Top PDF The swimbladder parasite Anguillicola crassus in native Japanese eels and exotic American eels in Taiwan

The swimbladder parasite Anguillicola crassus in native Japanese eels and exotic American eels in Taiwan

The swimbladder parasite Anguillicola crassus in native Japanese eels and exotic American eels in Taiwan

(Accepted April 30, 2008) Yu-San Han, Ya-Ting Chang, Horst Taraschewski, Su-Ling Chang, Che-Chun Chen, and Wann-Nian Tzeng (2008) The swimbladder parasite Anguillicola crassus in native Japanese eels and exotic American eels in Taiwan. Zoological Studies 47(6): 667-675. To understand differences in infection patterns of the swimbladder parasite Anguillicola crassus between habitats and eel species in Taiwan, the prevalence and intensity of the parasite were examined based on specimens collected from wild and cultured Japanese eel Anguilla japonica and from exotic cultured American eel A. rostrata in the Kaoping River and culture ponds in southwestern Taiwan in 2006-2007. The prevalence of Aco. crassus in wild Japanese eels was lower in winter compared with summer/autumn, varying 33%-58%, with a mean intensity of 1.5-4.4. The prevalence and intensity were size- dependent and increased with eel size. In cultured Japanese eels, the prevalence and mean intensity varied greatly at 3%-68% and 1.0-29.0, respectively. In cultured American eels, the prevalence and intensity were very high in ponds without drug treatment. In contrast to wild eels, the mean intensity of larval and adult worms showed a size-dependent decreasing trend in cultured eels. The mean body mass of Aco. crassus in American eels was significantly larger than that in Japanese eels. The external morphology, condition factor, and hepatosomatic index showed no significant differences between infected and uninfected groups, indicating a low pathogenic effect of Aco. crassus on these 2 eel hosts. Our results showed that both native Japanese eels and naive American eels are highly susceptible to Aco. crassus, but it causes little pathogenicity under good pond management. http://zoolstud.sinica.edu.tw/Journals/47.6/667.pdf
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Occurrence of Anguillicola crassus (Nematoda: Dracunculoidea) in Japanese eels Anguilla japonica from a river and an aquaculture unit in SW Taiwan

Occurrence of Anguillicola crassus (Nematoda: Dracunculoidea) in Japanese eels Anguilla japonica from a river and an aquaculture unit in SW Taiwan

Similar intensity values (1.3 to 2.8) were recorded for the larvae. In cultured eels, prevalence as well as mean intensities were higher. In the cultured hosts, mean larval intensities exceeded those of adult worms 2-fold, and maximum larval intensities were 4- to 5-fold higher than in eels from the river. In cultured eels, dead larvae were also more abundant than in wild eels. We conclude that infrapopula- tions of A. crassus in Japanese eels are regulated by the defense system of this host, intraspecific den- sity-dependent regulation being less likely as the major regulatory mechanism. No influence of the parasite on eel condition was found in either wild or cultured eels, indicating a low or moderate path- ogenic effect of A. crassus on this host. This study shows that A. crassus is moderately common in cul- tured and wild Japanese eels in Taiwan, where the parasite is endemic.
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The exotic American eel in Taiwan: ecological implications

The exotic American eel in Taiwan: ecological implications

Tabeta, 1983). The Japanese eel A. japonica is a commercially important species for aquaculture in Taiwan. As the catch of Japanese eel elvers has been deemed insufficient to meet the demand of eel aquaculture (Tzeng, 1996), elvers of exotic eel species, mainly American eel and European eel, have been imported since 1969 and 1977, respectively (Li, 1997). In Japan, European eels have been found in the Shinjiko Lake and Mikawa Bay (Zhang et al., 1999), and are abundant in the Uono River (Aoyama et al., 2000). To date, no exotic eels have been documented in the natural waters of Taiwan. The external morphologies of native and introduced eels are quite similar, complicating the identifi- cation of exotics. In this study, exotic eel species were identified by phylogenetic analysis of the mitochondrial cytochrome b gene (mtCyt-b). In addition, the age, growth and maturity of exotic eels were examined to evaluate the condition of introduced eels in the natural environment of Taiwan.
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The exotic American eel in Taiwan: ecological implications.

The exotic American eel in Taiwan: ecological implications.

