sargasso Sea, with a low probability of reaching continental growth areas.  相似文献   

3.
Elvers and glass eels of Anguilla anguilla were fed diets containing two types of feeding stimulants (FS) that were based on processed marine (MBFS) and yeast proteins (YBFS). Elvers (1.5 ± 0.3 g) were fed seven diets (MBFS and YBFS diets at 20 g kg?1, 40 g kg?1 and 60 g kg?1 plus control) for 60 days. Glass eels (250 ± 100 mg) were weaned to 60 g kg?1 MBFS, 60 g kg?1 YBFS and control diets for 30 days. Diets containing 60 g kg?1 FS had a beneficial effect in terms of growth, homogenous size distribution and feed intake in elvers. Elvers fed 60 g kg?1 MBFS and YBFS diets grew 11.9% and 5.6% faster than the control group. No differences in growth and size distribution were detected in glass eels fed 60 g kg?1 MBFS and YBFS diets. However, FS affected the digestive system maturation; fish fed the 60 g kg?1 MBFS and YBFS diets showed higher and intermediate values in the specific enzyme activities in comparison with the control group. This study revealed that the incorporation of FS into a pelleted diet was beneficial on the overall performance of European glass eels and elvers. However, the observed results were different depending on the eel’s stage of development, as well as the type and inclusion level of the FS.  相似文献   

4.
  1. The European eel, Anguilla anguilla, is a catadromous and migratory species of commercial importance. Its complex life cycle results in its exposure to many risk factors, which have resulted in stock declines across all life stages since the 1970s.
  2. The temporal recruitment dynamics of juvenile eels (glass eels and elvers) were investigated in a small Mediterranean estuary (Sardinia, Italy). The composition of the population and the monthly and seasonal variations in the abundances of juvenile eels was assessed over 78 sampling events (from February 2017 to February 2018). Furthermore, the effects of abiotic variables on the abundances of glass eels and elvers were investigated using generalized additive models (GAMs).
  3. Glass eels had the greatest abundance during the winter months, whereas elvers had the greatest abundance during spring. Modelling revealed that the abundance of glass eels was mostly explained by the combined effects of water temperature (12.3–14.5 °C), tidal coefficient (40–110 cm), moon phase, season, and river mouth condition, whereas the abundance of elvers was associated with water temperature (14–21 °C), dissolved oxygen content (>7 mg/L), and season. These results suggest that the annual recruitment of juvenile eels occurs throughout the year, with clear seasonal migration dynamics.
  4. The use of multiple statistical approaches allowed us to identify the importance of several environmental variables in regulating the recruitment dynamics, providing useful information for conserving eel stocks through the restoration of the natural flow regime and the connectivity between freshwater habitats and the sea.
  相似文献   

5.
Abstract  The Lough Neagh eel fishery is the largest remaining commercial source of wild European eels. Following the pan-European elver crash in the 1980s, the numbers of elvers entering the Lough fell drastically, prompting the Lough Neagh Fishermen's Co-operative Society Ltd (LNFCS) to purchase additional glass eels from a UK distributor. LNFCS have continued to purchase glass eels, when market prices have been favourable, to supplement the natural glass eel input. This study assesses the impact of these stocked glass eels on the Lough Neagh yellow and silver eel fisheries with a predictive model based on natural and stocked glass eel input, effort and environmental variables. Despite the final models' limitations to assess conclusively the contribution of the additional purchased glass eels the models can be used cautiously to predict, in the short term, yellow and silver eel output. The models will require reviewing, on an annual basis, as further data become available.  相似文献   

6.
This study describes a mass marking method suitable for European glass eel Anguilla anguilla, avoiding osmotic shock and reducing fish stress. During a single day, 360,000 glass eels intended for a stocking operation were bathed into an alizarin red S (ARS) solution, at a density of 346 ind.·l?1 before being released into a freshwater marsh along with unmarked glass eels. After 15 days, examination of marked and unmarked eels kept in enclosures in the marsh showed 100% of otoliths had been successfully marked and that no excess deaths related to marking process had occurred. Seven months after stocking, results from biometric measurements and otolith analysis, carried out on a sample of 53 elvers caught by electrofishing and belonging to the size class of the 0+ cohort, suggest that: (i) the proportions of marked and unmarked remained unchanged, hence suggesting that the marking process had not caused excess mortality, (ii) there was no difference in length, body mass or condition factor between marked and unmarked individuals, demonstrating that marking had caused no harmful effect after 7 months, and (iii) ARS marks in otoliths remained clearly visible. The benefits of this ARS mass marking technique are discussed through a stocking operation.  相似文献   

