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1.
Japanese eels (Anguilla japonica) perform large‐scale oceanic migrations between their spawning ground and growth habitats in continental waters during life history. However, between these migrations, they spend most of time in growth habitats such as rivers. To investigate the diel and seasonal activities, homing behaviour and home range of yellow‐phase Japanese eels in the lower reach of the Tone River, we tracked them throughout a year using a fine‐scale positioning system (VPS) based on acoustic telemetry. The tracked eels were generally nocturnal, but not exclusively. They were mainly mobile from spring to autumn, with little or no activity observed during winter. A transport‐release experiment showed that most eels returned to their original capture area within 13 days after release. The eels had very small home ranges (mean ± SD = 0.085 ± 0.068 km2), core areas (0.014 ± 0.014 km2) and linear home ranges (744 ± 268 m). They also tended to be distributed on one particular side of the river (right or left bank) and in one particular shore type (revetment or vegetation), rarely moving from one to the other. This study provides evidence for nocturnal, dormancy, homing behaviours, limited habitat use and small home range size in Japanese eels. The eels clearly showed strong fidelity to a “familiar” site, which contrasts with the long distances travelled during upstream and downstream migration phases in the river, and during spawning migrations in the ocean.  相似文献   

2.
Large‐scale habitat use and movements of yellow American eels (Anguilla rostrata) from the St. Lawrence River were examined using acoustic telemetry from early summer to late fall in 2010 and 2011. Sixty‐seven eels were tagged, and their passage or presence was recorded using fixed acoustic arrays covering a 400 km distance along the St. Lawrence River and Estuary. Sixty‐four per cent of the 67 tagged eels were detected. Most eels were detected at only one array; the closest to their release location and at several occasions during the tracking period, suggesting a high proportion of freshwater residency in the upstream part of the St. Lawrence River. Downstream movements towards the brackish estuary (63–418 km distance) were demonstrated for 16.4% of the eels, particularly for those caught at the most downstream site that is close to the brackish estuary. Our results strongly suggest a lower activity of freshwater resident yellow eels during summer, a behaviour that may be related to day length, which defines time available for their nocturnal foraging. Indeed, yellow eels were detected primarily at night; no effect of moon phase was revealed. Movements in the vicinity of arrays (up to 116 km in the fluvial estuary) were suggested and smaller‐scale movements within Lac St. Louis were demonstrated, highlighting a yellow‐eel home range far more extensive than previously reported in smaller systems. Evidence for within‐season homing and site fidelity is also reported.  相似文献   

3.
Meagre (Argyrosomus regius) is an emerging species in aquaculture considered a locally absent species in the Western Mediterranean. Little is known about meagre escape incidents from farms. To evaluate escape impacts and develop mitigation measures, knowledge about the behaviour of escaped meagre is necessary. In this study, a rapid dispersion of escaped meagre was observed following a simulated escape incident in a coastal Mediterranean farm, using acoustic telemetry (acoustic tag: AT) and mark‐and‐recapture techniques (external tag: ET). A small proportion of AT meagre (22.7%) remained within the farm boundaries 24 h after the simulated escape. A total of 84 meagre (9.2%) were captured by local trammel netters nearby the farm facility within the first 48 h after escape. Only two AT individuals (15.3%) were detected by acoustic receivers located in coastal areas within 2 days after dispersal from the farm and eight ET meagre (0.8%) were recaptured along the shoreline during the first week. Two AT individuals (15.3%) were considered to be dead by predation few hours after escape. The rest of the AT individuals (N = 6, 46.2%) left the facility alive, and they were never detected by receivers nor reported back by fishermen. Thus, our results highlight the necessity of establishing escape mitigation strategies at Mediterranean fish farms, i.e. recapture programmes 24–48 h after the escape incident in collaboration with local fishermen, to diminish potential impacts related to meagre escapees.  相似文献   

