Top PDF 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.

Abstract In a previous study, we had observed synchronous changes of morphology and gonadal development in wild Japanese eel during the silvering process. In this study, we aimed to clarify if gonadotropin is the key hormone responsible for this phenomenon. Yellow eels captured in the Kaoping River were repeatedly injected with human chorionic gonadotropin (HCG), and changes of morphology and gonadal development were examined. After five weekly injection of HCG at a dosage of 0.75 IU/g body weight, eels was classified into well-responsive and poor-responsive groups according to skin coloration. Approximately 50 % of males and 20 % of females were responsive to become silver eels. Mean age, total length, body weight, condition factor, gonadosomatic index (GSI), fin-index (FI), hepatosomatic index (HSI) and ocular index (OI) were significantly higher in well-responsive eels than in poor-responsive eels. The mean digestosomatic index (DSI), in contrast, significantly decreased in well-responsive eels compared to poor ones. OI was positively correlated and DSI was negatively correlated with the GSI in both sexes. These results indicated that well developed eels are more sensitive to HCG treatment, and the skin color, eye size, gonadal development and digestive tract shrinkage were synchronous after HCG injection. The pituitary – gonad axis plays important role on eel silvering.

gonadal development thus depends totally on large amount of fat accumulating in the body. From this point of view, it is reasonable to suppose that the migration in silver phase may need a minimum level of fat reserves (36) . The hypothesis is also supported by our study in Japanese eels. The fat stores in muscle range between 13-25% (mean 18%) in the silver stage (Table 1), and the lowest limit of silvering is 13% in both sexes. However, Svedäng and Wickström (37) found that the silver European eels of few sampling areas have mean muscle fat content lower than 10%, some specimens have fat stores even as low as 1%. They suggest that the maturation process in eel may be more flexible than were thought before, and migration together with gonad development might arrest temporarily and resume feeding to accumulate enough fat reserves before migration starting again. Since the eel stage was judged only by visual inspection in their study without gonadal histology and data of morphometric index, error judgment of stages might occur and result in the underestimation of fat content in silver eels.

Yung-Song Wang and Show-Wan Lou* (Received, May 1, 2007; Accepted, June 15, 2007) ABSTRACT This study examines Japanese eel ovary responded to the administration of exogenous sexual hormone throughout the reproductive process. In short-term experiment, ovarian follicle exhibited sensitivity to salmon pituitary homogenate (SPH) and sexual steroids (E 2 and MT) in the early vitellogenic stages. The apoptotic signals were exclusively localized in the outer theca layer which was detected from in situ TUNEL, furthermore, the appearance of the apoptotic signal in the early vitellogenic stage seems to correlate with a reduction of oocyte numbers in long-term experiment. In long-term experiment, the mean GSI and total oocyte numbers indicated that multiple injections of E 2 or MT were not of much benefit to promote the gonadal development of those fish. Despite SPH treatment was an effective and indispensable method to hasten artificially sexual maturation, and the size-frequency distribution indicated that the most developed oocytes of those were growing from the vitellogenic stage to the final maturational phase. However, the treatment of SPH plus E 2 failed to promote the ovarian development and exhibited a remarkable reduction of total oocyte numbers. Of interest is the synergistic effect of SPH plus MT revealed that MT, a potent, aromatizable androgen, provides a potential usefulness to participate the process of vitellogenesis when it combines with SPH treatments, furthermore, the synergistic effect actually enhances the survival and synchronous development of ovarian follicle throughout the reproductive process.

development of the gonad. Accordingly, the HPT axis may be involved in eel silvering. However, no information is yet available with respect to the corresponding changes in thyroid status during silvering of Japanese eels. We therefore investigated the changes in the pituitary–thyroid axis during silvering of wild Japanese eels. As a direct assay of eel TSH is unavailable as yet, the TSH
transcript levels were estimated to represent thyrotropin expression activity from the pituitary. The circulat- ing thyroxine levels were estimated to reflect the thyroid status. Since the genome and peptide sequence of TSH
for Japanese eel are not known yet, we also cloned the TSH
gene for phylogenetic analysis. We report here the cloning of the genomic and cDNA sequences for Japanese eel TSH
and its deduced peptide sequence, the regulation of TSH
mRNA expression, and the changes in TSH
mRNA expression levels together with circulating thyroxine levels at various stages of ovarian development during silvering of wild female Japanese eels.