7.
There is expanding interest in the culture of the Australian shortfin eel Anguilla australis Richardson; however, there is a lack of fundamental biology and husbandry information necessary to further develop an industry within Australia. The present study was undertaken to gain a preliminary understanding of basic husbandry requirements for rearing of juvenile A. australis (glass eels and elvers) in tanks and earthen ponds. Newly caught glass eels were successfully acclimated to culture conditions. During tank culture trials, specific growth rates (SGR) and survival rates ranged from ?2.1 to 2.8% day?1 and 52% to 100% respectively. Glass eels weaned onto a commercial eel diet exhibited a significantly greater SGR and survival rate than those weaned onto a commercial trout diet. Glass eels weaned onto an eel diet over a 15‐day period grew slightly faster than eels weaned over a 5‐day period, but survival rates were not significantly different for each treatment. SGRs (up to 2.8% day?1) were significantly higher for glass eels fed at 9 and 12% day?1 than at 6% day?1. Stocking densities between 2.5 kg m?3 and 30 kg m?3 did not influence either SGR or survival rates. SGRs were significantly higher for glass eels cultured at 25 °C than at lower temperatures. During pond culture trials, SGRs and survival rates ranged from 1.36 to 1.65% day?1 and 39% to 77% respectively. The SGR and survival rates of juvenile eels stocked into ponds receiving supplementary feeding with a commercial eel diet were not significantly different to those of eels stocked into ponds that did not receive supplementary feeding.  相似文献   

8.
In a controlled experiment, elvers (Anguilla anguilla L.) were reared for 137 weeks at 17, 20 and 26°C. Most eels with macroscopically sexable gonads were males. The proportions of females were 14% of sexable individuals at 26°C and 7–8% at 17 and 20°C. During the first 15 weeks, 20–50% of initial numbers were lost, but this early mortality was not significantly size selective. In spite of a long term experiment, a significant number of the survivors never attained a sexable size. Nongrowers (7–9 cm) were still alive nearly three years after being caught as glass eels. Among the earliest fast growers, 5% females, or less, were found. The proportion of females increased in later grading groups, but the pattern of increase did not indicate that males and females have separated mean ranks in a fixed growth hierarchy. Water temperature influenced observed sex ratios, but probably not through direct influence on the sex differentiation. Some alternative hypotheses, dealing with population density and individual growth status, are discussed.  相似文献   

9.
Abstract. In four experiments, performed at the Agricultural University, Wageningen and the Netherlands Institute for Fishery Investigations, the effects of attractants on feed acceptance and growth of glass eels, Anguilla anguilla L., were studied. The results show that extracts from natural food or a mixture of synthetic amino acids improve acceptance of a trout fry crumble at first feeding of glass eels. Overall results can be greatly improved by initiating the feeding behaviour of the fish by feeding cod roe for the first few days. The results also demonstrate a strong effect of the feeding level on feed acceptance. At relatively high feeding levels no significant effect of attractants could be detected.  相似文献   

10.
This study was undertaken to determine the influence of orally administered 3,3,5-triiodo-L-thyronine (T3) or 17--methyltestosterone (MT) on growth and body composition of the eel (Anguilla anguilla L.) during the glass stage.Elvers receiving 20 or 40 ppm of T3 in the food weighed significantly more (P < 0.05) than controls. However, after 61 days of treatment a dosage of 60 ppm was not efficacious.Terminal percentages of body protein were significantly lower (P < 0.05) in elvers that received 20 ppm or 40 ppm T3 in their diets, than in the control. Crude body fat content was higher (P < 0.05) in elvers receiving 20 ppm (29% fat) or 40 ppm (28% fat), than in the controls (26% fat). Compared to the control, diets containing T3 at 20 or 40 ppm increased the body glucose concentration.Glass eels fed a diet containing 1 or 10 ppm MT grew significantly more slowly (P < 0.05) than the controls.Total body protein content was higher (P < 0.05), but total body crude fat content was lower (P < 0.05) in elvers fed a diet with 1 or 10 ppm MT compared to the controls. Total body glucose concentration of elvers administered 10 ppm MT was significantly lower (P < 0.05) than that of the control groups.  相似文献   