4.
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5.
Downstream passage of European eel Anguilla anguilla (L.) in catchments with pump(s) for water level management is a major concern. Catchment‐wide acoustic telemetry revealed silver eels quickly migrated downstream through unobstructed reaches (n = 12; mean ± SD = 17.9 ± 1.9 km/day). Fourteen of 17 acoustic‐tagged eels detected at the pumping station (82.1%) retreated back upstream and ten (58.8%) passed through pumps after delays (9.5 ± 11.0 days). Multi‐beam sonar imaging across the intake screen (55‐mm gaps) revealed that peaks in migration occurred during the nights preceding the new moon but 76.7% retreated back upstream. All passive integrated transponder (PIT)‐tagged eels recaptured (n = 56) downstream of a large (2.23‐m diameter) mixed flow pump survived but 96.5% had minor injuries, reduced physical condition and/or abnormal behaviour. By contrast, 64.7% of PIT‐tagged eels recaptured (n = 17) downstream of a small (0.8‐m diameter) axial flow pump died. No acoustic‐tagged eels that passed through the small axial flow pump (n = 10) performed onward migration at sea, unlike “control” eels released downstream (n = 11). This evidence may help develop effective remediation measures, such as operational changes, to maximise escapement of catadromous eel species at pumping stations.  相似文献   

6.
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.  相似文献   

7.
Over a period of 34 years (1954–1987), a total of 11.9 million glass eels were stocked all over Austria to improve the yields of commercial fishermen and to make the lakes more attractive for anglers. Nearly half (48%) of the imported glass eels were introduced into natural, previously eel‐free Alpine lakes until stocking ceased in 1988. Twenty‐five years later, their occurrence could be verified in 56% (N = 22) of the Austrian Alpine lakes larger than 50 ha and mean body length had increased to 66 cm. Eels from seven selected Austrian Alpine lakes exhibited a yearly mean increase in length between 0.6 and 1.5 cm, indicating a comparatively poor growth compared with the majority of eel populations from within their natural distribution range. At the same time, high expectations in developing a flourishing eel fishery were not met. In all but one lake, the harvest remained below 3% of the total yearly catch and salmonids remained the dominant target species. During peak harvest in the 1980s, it exceeded 8% in mesotrophic Wallersee (2600 kg). Simulations of stock development indicated that the yield could have been improved, but contrary to earlier expectations eels never became important for local cuisine and catches remained too low for the development of a profitable export business. On the other hand, eels may have contributed to the loss of small‐bodied fish taxa.  相似文献   

8.
To learn about the relationships between feeding and growth of temperate eels in freshwater and brackish water habitats, we analysed 533 yellow‐phase Japanese eels Anguilla japonica collected in both types of habitats in southeastern Japan. Because male eels were very rare in each habitat (FW, N = 1; BW, N = 20), characteristics of female eels were compared between the different habitats. Annual food consumption was evaluated with the consideration of instantaneous food consumption and annual activity period. Stomach fullness index (stomach content weight/body weight) was used as an indicator of instantaneous food consumption. The ratios of number of months with eel catch to those when eel sampling was conducted were used as an indicator of activity period. Female yellow eels tended to be older and slower growing in fresh water (N = 78; age, mean ± SD = 7.9 ± 2.4 years; growth rate, 59.8 ± 14.0 mm year?1) than in brackish water (N = 229; age, 5.5 ± 1.8 years; growth rate, 90.1 ± 24.4 mm year?1). Irrespective of sex, yellow eels in brackish water had a higher stomach fullness index and a greater ratio of months with eel catches, indicating greater annual food consumption by brackish water eels. These results indicate that greater annual food consumption contributes to the greater growth rates of Japanese eels in brackish water habitats.  相似文献   

9.
Current knowledge about the downstream migration of sexually mature European eels (Anguilla anguilla) remains incomplete, particularly in still water habitats such as lakes and wetlands subject to water level management. However, for the management of this endangered species, it is important to understand migration dynamics, and contribution to the breeding stock. This study aimed to assess the parameters that trigger and guide the migration of silver eels in the largest floodplain lake and associated wetlands in France (the sluice regulated Grand‐Lieu Lake). A telemetry survey of 50 acoustic and PIT‐tagged female silver eels was performed during the 2015–2016 migration period. We deployed a novel telemetric approach, using receivers to delimit several restricted virtual boxes to determine the instantaneous location of individuals and to transform simple discrete telemetric data into presence/absence data. The low numbers leaving the lake centre are probably explained by the lack of orienting water flows or other environmental clues, but whilst the fate of 34% (17/50) of the tagged eels is unknown, 18% (9/50) were caught by commercial fishermen. Modelling showed that detections were not clearly associated with environmental factors typically involved in riverine migrations (e.g. current velocity, atmospheric pressure and temperature) but they were particularly associated with higher and increasing water levels and, for eels exiting the lake, a sharp increase when sluice gates were opened to an effective gap of >75 cm. It is concluded that management of water levels and sluice gate opening during the migration period might aid escapement of silver eels.  相似文献   

