Top PDF 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 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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Serum estradiol-17 beta and testosterone levels during silvering in wild Japanese eel Anguilla japonica.

Serum estradiol-17 beta and testosterone levels during silvering in wild Japanese eel Anguilla japonica.

Thorarensen, H., Young, G., Davie, P.S., 1996. 11-Ketotestos- terone stimulates growth of heart and red muscle in rainbow trout. Can. J. Zool. 74, 912–917. Tzeng, W.N., Han, Y.S., He, J.T., 2002. The sex ratios and growth strategies of wild and captive Japanese eels Anguilla japonica. In: Small, B., MacKinlay, D. (eds.), Developments in Understanding Fish Growth. International Congress on the Biology of Fish. University of British Columbia, Van- couver, Canada, pp. 25–42.
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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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Sex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan

Sex-dependent habitat use by the Japanese eel Anguilla japonica in Taiwan

In addition to the salinity-related habitat preference differences between sexes, the sex determination of young juvenile stage Japanese eels may also have been affected by salinity. The mean Sr:Ca ratios dif- fered significantly between sexes, not only beyond the elver stage, but also during the time period in which eel sex determination occurred. This indicated that the habitat use not only differed between the sexes but the habitat itself also might affect eel sex determination, e.g. high salinity habitats promote female sex differen- tiation and freshwater habitats promote male sex dif- ferentiation. The environmental sex determination has been demonstrated in many species (Docker & Bea- mish 1994) and evolves when an environmental factor is more advantageous to one sex than to the other, as is the salinity factor in the case of the eel. However, many other environmental factors that might affect anguillid eel sex determination are also reported. Individual eels experiencing rapid growth in the juvenile stage before sex differentiation tend to develop as males, whereas
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Identification and growth rates comparison of divergent migratory contingents of Japanese eel (Anguilla japonica)

Identification and growth rates comparison of divergent migratory contingents of Japanese eel (Anguilla japonica)

The rivers in both Japan and Taiwan were small, with limited freshwater, and thus most eels may be compelled to grow in the estuary. Although we did not examine the eels in the upper stream of the rivers in both Japan and Taiwan, the eels in the upper stream will be caught in the estuary during their downstream spawning migration. Accordingly, we believed that the ratios of life-history types of the silver eels collected in the estuary can represent those of the whole river system. The estuarine contingent contributed to approximately 60% of the eel population in both Japan and Taiwan. However, we do not know if the estuarine contingent is predominant in the eel population in the Pearl River System, because the fish caught in the estuary of the river were not examined.
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Use of otolith Sr:Ca ratios to study the riverine migratory behaviors of Japanese eel Anguilla japonica

Use of otolith Sr:Ca ratios to study the riverine migratory behaviors of Japanese eel Anguilla japonica

Although yellow American eels in brackish waters had faster growth rates than yellow eels from freshwater areas (Harrell & Loyacano 1982, Hansen & Eversole 1984, Helfman et al. 1984), the condition factor and growth curve of the Japanese eel in the Kaoping River did not differ significantly among migratory contin- gents. This indicated that the growth rate of the eel did not completely depend on the habitat. In addition to food availability and habitat carrying capacity, the genetics, physiology, homing behavior, temperature, population density, and intra- and inter-specific competition may potentially influence the migratory behavior of the eel. Further study is needed to better understand the migratory behavior of the eel in the river.
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Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr:Ca ratios

Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr:Ca ratios

Transcript levels of PRL mRNA in different develop- mental stages. Since the amount of total RNA of indi- vidual pituitaries, extracted using the total RNA purifi- cation kit, was not sufficient for northern blot analysis, RT-PCR and real-time quantitative PCR were thus cho- sen for PRL mRNA analysis. Total RNA (1 µg for each batch) from wild female pituitaries of yellow (n = 17, divided into 4 batches), pre-silver (n = 9, divided into 3 batches), and silver (n = 9, divided into 3 batches) Japanese eels, collected between 2000 and 2001, was reverse-transcribed as described. PCR was then per- formed at 50 µl final volume using an aliquot of the RT reaction and Primers 1 and 2. As a control in the RT- PCR reactions, β-actin was amplified simultaneously.
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Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr: Ca ratios.