11.
Olfactory attractiveness and gustatory palatability of different materials of potential importance in first-feeding of young eels, Anguilla anguilla (L.), were examined using a novel electromechanical device which was developed for rapid screening. Comparisons were made between non-feeding glass eels and elvers that had commenced feeding on a commercial formulated granule diet. Preparations of tubificid worms, earthworms (Eisenia foetida), cod roe, beef liver and potentially stimulatory chemicals were tested. Invertebrate-derived foodstuffs and combinations of amino acids, inosine 5′-monophosphate and glycine betaine were found to be more attractive than vertebrate foodstuffs pre-weaning. Attractiveness and palatability, especially of granules formulated for eels, were strongly influenced by learning after feeding had commenced. Implications for weaning of glass eels in aquaculture are discussed. Further uses of the rapid-screening device are discussed.  相似文献   

12.
The suitability of a dry commercial expanded diet for the early rearing of newly-caught glass eels without weaning was investigated.

During a 104-day period, suitable feed particle sizes were determined for various sizes of fish, and growth and survival monitored. All mortalities, which totalled 28% of the initial population, occurred during the early stages of the experiment, suggesting that they were fish which either did not accept, or were unable to utilise, the diet given. No cannibalism was seen at any time. Overall growth rate and food conversion averaged 2.03% of bodyweight/day and 2.1 respectively. Selected, faster growing fish (35% of the stock) showed an average growth rate of 3.41%/day and a food conversion of 1.47.

The differences between the results obtained with the diet used and previously published data are discussed.  相似文献   


13.
为了解舟山群岛外海域鱼类资源状况,于2018年4月(春季)和10月(秋季)在舟山群岛外海域进行的渔业资源调查,用得到的数据分析了鱼类种类组成、优势种、群落结构及生物多样性。结果显示:(1)舟山群岛外海域鱼类有106种,隶属于12目47科80属;(2)本次调查鱼类种类数春季为63种,秋季为85种,总体与历史调查结果相比春季明显减少,而秋季却略有增加;(3)2个季节的鱼类优势种更替明显,春季优势种为黄鮟、日本红娘鱼和细条天竺鲷,秋季优势种为细条天竺鲷和日本发光鲷;(4)鱼类生物多样性指数值为秋季大于春季,春、秋季均匀度指数(J')对比多样性指数(H')和丰富度指数(D)都较小,且春、秋季生物多样性指数值基本都是随着水深的增加而增加,均以80 m以上水深区间较高;(5)通过聚类分析与非度量多维标度排序分析可得,春季在35%的相似水平上分为3个群落,秋季在45%相似水平上分为2个群落,秋季物种相似度比春季高,春季在生物量和丰度水平上均比秋季低。研究表明,舟山群岛外海域的春季鱼类群落结构可能处于未受干扰状态,秋季鱼类群落结构可能处于严重干扰状态。  相似文献   

14.
Abstract. Details of mean annual slocking rate and catch of eels in a random sample of 68 Polish lakes over a period of 36 years are presented. Multiple correlation and curvilinear regressions are used to assess the effectiveness of stocking. Maximum stocking rate of 275 elvers/ha/year and maximum catch of 5.2 kg/ha were determined. Yields per recruit were highest in the lakes in which the greatest catches of other fish were made and stocking was most effective in lakes of depth less than 5 m.
The theoretical maximum catch of 5.2kg/ha was very much less than maxima observed elsewhere. Two possible contributory factors are the Polish practice of using relatively large-meshed seines for fishing, permitting the escape of eels of less than 50cm and the relatively small number of potential competing fish species in fisheries such as that of Lough Neagh in Ireland.  相似文献   

15.
Abstract. Myxidium giardi was found in wild and cultured eels. The prevalence rate in elvers was 77% in the River Torridge (Devon), 80% in the River Parrett (Somerset) and 90% in the River Ouse (Yorkshire). Adult eels from the River Ouse had a prevalence rate of 53%, Cultured fingerlings and adults had a prevalence rate of 60% and 1% , respectively. There was an apparent age-related pattern in the organ location of the histozoic trophozoite: an initially high prevalence of kidney trophozoites which gradually decreased with age; in the gills of elvers there was a low prevalence of histozoic trophozoites which increased in the adult stage. Histozoic trophozoites were also found in the stomach and intestine of elvers and fingerlings. A qualitative estimate of trophozoite numbers in each organ of elvers is given. The coelozoic trophozoite of M. giardi in the gall bladder of elvers and fingerlings is also described for the first time.  相似文献   