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.

d Received 19 June 2003; received in revised form 5 September 2003; accepted 6 September 2003 Abstract To understand the changes of serum levels of sex steroids in the wild Japanese eel Anguilla japonica during silvering process, eels collected from the Kaoping River of Taiwan from August 2000 through June 2001 were examined. The maturational stages of female eels before and during silvering were divided into four stages: juvenile, sub-adult, pre- silver and silver stages based on skin coloration and oocyte diameter. Male eels were investigated only in the silver stage. Radioimmunoassays were employed to measure serum levels of estradiol-17b (E ) and testosterone (T). The 2

ABSTRACT: The salinity preference of Japanese eel Anguilla japonica during silvering was vali- dated from the viewpoints of physiological ecology by examining the pituitary prolactin (PRL) mRNA expression and the otolith strontium:calcium (Sr:Ca) ratios of the eels of different sexual maturity stages collected in an estuary of Taiwan. The PRL possessed a putative signal peptide of 24 amino acids and a mature peptide of 185 amino acids. RT-PCR and real-time quantitative PCR analyses indi- cated that the transcript levels of PRL mRNA significantly decreased from yellow to silver stage. On the contrary, the Sr:Ca ratios at the otolith edge of silver eels, which recorded their latest experience of salinity history, significantly increased. The increase in otolith Sr:Ca ratios and the decrease in PRL mRNA expression are consistent with the timing of migration from freshwater to seawater during silvering of the eel.

ABSTRACT: The salinity preference of Japanese eel Anguilla japonica during silvering was vali- dated from the viewpoints of physiological ecology by examining the pituitary prolactin (PRL) mRNA expression and the otolith strontium:calcium (Sr:Ca) ratios of the eels of different sexual maturity stages collected in an estuary of Taiwan. The PRL possessed a putative signal peptide of 24 amino acids and a mature peptide of 185 amino acids. RT-PCR and real-time quantitative PCR analyses indi- cated that the transcript levels of PRL mRNA significantly decreased from yellow to silver stage. On the contrary, the Sr:Ca ratios at the otolith edge of silver eels, which recorded their latest experience of salinity history, significantly increased. The increase in otolith Sr:Ca ratios and the decrease in PRL mRNA expression are consistent with the timing of migration from freshwater to seawater during silvering of the eel.

Advantages include such aspects as increased food supply, avoidance of potentially harmful environmental conditions and/or a movement to more favorable ones, the occupation of habitats that have specific or specialized habitat requirement, and the availability of more living space. Costs of migration include mortalities resulting from migration itself, changed environmental conditions that may be intolerable (in diadromous fishes, specifically osmoregulatory stress) (McDowll, 1988). Gross (1987) proposed that diadromy occurs when the gain in fitness from using a second habitat minus the migration costs of moving between habitats exceeds the fitness from staying in only one habitat. When the elvers migrate from offshore seawater to upstream freshwater for living habitat and feeding, they have to overcome the osmotic pressure of salinity gradient environment. If they stayed in estuary their osmoregulatory cost would be lower than those in both freshwater and sea water. Meanwhile, the stability of water volume, living space and food abundance for the eel is generally superior in the estuary than the upper stream of the river in the island countries, such as Japan and Taiwan. The estuary functions as a nursery and feeding ground for the juveniles of many inshore fish and offers commercially important fish (Wallace et al., 1984;

Ming-Iu Lai, Student Member, IEEE, Tzung-Yu Wu, Jung-Chin Hsieh, Chun-Hsiung Wang, and Shyh-Kang Jeng, Senior Member, IEEE Abstract—In this paper a compact switched-beam antenna is proposed. The antenna is composed of a four-element antenna array based on L-shaped quarter-wavelength slot antenna ele- ments. Such an antenna element is a planar structure and presents a directional radiation pattern in the azimuth plane. Its maximum radiation direction is toward near the direction of the open end of the slot. As a result, the open ends of the four slot antennas are arranged toward 0 2 , and 3 2, respectively. The statuses of these antennas are controlled by some diodes. Con- sequently, by carefully controlling the diodes, an antenna with several switchable patterns can be achieved. To prove the concept, a 2.4–2.5 GHz switched-beam antenna for WLAN applications is designed and implemented. Its size is 52 mm in square. The antenna possesses eight directional patterns and many nearly omnidirectional patterns in the azimuth plane. The experiment results fully demonstrate the performance of the proposed design.