Tabeta, 1983). The Japanese eel A. japonica is a commercially important species for aquaculture in Taiwan. As the catch of Japanese eel elvers has been deemed insufficient to meet the demand of eel aquaculture (Tzeng, 1996), elvers of exotic eel species, mainly American eel and European eel, have been imported since 1969 and 1977, respectively (Li, 1997). In Japan, European eels have been found in the Shinjiko Lake and Mikawa Bay (Zhang et al., 1999), and are abundant in the Uono River (Aoyama et al., 2000). To date, no exotic eels have been documented in the natural waters of Taiwan. The external morphologies of native and introduced eels are quite similar, complicating the identifi- cation of exotics. In this study, exotic eel species were identified by phylogenetic analysis of the mitochondrial cytochrome b gene (mtCyt-b). In addition, the age, growth and maturity of exotic eels were examined to evaluate the condition of introduced eels in the natural environment of Taiwan.
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Growth and habitat residence history of migrating silver American eels transplanted to Taiwan.

Growth and habitat residence history of migrating silver American eels transplanted to Taiwan.

This study compares growth performance and migratory behavior, using otolith stron- tium (Sr)/calcium (Ca) ratios of those six American eels with cohabitating Japanese eels and American eels in North America. Regardless of sex, mean age at maturity of the exotic American eels was greater and mean annual growth rate was less than that of Japanese eels in Taiwan and similar to that of American eels in the southern United States. Sr/Ca ratios at the otolith edge of the six exotic American eels, which recorded their salinity history, increased significantly. Furthermore, four of the six exotic Ameri- can eels spent more than one year in the high-salinity estuary. Their extended residence in the estuary may be due to a delayed spawning migration resulting from a failure to orientate and migrate properly to their native spawning site.
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Facultative catadromy in American eels: Testing the conditional strategy hypothesis

Facultative catadromy in American eels: Testing the conditional strategy hypothesis

3 Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei, Taiwan 106, ROC 4 Institute of Earth Sciences, Academia Sinica, PO Box 1-55, Nankang, Taipei, Taiwan 115, ROC 5 Institute of Oceanography, College of Science, National Taiwan University, Taipei, Taiwan 106, ROC ABSTRACT: Analyses of otolith strontium:calcium (Sr:Ca) ratios in 162 American eels Anguilla ros- trata of the St. Jean River watershed in eastern Canada demonstrated the co-existence of 6 migratory patterns, including freshwater and brackish water residence, and the predominance of an amphidro- mous migratory behavior. We tested the hypothesis that the choice of a particular life-history tactic may be controlled by a conditional strategy with status-dependent selection. This prediction was not supported because migratory patterns did not vary as a function of individual size, age and/or sex of eels prior to migration. However, we demonstrated that the utilisation of the estuarine brackish envi- ronment, more productive than the freshwater river and lake, resulted in a higher growth rate. Fresh- water yellow eels, the typical catadromous tactic, were rare and experienced lower growth rates.
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Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China

Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China

(Sun Yet-Sen) University, Guangzhou 510275, PROC (Received 13 January 2000, Accepted 21 June 2000) The Sr/Ca ratios in otoliths of silver Japanese eels Anguilla japonica in Pearl River, China, indicated that both sexes did not stay in brackish water and grew in fresh water from the glass eel stage until spawning migration. This did not support the hypothesis that females tended to distribute upstream and males might be restricted to estuaries. The back-calculated total length of males at glass eel stage was not significantly different from that of females, indicating that the hypothesis that small glass eels became males and larger ones became females may not be true.
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The sex-ratio reversal of the Japanese eel Anguilla japonica in the Kaoping River of Taiwan: The effect of cultured eels and its implication

The sex-ratio reversal of the Japanese eel Anguilla japonica in the Kaoping River of Taiwan: The effect of cultured eels and its implication

The sex ratio of wild Japanese eels in the Kaoping River of southwestern Taiwan has been extremely skewed towards females in the recent years. However, the sex ratio skewed towards males after Typhoon Mindulle, July 2, 2004 then recovered to the previous female-dominated status in the following year. To determine why the sex ratio drastically changed, eels captured in the river were examined by both morphologic characteristics and otolith elemental signatures by solution-based inductively coupled plasma mass spectrometry (SB-ICPMS) and laser-ablation ICPMS (LA-ICPMS). Most of the eels collected in the river after the typhoon had a blue-gray colored back, with morphology and sex ratio similar to that of cultured eels, which differed from wild yellow eels which had a green colored back. The chemical signature in otoliths of eels with a blue-gray colored back was similar to that of cultured eels, with significantly lower Sr/Ca ratios but slightly higher Mn/Ca ratios than for wild eels. This confirmed that the reversal in eel sex ratio in the Kaoping River estuary resulted from cultured eels that had escaped from eel farms. Eel farmers estimated that about 30,000 eels escaped during the typhoon, sufficient to reverse the sex ratio of the eels in the river. Furthermore, silver eels caught in the estuary in the winter 2004 were also mostly males. The chemical signature in otoliths of these silver eels was similar to that of escaped cultured eels. Their morphology and mean GSIs, however, were comparable to wild silver eels. Thus, cultured eels that have escaped from eel farms can silver normally in the wild. Consequently, cultured eels may help to balance the sex ratio of the wild eel population and may contribute to the spawning stock of Japanese eel.
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Variation in the annual growth, by sex and migration history, of silver American eels Anguilla rostrata