16.
Abstract. A technique which uses electrodes at the mouths of meshless water outlets of fish tanks is described. The electrical field generated by the electrodes was effective in discouraging fish from approaching the open outlet, and allowed free discharge of debris-laden water without the usual blockage of the outlets by faeces and uneaten food. The system was found to be particularly effective for the rearing of eels (from the glass eel stage on) which typically cause a rapid deterioration in water quality due to their feeding behaviour. It was also found very useful for rearing other fish larvae in tanks.  相似文献   

17.
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.  相似文献   

18.
The effects of changes in the feeding regime on growth rate, body composition and fatty acid content of body lipids were monitored during the production cycle of European eels (Anguilla anguilla) in a fish farm, from elvers to commercial size (> 100 g).A high variation in growth rate obliged periodic grading. The fat content in the body of the eels notably increased over the study period in a direct relationship with size. At commercial size, a certain degree of sexual dimorphism was apparent, as were differences in dorsal coloration. At this stage, females were clearly larger than males and had a greater amount of body fat.Changes in dietary lipid composition (moist natural food, pellet foods with low and high fat content) influenced fatty-acid composition of body and muscle lipids. No differences between sexes were recorded in this respect. In general, indices of the nutritional quality of body lipids decreased progressively (in terms of the ratio between saturated, on the one hand, and mono- and polyunsaturated, on the other). However, the high fat content of the eels' edible fraction provides an equally high amount of the strongly recommended highly unsaturated fatty acids of the 3 series (HUFA3). © Rapid Science Ltd. 1998  相似文献   

19.
The ideal water conditions for maximizing the performance of the nursery culture of glass eels harvested from the wild for aquaculture need to be determined for the New Zealand shortfin (Anguilla australis) and longfin (Anguilla dieffenbachii) eels. This study determined the survival and growth of glass eels reared under different temperature and salinity conditions in the laboratory. The growth and survival of shortfin and longfin glass eels reared in salt water (35‰) maintained at 25 °C was examined over 84 days from capture. The mean specific growth rate (SGR) was higher in shortfin [2.30±0.29% body weight (b.w.) day?1] than longfin glass eels (1.52±0.06% b.w. day?1), and survival was also higher in shortfin (76.0±4.16%) than for longfin glass eels (28.7±6.36%). A second experiment identified the effect of salinity (0, 17.5‰ and 35‰) and temperature (17.5 and 26.5 °C) on the acclimation, growth performance and survival of shortfin and longfin glass eels over a period of 84 days from capture. There was no incidence of mortality for either shortfin or longfin glass eels reared across all salinity treatments (0‰, 17.5‰ and 35‰) at 26.5 °C, while survival of shortfin and longfin glass eels reared at 17.5 °C was the highest in 17.5‰, followed by 35‰ and 0‰ treatments. Both temperature and salinity affected the SGR of shortfin glass eels, with the highest SGR observed for shortfin glass eels reared in 0‰ water maintained at 26.5 °C. In longfin glass eels, salinity alone had an effect on the SGR, with the highest SGR observed in glass eels reared in 0‰ water regardless of the water temperature (17.5 and 26.5 °C). In addition, the adaptability of glass eels to salinity was evaluated from the development and the physiological responses of gill chloride cell (CC) morphology. The number and size of CCs increased significantly with increasing salinity in both shortfin and longfin eels.  相似文献   

20.
乐清湾口海域春秋季鱼类群落多样性研究   总被引：1，自引：0，他引：1  
为研究乐清湾口海域鱼类群落结构动态变化趋势和渔业资源现状,对该海域鱼类物种组成、种类数、多样性等群落结构特征进行调查分析。共鉴定出鱼类49种,隶属于10目26科39属。结果显示,春季物种数较秋季少,春季在瓯江口水域物种明显较少,秋季物种数空间分布大致为东西走向;春季种类重量多样性低于秋季,但尾数多样性高于秋季,鱼类种类数与多样性指数之间有较强的相关性。研究表明,乐清湾口海域的鱼类种类类型以近岸河口性鱼类为主,且大多为广温、广盐性种类;该海域位于河口,受瓯江径流影响较大;受地理位置和水文环境影响,该海域暖水性种类较多;种类数平面分布特征主要是春季受瓯江径流淡水水团影响,而秋季受交汇水团影响,物种丰富;两季鱼类多样性不同,是因为鱼类个体大小、数量随着季节的变化而变化。  相似文献   

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