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]

Type 3 measurements differed from Types 1 and 2 in not having consistent low or high Sr:Ca ratios. Fig. 3d –i illustrate the diversi- fied temporal changes of Sr:Ca ratios in the otoliths of Type 3 eels. For example, Case 1: the Sr:Ca ratio be- yond the elver check gradually decreased from 7 × 10 – 3 at the elver check to less than 4 × 10 – 3 at the otolith edge (Fig. 3d,e), indicating that the eel after the elver stage gradually migrated to freshwater. Case 2: the Sr:Ca ratios decreased gradually after the elver check to a low level less than 4 × 10 – 3 at ages-1 and -2, and then increased to reach a peak approximately 8.0 × 10 – 3 at age-3. After age-3, it decreased to less than 4 × 10 – 3 again (Fig. 3f). This indicated that the eel migrated into freshwater at ages-1 and -2, rather than migrating out the river into the seawater at age-3 and re-invading the river again. Case 3: the Sr:Ca ratios after the elver check decreased to less than 4 × 10 – 3 from 1 to 4 yr old, then increased to greater than 5 × 10 – 3 thereafter (Fig. 3g,h,i). This indicated that these eels had migrated to freshwater during young yellow eel stage, rather than migrating into seawater, and did not re-entry the river until collected. These phenomena indicated a di- versified habitat use and flexible migratory behavior in the yellow phase. Type 3 eels were further divided into

Yu-San Han 1, 2, *, Chia-Ling Hung 2 , Yi-Fen Liao 2 , Wann-Nian Tzeng 1, 2 1 Department of Life Science and 2 Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei 106, Taiwan ABSTRACT: Since the 1970s, the population of the Japanese eel Anguilla japonica has dramatically declined in East Asia. Consequently, conservation and resource management of this species are urgently required. However, the population genetic structure of this species, in temporal and spatial scales, is still poorly understood. We used 8 polymorphic microsatellite DNA loci to investigate its genetic composition. For cohort analysis, juvenile (glass) eels were collected yearly between 1986 and 2007 from the Danshui River, Taiwan; for arrival wave analysis, glass eels were collected monthly from Fulong Estuary, Taiwan; and for spatial analysis, glass eels were collected from Taiwan, China, Korea and Japan. Genetic differentiation among annual cohorts, arrival waves and spatial samples was very low; a significant difference was observed among annual cohorts and spatial samples, but not among arrival waves. However, specific temporal or spatial scale patterns were not seen in either pairwise genetic comparisons or the phylogenetic tree of all samples. Occasional genetic variations among samples occurred randomly, but a stable lasting genetic structure could not be formed. The isolation by distance (IBD) test showed no evidence of genetic structuring at the spatial scale, and the results of the isolation by time (IBT) test were insignificant among arrival waves. Genetic heterogeneity over a 21 yr time scale showed marginal significance, potentially reflecting a genetic drift in the Japanese eel. Our results suggest the existence of a single panmictic population of Japanese eel in East Asia.

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

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]

DISCUSSION Values of H O for genetic variability of the Japanese eel among spatial (Tseng et al. 2006), inter-annual (Tseng et al. 2003), and intra-annual (this study) samples were 0.758, 0.708, and 0.677, respectively. This indicates that genetic differenti- ation was highest among samples from different locations, intermediate among annual cohorts of the same habitats, and lowest among intra-annual cohorts of the same habitats. Several lines of evi- dence support the Japanese eel, although exhibit- ing spatial genetic differentiation, still being geneti- cally stable temporally at the same location. First, the overall temporal genetic variation among arrival waves of elvers in consecutive months of the same habitat was not significant. Pair-wise F ST values showed that only the pair of samples between Nov. and Dec. 2000 exhibited subtle but significant genetic variation. This might have been due to the phenomenon of genetic patchiness, in which random variations in parental contributions

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]

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.

(Received, March 08, 2006; Revised, April 23, 2006; Accepted, April 25, 2006) ABSTRACT The Japanese eel Anguilla japonica is one of the most important food fish in Taiwan. For cultivation, elvers of the eel are caught from the wild population in estuaries during their upstream migration. The relationship between recruitment timing of elvers and surface seawater temperature was analyzed based on the daily catch data of elvers in an estuary of northeastern Taiwan since 1980. It was found that most elvers recruited to the estuary during the period from December to January, with a rhythmic activity that follows the lunar cycle. However, the peak recruitment period in the years of 1986-87, 1990-91 and 1995-96 occurred in March, delayed approximately two months.