Variation in the annual growth, by sex and migration history, of silver American eels Anguilla rostrata

2 Institute of Zoology, and 3 Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan 11529, ROC 4 Institute of Fisheries Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan 10617, ROC ABSTRACT: Silver American eels Anguilla rostrata from the East River, Chester, on the Atlantic coast of Nova Scotia, as evaluated by the temporal pattern of Sr:Ca ratios in their otoliths, showed variable patterns of migration between river and estuarine/marine waters during their yellow eel stage. Eels with a history of primarily estuarine residence were longer (total length) at migration and had higher annual growth rates than did eels with a primarily freshwater residence. Female eels were longer at migration and had higher annual growth rates than did males. The percentage (64%) of silver eels with a history of estuarine residence and their larger size at age, size at migration, and higher growth rate relative to freshwater resident eels may result from higher productivity in oceanic than fresh- waters at higher latitudes, as modified by regional environmental conditions. Environmental condi- tions change with increasing latitude in a different pattern for American and Japanese eels than for European eels.
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Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China.

Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China.

(Sun Yet-Sen) University, Guangzhou 510275, PROC (Received 13 January 2000, Accepted 21 June 2000) The Sr/Ca ratios in otoliths of silver Japanese eels Anguilla japonica in Pearl River, China, indicated that both sexes did not stay in brackish water and grew in fresh water from the glass eel stage until spawning migration. This did not support the hypothesis that females tended to distribute upstream and males might be restricted to estuaries. The back-calculated total length of males at glass eel stage was not significantly different from that of females, indicating that the hypothesis that small glass eels became males and larger ones became females may not be true.
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The sex ratios and growth strategies of wild and captive Japanese eels Anguilla japonica

The sex ratios and growth strategies of wild and captive Japanese eels Anguilla japonica

The role of gender and sexual differences in the growth histories of Japanese eel Anguilla japonica were linked with respect to the sex ratio and growth rate of wild eels collected from Taiwanese rivers. The sex ratio of wild eels was compared with that of eels semi-intensively cultured in a pond and intensively cultured in an aquarium. The sex ratio of wild eels from a low-density river habitat was dominated by females (86.4% of sex-determined eels), slightly dominated by males (57.1%) in a cultured pond, and dominated by males (90.0%) in an aquarium. This evidence supported the hypothesis that the sex of eels is determined by population density. The parameters of the von Bertalanffy growth equation demonstrated that males grew faster to reach a smaller asymptotic length than did females. We propose that the variation in eel sex ratio interacts with sex-linked differences in growth strategy to play an important role in density-dependent population regulation.
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Prevalence and intensity of occurrence of vaterite inclusions in aragonite otoliths of American eels Anguilla rostrata

Prevalence and intensity of occurrence of vaterite inclusions in aragonite otoliths of American eels Anguilla rostrata

Analyses of anguillid otolith Sr:Ca ratio transects have commonly been used to evaluate their residence and mi- gratory history between habitats of different salinity (Daverat et al. 2006, Jessop et al. 2008). Replicate, closely spaced Sr:Ca ratio transects produced close estimates of the proportion of freshwater residence for eels of largely estuarine residence, as required for the method to be useful. Although suitable transect paths for microchem- ical analysis may be found in highly vateritic otoliths, some otoliths may be entirely composed of vaterite and unsuitable for use. When an Sr:Ca ratio transect crossed vaterite inclusions, the proportion of freshwater resi- dence was greatly overestimated. Fortunately, the pres- ence of vaterite inclusions in otoliths is readily deter- mined and their intensity in American eel otoliths is typically small, reducing the potential bias in estimating habitat residence period; but if overlooked, the fre- quency of inter-habitat migration can be overestimated.
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Life history of american eels from Western Newfoundland