10.
Due to a recruitment decline of more than 90% in 30 years, the European eel (Anguilla anguilla L.) has been classified by IUCN as critically endangered. Although the species has been studied intensively to obtain knowledge to improve management, studies about the resident yellow stage are relatively scarce. In this study, 52 large female yellow eels were tagged with acoustic transmitters in a Belgian polder system and tracked by a network of 23 automatic listening stations. We studied both circadian and seasonal movement patterns and the effect of environmental variables on these patterns. Large female yellow eels were most active at night in late summer and early autumn. A generalised linear mixed model showed that their movement is only slightly influenced by environmental variables. Moreover, as yellow eels show high site fidelity (i.e., the majority was detected only in the habitat type of their catch‐release location), they do not encounter many human‐induced connectivity problems in polder systems, which makes these systems highly suitable as eel growth habitat. These results can contribute to an effective eel management regarding habitat protection and restoration.  相似文献   

11.
Sea cucumbers are free of protective exoskeleton and capable of autolysis under stress conditions. The live transport of small‐size juveniles to grown‐out sites induces hypoxia and congesting stress. The transport process is essential to production of outdoor healthy seedlings. Here, we evaluated the effects of damp transport and water transport on Apostichopus japonicus, an economic species inhabiting along the Asian coast. The survival after transport and immune performance of small‐size juveniles (0.05–0.1 g of immersed weight) were monitored during distinct duration of transport (1, 3, 5, 8 and 12 hr). The results revealed that there were no significant differences between the two transport systems within 5 hr. Given the survival for recovery of 48 hr and responses of immune enzymes and catecholamines during transport, water transport was less detrimental to sea cucumbers than damp transport when the transport duration was less than 8 hr. Once the duration prolonged to 12 hr, these immune parameters changed irregularly and the survival declined drastically. Water transport with a notably higher survival for juveniles was the more appropriate manner for long‐time transport. These findings provide insights into long‐term transport of small‐size A.  japonicus juveniles and might be beneficial for production of ecologically healthy seedlings.  相似文献   

12.
Monitoring of yellow‐phase and silver‐phase Anguilla anguilla during their continental life history is necessary for evaluation of stock recovery measures. Eel population data for an Irish lake (Lough Sheelin) were compiled for the period 1993–2014. Catch data from 2009 to 2014 provided minimum estimates of recent silver eel production ranging annually from 0.79 to 1.84 kg/ha. Long‐term changes in yellow eel abundance and silver eel size structure were assessed as part of a fishery monitoring programme. Yellow eel catch per unit effort (CPUE) in the lake (from longline surveys) was considerably higher in the 1990s (52.2–62.1 eels/100 hooks) than 2002–2008 (1.9–15.8 eels/100 hooks). Conversely, during 1993–2014, the mean size of silver eels migrating from the lake increased significantly (p < .001), from 659 mm to 838 mm. The results suggest that in the absence of direct yellow eel abundance data, interannual variation in silver eel size structure may be a useful monitoring tool for local eel stocks as part of Eel Management Plans (EMP's).  相似文献   