Salinity preference of silvering Japanese eel Anguilla japonica: evidence from pituitary prolactin mRNA levels and otolith Sr: Ca ratios.

Transcript levels of PRL mRNA in different develop- mental stages. Since the amount of total RNA of indi- vidual pituitaries, extracted using the total RNA purifi- cation kit, was not sufficient for northern blot analysis, RT-PCR and real-time quantitative PCR were thus cho- sen for PRL mRNA analysis. Total RNA (1 µg for each batch) from wild female pituitaries of yellow (n = 17, divided into 4 batches), pre-silver (n = 9, divided into 3 batches), and silver (n = 9, divided into 3 batches) Japanese eels, collected between 2000 and 2001, was reverse-transcribed as described. PCR was then per- formed at 50 µl final volume using an aliquot of the RT reaction and Primers 1 and 2. As a control in the RT- PCR reactions, β-actin was amplified simultaneously.
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Synchronous changes of morphology and gonadal development of silvering Japanese eel Anguilla japonica.

Synchronous changes of morphology and gonadal development of silvering Japanese eel Anguilla japonica.

Abstract The gonadal development of Japanese eel Anguilla japonica during silvering was examined via gonadal histology and morphometric characteristics. Specimens were collected from the Kaoping River of Taiwan between November 1998 and November 2001. Female eels predominated, constituting 87.6% of the sex-determined eels. The degree of gonadal development was assessed by skin coloration, with female eels divided into yellow, pre-silver, and silver phases. Males were divided into yellow and silver phases because of small sample size. Silver phase eels predominated in the winter. Mean ( F S.E.) total length of silver-phase eels was significantly larger in females (642.2 F 10.4) than males (564.8 F 14.6) ( p < 0.001). The mean ( F S.E.) gonadosomatic index (GSI) of females increased significantly from 0.27 F 0.01 for yellow phase, to 0.55 F 0.03 for pre- silver and 1.32 F 0.07 for silver phase. Oocyte development progressed from the chromatin nucleolus stage in the yellow phase eel, through the peri-nucleolus stage in the pre-silver phase eel and to the oil-drop stage in the silver phase eel. Spermatogenesis was active for silver phase males which had a larger mean GSI (0.15 F 0.01) than yellow phase males (0.07 F 0.02), but the gonadal development of males was slower than that of females. GSI, ocular index (OI), and fin-index (FI) were positively correlated, and gut-index (GI) was negatively correlated with total length in both sexes. Residual analysis of the regression of the indices GSI, OI, FI, and GI on TL indicated that the variation of the indices with growth was greatly influenced by the developmental phase of the eel.
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Use of the Sex Ratio as a Means of Resource Assessment for the Japanese Eel Anguilla japonica: A Case Study in the Kaoping River, Taiwan

Use of the Sex Ratio as a Means of Resource Assessment for the Japanese Eel Anguilla japonica: A Case Study in the Kaoping River, Taiwan

A negative relationship between the proportion of females and the population density was found when compil- ing historical data of both wild and cultured Japanese, European, and American eels. Based on the relation- ship, the population status of the Japanese eel Anguilla japonica was assessed. Japanese eel samples were collected from the lower reaches of the Kaoping River in southwestern Taiwan from 1998 to 2002, and the pop- ulation density was estimated by mark-recapture experiments in 2001 and 2002. The sex ratio of the eel was skewed towards females, accounting for 81.3%-88.3% in the total samples of yellow and silver eels and for 63.6%-81% in the silver stage eels. The significant female-skewness of the sex ratio validated that the popula- tion of Japanese eels in the Kaoping River has declined to a very low level in recent years. The population density of the Japanese eel in the lower reaches of the Kaoping River was approximately 0.01 eels/m 2 in 2001 and 2002. The decline in the Japanese eel population in the Kaoping River has probably resulted from both overfishing of glass eels in the estuary for aquaculture needs which severely influences recruitment, and degra- dation of the growth habitat of the yellow eel along the river. The sex ratio therefore is a fast and reliable indi- cator for eel resource assessment. http://zoolstud.sinica.edu.tw/Journals/45.2/255.pdf
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Modelling the growth of Japanese eel Anguilla japonica in the lower reach of the Kao-Ping River, southern Taiwan: an information theory approach

Modelling the growth of Japanese eel Anguilla japonica in the lower reach of the Kao-Ping River, southern Taiwan: an information theory approach