Life history of american eels from Western Newfoundland

to their positive relation with TL, but comparison with eels of similar size show index differences that are sufficiently large to be real. A progressive increase also occurs in maturation indices (GSI, EI, and PFI) during migration, with consequent effect on the comparison of maturation indices among sites due to the timing of sampling. Minor differences in index values, particu- larly GSI, may result from different methods of estimation among studies. A lower degree of sexual maturation at the onset of the spawning migration in more northerly eel stocks and the additional develop- mental period available during their longer marine migration may permit fish from different latitudes to reach the spawning ground at approximately similar times and reproductive condition (Wenner 1973;
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Migratory behaviour and habitat use by American eels Anguilla rostrata as revealed by otolith microchemistry

Migratory behaviour and habitat use by American eels Anguilla rostrata as revealed by otolith microchemistry

The hypothesis that the high Sr:Ca ratios at the edge of some silver eel otoliths is an artefact of otolith prepa- ration and analysis rather than a reflection of the most recent environmental history of the eel is perhaps the most plausible. The transect of Sr:Ca ratios along the otolith radius may not always reach the exact edge of the otolith, the radius analysed may not be the longest one, with consequent compression of the temporal pat- tern of otolith composition at the edge, and the pol- ished plane of the otolith may be slightly rounded at the edge. If the final Sr:Ca ratio is not exactly at the otolith edge, the evidence of recent habitat change may be absent. Given that otolith growth is much reduced at older ages, the time to incorporate Sr and Ca may be increased and slower growth may magnify Sr levels (Kalish 1989). If it takes about a month to incorporate evidence of habitat change in the otoliths of fast growing juvenile eels, it may take much longer in slow growing silver eels. If Sr persists in the blood- stream for a while after a move from estuary to river, Sr:Ca ratios intermediate between those in freshwater and estuary may arise (Howland et al. 2001). The sharp decline in otolith Sr:Ca ratio spot values near the otolith edge in most silver eels with mean ratios between 4.50 × 10 – 3 and 4.99 × 10 – 3 supports the inter- pretation of a lag in the manifestation of habitat change within the otolith. The time period represented in the otolith chronology by a microprobe spot of a given size also tends to increase as the otolith edge is approached, blurring the determination of the time at which a habitat shift occurred. Consequently, the final
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Effects of inter-habitat migration on the evaluation of growth rate and habitat residence of American eels Anguilla rostrata

Effects of inter-habitat migration on the evaluation of growth rate and habitat residence of American eels Anguilla rostrata

fwg) groups, respectively, to their next higher groups when based on residence time. Thus, otolith growth proportion was again found to be basically equivalent to habitat residency proportion. However, where the growth rate differences between habitats are much higher than those observed here, such as for American eels from Prince Edward Island (Lamson 2005), biolog- ically and analytically important differences may occur between otolith growth proportion and habitat resi- dency period. The close match of the habitat residence model with the observed data suggests that the model may be usefully applied to predict the relationship between otolith growth and habitat residence period for yellow and silver eels, with mean growth rates sim- ilar to those observed in this study, but it requires fur- ther verification for higher mean growth rates.
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A Polymerase Chain Reaction for Detecting Herpesvirus anguillae in Asymptomatic Eels

A Polymerase Chain Reaction for Detecting Herpesvirus anguillae in Asymptomatic Eels

With this primer set, a 622-bp fragment is expected to be amplified from HVA genomic DNA. The deproteinized DNA samples were used for amplification in a 10 µL reaction mixture containing 10 mM Tris-HCl, pH 8.3, 50 mM KCl, 2 mM MgCl 2 , 200 µM each of dNTP, 1 µmol each of primers, 4 units of Taq DNA polymerase (Biotools, USA). The amplification was performed in a RapidCycler Thermal programmer (Idaho Technology, USA) using 10-µL glass capillaries. Twenty five amplification cycles were run, each cycle consisting of a denaturation step at 94℃ for 0 s, annealing at 55℃ for 0 s, extension at 72℃ for 25 s. Since the temperature of a totally 10 µL reaction mixture was easily equilibrium inside a glass capillary as it reached the setting point during PCR, the period of both denaturation and annealing steps were not necessarily prolonged. Thus a very rapid reaction processing for only half hour was achieved.
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Otolith Sr:Ca Ratios as Natural Mark to Discriminate the Restocked and Naturally Recruited European Eels in Latvia

Otolith Sr:Ca Ratios as Natural Mark to Discriminate the Restocked and Naturally Recruited European Eels in Latvia