13.
Abstract – Yellow‐phase Japanese eels (Anguilla japonica) were investigated in the Hamana Lake system, Japan, from 2003 to 2004 to understand how their demographic attributes vary within the lake system. A total of 779 yellow eels were collected during sampling in two inlet rivers and two brackish/saltwater lakes within the lake system. Female eels predominated, constituting 84% of the 75 sex‐determined eels in the river, and 50% of the 151 sex‐determined eels in the lakes. Total lengths (TL) of all eels examined ranged from 54.2 to 715.0 mm (mean = 320.4 ± 145.4 SD). In the inlet river, the TL of eels showed a significant positive relation with the distance from the river mouth. The estimated relative abundances of eels ranged from 0 to 1.8 eels·m?2 effort (mean: 0.3 ± 0.41) in the river and was negatively correlated with the distance from the river mouth. This suggested that larger eels might tend to be distributed at lower abundances in upstream reaches of the river. Mean age of yellow eels determined by their otolith annuli was younger in the lake (N = 117, 3.3 ± 1.4 years) than in the river (N = 214, 4.3 ± 1.7 years). Growth rate was higher in the lake than in the river at age 1–2 years (131.9 and 104.4 mm·year?1, respectively). The results of this study suggest that, although Japanese eels can adapt to various types of environments, significant differences can occur in population structures and growth patterns among habitats.  相似文献   

14.
A 30‐day experiment was conducted to investigate the effects of long‐term low‐salinity stress on the growth performance and osmotic related chlorine ion channel ligand regulation: gamma‐aminobutyric acid (GABA) content and GABAA receptor‐associated protein (GABARAP) expression in Portunus trituberculatus. The salinity levels of both the control group and the experimental group were 30 and 12 psu respectively. After rearing for 30 days, the specific growth rate and survival rate were compared between the two groups, and salinity 6 psu was used to test the salinity tolerance. The results were as follows: (a) Both the specific growth rate and survival rate were significant lower in the experimental group (p < 0.05) after 30 days; (b) After challenge with salinity 6 psu for 72 hr, the crabs of experimental group had a 100% survival rate, whereas the crabs of the control group were all dead within 48 hr; (c) The content of GABA and the gene expression level of GABARAP in experimental group were significant different from control group (p < 0.05) after challenge via salinity 6 psu. In the control group, the GABA content increased rapidly from 9.96 ± 2.09 to 42.00 ± 5.94 µg/g; however, in the experimental group, it only increased to 27.82 ± 2.55 µg/g; the gene expression of GABARAP in the experimental group increased to the maximum at 24 hr, then decreased and stabilized at 48 hr, suggesting that GABA and GABARAP were trigged during the early stage of low‐salinity stress resistance.  相似文献   

15.
Viral infections have been suggested to play a role in the decline of the panmictic population of the European eel (Anguilla anguilla). However, despite the importance of knowledge about pathogenic eel viruses, little is known about their spread in the wild European eel population and only a few eel pathogenic viruses have been described so far. In this study, we aimed to investigate the health status of the A. anguilla stock in North Rhine Westphalia (NRW) State of Germany. For this purpose, we examined tissue samples of 16 elvers, 100 yellow eels and 6 silver eels, sampled from the rivers Rhine, Lippe and Ems. Virus detection was performed via a combination of cell culture and PCR. Next to the detection of frequently encountered pathogenic eel viruses (anguillid herpesvirus 1 and eel virus European X (EVEX)), we isolated the eel picornavirus 1 (EPV-1) from tissue of yellow eels and elvers and demonstrate the distribution of EPV-1 in wild eel population in NRW.  相似文献   

16.
This study compares diagnostic imaging tools in detecting the parasitic swimbladder nematode Anguillicoloides crassus in Anguilla anguilla (L.) and focuses on ultrasound in an attempt to develop a non‐destructive, field diagnostic test. Ultrasound use could allow the parasite to be diagnosed without decreasing the number of critically endangered European eels through post‐mortem. In the preliminary study, eels were examined with computed radiography, computed tomography, magnetic resonance imaging, 14 MHz high‐end ultrasound and 5 MHz low‐end portable ultrasound, and the results were compared with post‐mortem findings. This ultrasound scanning technique did not produce any promising results. A second batch of eels was examined using the same high‐end and low‐end ultrasounds, but employing a different scanning technique and comparing the results with post‐mortem. This second study, scanning along the midline from below, allowed for the detection of anomalies associated with moderately infected animals. None of the eels used in this study were severely infected; thus, no conclusions can be made regarding the use of ultrasound in those animals. Overall, it was found that none of the techniques were useful in diagnosing mildly infected individuals; therefore, no single diagnostic imaging tool is sensitive enough to replace post‐mortem for definite diagnosis.  相似文献   