The von Bertalanffy growth model with sex-specific parameters was best supported by the data from published literature, but there is substantial support for the Gompertz, generalized von Bertalanffy and power growth models. Because the von Bertalanffy growth models of both sexes nearly overlapped the averaged growth model, which resulted in only a minor improvement in MSE (0.16 %), the von Bertalanffy growth model with sex-specific coefficients might describe the growth of A. japonica as well as the averaged growth models for age 1–8 years. The females attained larger L T at age than the males and the differences became large at older ages, which might be related to the differences in life history strategies between sexes.
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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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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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Salinities, not diets, affect strontium/calcium ratios in otoliths of Anguilla japonica

Salinities, not diets, affect strontium/calcium ratios in otoliths of Anguilla japonica

b Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan, ROC Received 29 July 2006; received in revised form 23 October 2006; accepted 23 October 2006 Abstract Although otolith Strontium (Sr)/calcium (Ca) ratios have been widely used to reconstruct the past salinity environmental history of anguillid eels, factors affecting the Sr/Ca ratios in otoliths are incompletely understood. Japanese Eel (Anguilla japonica) elvers (mean length 54.7 ± 2.1 mm) were collected in the estuary during their upstream migration and reared at 5 different salinities (0, 5, 15, 25, and 35 psu) and 3 types of feeding conditions (formulated feed, tubifex, and starvation) for 30 days to evaluate the effects of salinity and diets on otolith Sr/Ca ratios. Ca and Sr concentrations in the ambient water significantly increased with salinity (SAL) as [Ca] water = 15.50SAL−5.56, and [Sr] water = 0.21SAL + 0.03, respectively. Sr/Ca ratios in otoliths increased with salinity (SAL) of the rearing water as [(Sr/Ca) × 1000] otolith = 0.091SAL + 3.790. In diets, Sr/Ca ratios were 4 times higher in tubifex than in formulated feed. However, in otoliths, ANOVA indicated that Sr/Ca ratios did not differ significantly between groups fed on tubifex or formulated feed (p = 0.118). Otolith Sr/Ca ratios were negatively correlated with fish growth rates while the growth rates differed significantly among rearing conditions with different salinities and diets. Partition coefficients of the Sr/Ca ratios from ambient water to fish tissues and otoliths significantly increased with salinity. The Sr/Ca ratios of Japanese Eel otoliths thus were positively correlated with the ambient salinity and decreased with increasing fish growth rate, but was not affected by fish diet.
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Effects of salinity and ontogenetic movements on strontium:calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel

Effects of salinity and ontogenetic movements on strontium:calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel

The relationship between Sr/Ca ratios in the otoliths of reared eels and ambient salinity (Fig. These data also validate the use of Sr/Ca ratios in otoliths as [r]

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Effects of salinity and ontogenetic movements on strontium: calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel.

Effects of salinity and ontogenetic movements on strontium: calcium ratios in the otoliths of the Japanese eel, Anguilla japonica Temminck and Schlegel.

The relationship between Sr/Ca ratios in the otoliths of reared eels and ambient salinity (Fig. These data also validate the use of Sr/Ca ratios in otoliths as [r]

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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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The silvering of the Japanese eel Anguilla japonica: season, age, size and fat

The silvering of the Japanese eel Anguilla japonica: season, age, size and fat

2 Taiwan Fisheries Research Institute, 199 Hou-Ih Road, Keelung, Taiwan Abstract This study aims to understand the changes in age, total length, body weight, and muscle fat content in the Japanese eel Anguilla japonica during silvering, from yellow to silver eels, and their physiological significances. Eels were collected from the downstream of the Kaoping River of southern Taiwan from November 1998 through November 1999. The female eels were classified into three developmental stages based on external skin coloration and oocyte diameter, namely yellow, pre-silver and silver eel stages. The male eels were classified into yellow and silver eel stages only.
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Timing of metamorphosis and estuarine arrival across the dispersal range of the Japanese eel Anguilla japonica.

Timing of metamorphosis and estuarine arrival across the dispersal range of the Japanese eel Anguilla japonica.

The mean increment widths of the otoliths from the outer core to the metamorphosis check for the elvers collected at the 6 estuaries showed a geographic cline that dec[r]

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