The average otolith Sr:Ca ratios of last three measuring points were able to represent the salinity of sampling site. The otolith annulus pattern was similar between Nat and Rst eels except more annuli found in the otoliths of Rst eels. The age at first freshwater entry of the eels was similar between eels from Lat- vian and Lithuanian waters, indicating the migration across the Baltic Sea was spatially and temporally persistent during investigated period. The growth of FW (Rst) eels was not consistently slower than the IHS (Nat) eels in the sampling sites, indicating a complicated site–origin interaction on the growth of the eel. This study further suggested the impor- tance of otolith Sr:Ca ratio as natural mark to discriminate the restocked European eels from naturally-recruited eels in the Baltic countries. The eels in the Baltic regions were still less studied and future research efforts were still needed.
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A Study of Intercultural Effectiveness for American and Japanese Expatriates in Taiwan 吳永欽、韓必霽

A Study of Intercultural Effectiveness for American and Japanese Expatriates in Taiwan 吳永欽、韓必霽

The purpose of the research was to investigate Intercultural Effectiveness Competencies (ICE) for American and Japanese Expatriates in Taiwan. The ICE were success or competence in cross-cultures. Han (1997) concluded ICE were: 1.Communication competence 2.Psychological stress 3.Relationship building 4.Cultural empathy 5.Cross-cultural awareness. The research quoted 5 ICE items from Han and revised in English and Japanese questionnaires. The target population were American and Japanese expatriates in Taiwan. The data were analyzed with the SPSS software package and were submitted to MANOVA procedures corresponding to each hypothesis. Conclusion: 1.for all: ICE of respondents located in the category of American expatriates reported higher means than those respondents located in the category of Japanese expatriates. 2.for American expatriates:The following people have higher ICE: The higher stratum in the organization; working more than three years in other countries; willing to work in multinational enterprises in their career planning; having international co-workers. 3.for Japanese expatriates: The following people have higher ICE: local languages ability; international experience; having experience with other cultures; having participated in cross-cultural training programs; having international co-workers.
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Time Series Analysis of Taiwanese Catch Data of Japanese Glass Eels Anguilla japonica: Possible Effects of the Reproductive Cycle and El Niño Events

Time Series Analysis of Taiwanese Catch Data of Japanese Glass Eels Anguilla japonica: Possible Effects of the Reproductive Cycle and El Niño Events

The movement of a salinity front in the spawning ground, which is associated with the ENSO, may control the success of larval transport from the NEC to East Asia, thereby affecting glass eel recruitment success (Kimura et al. 2001, Kim et al. 2007). In addition, the number of Japanese eel larvae transported to the Kuroshio Current was much smaller than that to the Mindanao Current in an El Niño year, and recruitment decreased in those years in Japan. In non-El Niño years, the number transported to the Kuroshio Current was twice as high, and recruitment increased (Kim et al. 2007). In this study, average numbers of the glass eel catch in El Niño years in Taiwan were lower but did not significantly differ from those in normal or La Niña years. This implies that ENSO events might not play a major role in shaping glass eel recruitment in Taiwan. However, during stronger El Niño years, the mean glass eel catch was significantly lower than the mean glass eel catch during La Niña years. This indicates that stronger El Niño events seem to be able to modify the recruitment pattern of glass eels in Taiwan to some extent. The different effects of oceanic currents on glass eel recruitment between Taiwan and Japan might be due to different effects at both ends of the Kuroshio Current, as Taiwan is located near the start site of the Kuroshio Current while Japan is at its terminal end. The analysis of interactions between biotic and abiotic factors on shaping the pattern of glass eel recruitment would greatly benefit if glass eel catch data from other regions could be obtained.
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Decreased Sr/Ca ratios in the otoliths of two marine eels, Gymnothorax reticularis and Muraenesox cinereus, during metamorphosis.

Decreased Sr/Ca ratios in the otoliths of two marine eels, Gymnothorax reticularis and Muraenesox cinereus, during metamorphosis.

to stay closer to the continental shelf grounds. This implies the adoption of different migration and meta- morphosis strategies. The mean otolith daily growth increment width and its variability in moray eels during early development are more apparent than for pike eels, indicating that the growth rates of moray eels may be higher and more variable. Moreover, moray eels may inhabit a more variable shallow-water marine environment that is nutrient-rich but fluctuates greatly in environmental conditions such as water temperature due to the influ- ence of a nearby continent. Thus moray eels may have evolved to a shorter larval duration, and higher and varied larval growth in order to pass from a pelagic to a benthic habitat as soon as possible.
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