17.
Competitive shore‐based sport fishing is a popular recreational activity in the Maltese Islands. However, prior to this study, no scientific research surveys had been carried out during sport fishing competitions to investigate catches. Collaboration with Maltese sports fishermen was developed to target sustainable management. Recreational fishing catches were recorded between July 2012 and December 2015 by means of 1,633 roving‐access creel surveys, conducted during 79 sport fishing competitions, totalling a fishing effort of 7,548 hr. A total of 29,916 fish belonging to 80 species from 26 different families were caught at a mean catch‐per‐unit‐effort (CPUE) of 4.16 fish angler/hr (SD ± 3.79) and 0.18 kg angler/hr (SD ± 0.17) but with seasonal variation. Catch‐and‐release practices were implemented by all Maltese sport fishing clubs, however, the mean mortality rate stood at 35.5% (SD ± 42.1), indicating that more effort is required to improve survival of fish. The study outcomes provide conservation recommendations.  相似文献   

18.
Goldfish (Carassius auratus) was one of the first fishes to be domesticated and has been widely introduced across the globe, but is now considered one of the world's worst invasive aquatic species. Surprisingly, there is a dearth of information on its spatial and temporal movement patterns, which hampers the development of effective control programmes. We examined the movement patterns of an introduced population of C. auratus in a south‐western Australian river using passive acoustic telemetry. The study population had a high residency index within the array (i.e. proportion of all days at liberty that, on average, each fish was detected by a receiver) with fish being detected on 64% of days. The individuals were also reasonably mobile, travelling a mean of 0.30 km (linear river kilometres).day‐1 within the array, and one fish moved 231.3 km over the 365‐day study period (including 5.4 km in a 24 hr period). Importantly, C. auratus displayed significant seasonal movement patterns including a clear shift in habitats during its breeding period with most mature individuals being detected in an off‐channel wetland during that time. The results of this study strongly suggest that C. auratus undertook a spawning migration into a lentic habitat. These results have important implications for developing control programmes for the species, such as targeting connections to off‐channel lentic systems during its breeding period.  相似文献   

19.
The Mediterranean spearfish (Tetrapturus belone) is one of the least‐studied istiophorid billfishes, with little known of its biology, ecology, and behavior. To assess the species’ movement and thermal niche, we analyzed telemetry data from, to our knowledge, the first and only Mediterranean spearfish ever outfitted with a pop‐up satellite archival transmitting tag. Throughout a 29‐day deployment during July and August 2015, the fish travelled in Italian waters of the Tyrrhenian and Ligurian Seas, spending on average 93% of each 24‐hr period above 30 m and exhibiting a diel activity pattern comprised of daytime vertical movement and nighttime near‐surface residency. The preferred thermal niche was 26–28°C, but the spearfish experienced temperatures as low as 14.2°C during descents. Vertical distribution was limited throughout the deployment with more time spent at depth in areas where the thermocline was comparatively deeper and weaker, consistent with habitat compression experienced by other billfishes.  相似文献   

20.
Overwintering dormancy behaviour was studied in female silver eels in Lake Mälaren in Sweden between 2008 and 2010. Depth choices and movements in relation to temperature were analysed from pressure and temperature records for 13 eels with implanted data storage tags, covering 17 overwintering periods and three intervening summer periods. Dormancy commenced in October–November as temperatures fell below 4–12 °C. Eels tended to remain motionless throughout the winter, with some short periods of activity signalled by small changes in depth distributions. During dormancy, the eel shows a clear avoidance of shallow areas <5 m in favour of the 10–25‐m‐depth interval. Activity tended to resume 4–6 months later in April–May as temperatures rose above 3–7 °C and ice cover broke, and eels spent more time at shallower depths of <5–10 m. The majority of the eels were assessed as being in the silver eel stage at the time of tagging. During the autumn months, the diving behaviour, with frequent and large vertical excursions and periods at the surface, was similar to that seen in migrating eels in the Baltic and Atlantic Ocean. In spring and summer, the behaviour differed, being dominated by more gradual depth variations, implying that the eels reverted from silver eel migration behaviour to yellow eel foraging behaviour. Body weight declined during dormancy, but other studies of starvation over comparable time periods showed significantly higher average specific weight losses, implying that the Mälaren silver eels must have fed between the end of dormancy and recapture.  相似文献   

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