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1.
In an attempt to understand growth regulation in the Japanese eel, Anguilla japonica, we cloned insulin-like growth factor-I (IGF-I) cDNAs and examined their mRNA expression in several tissues. Two eel IGF-I (eIGF-I) cDNAs encoding preprohormones, eIGF-I-Ea1and eIGF-I-Ea2, were cloned from the liver by polymerase chain reaction (PCR). The preproIGF-Is were identical in signal peptide and mature IGF-I, but different in the E domain—eIGF-I-Ea2 mRNA was 36 bp longer than eIGF-I-Ea1 mRNA. Eel IGF-I was 83–94% identical with that of teleosts, 71% identical with that of dogfish, 87% identical with that of bullfrog and chicken, and 83% identical with that of humans. In both males and females the highest eIGF-I-Ea1 mRNA levels were observed in the liver, with detectable levels also found in the gills, heart, stomach, spleen, kidney, intestine, swim-bladder, muscle, and gonads. eIGF-I-Ea1 mRNA levels in the liver were higher in females than in males whereas in the intestine they were lower than in males. eIGF-I-Ea2 mRNA was detected in all the tissues examined and at similar levels in males and females. In this experiment higher eIGF-I-Ea1 mRNA levels were observed in the liver of larger glass eels than in those of smaller fish. eIGF-I-Ea2 mRNA levels were also higher in larger eels, although they were lower than IGF-I-Ea1 mRNA levels. Both eIGF-I mRNA levels in liver were positively correlated with the body size of the␣glass eels. Intraperitoneal injection of recombinant eel GH (reGH), 0.25 μg g−1 body weight, into glass eels resulted in a significant increase in both eIGF-I mRNAs in the liver 1 day after injection compared with control fish, but no elevation was observed 2 days after injection. Incubation of liver slices with reGH at concentrations of 10, 100, and 1,000 ng mL−1 for 24 h resulted in a significant concentration-dependent increase in the levels of both eIGF-I mRNAs. Higher levels of eIGF-I-Ea1 and Ea2 mRNA were observed in the gills ofseawater-reared eels than in those of freshwater-reared fish, but no differenceswere observed in the whole kidney. These results suggest that IGF-I is involved in the regulation of somatic growth and also in adaptation of the Japanese eel to seawater.  相似文献   

2.
Furazolidone, an antibacterial drug that was once widely used in the livestock industry and aquaculture, is now prohibited in numerous countries. It is difficult to detect residual furazolidone because it is readily metabolized in animal tissues but, by using and liquid chromatography coupled with tandem mass spectrometry, its metabolite, 3-amino-2-oxazolidinone (AOZ) can be detected. Here we describe the validity of an enzyme-linked immunosorbent assay (ELISA) kit to detect AOZ in Japanese eel Anguilla japonica tissue. ELISA is capable of detecting AOZ at 1.0 μg/kg in an eel sample with excellent accuracy and precision. Our results show that ELISA is suitable for regulatory purposes and for studying the fate of AOZ residues in eel treated with furazolidone. To measure the persistence of AOZ in eel tissues, eels (1.4–6.5g) were immersed in tanks containing 2 and 10 mg furazolidone/L for 3 h, and then maintained in a tank supplying well water for the next 160 days. The half-lives of AOZ, calculated from the linear terminal part of the excretion curve, were 25.0 days in muscle and 21.6 days in liver from fish exposed to 2 mg/L furazolidone. In the eels treated with 10 mg/L furazolidone, by contrast, high levels of AOZ were detected in liver and muscle, but the half-lives of AOZ were similar to those in fish treated with 2 mg/L furazolidone. The half-lives of AOZ in eel tissues were prolonged by the condition of low water temperature.  相似文献   

3.
Recombinant Japanese eel follicle-stimulating hormone (rjeFSH) produced by methylotrophic yeast was subjected to in vivo bioassay to assess its gonadotropic activities and availability to artificially induce maturation of this species. Intramuscular injections of rjeFSH into male eels at doses of 0.1 and 1.0 U/g body weight were repeated 3 times during 12 days. The rjeFSH significantly increased plasma 11-ketotestosterone levels, and induced both testicular growth and spermatogenesis in a dose-dependent manner. These results demonstrate that rjeFSH is effective in promoting male eel gamatogenesis in vivo. Instead of scarce native eel FSH, abundant recombinant eel FSH is now ready for future application to maturation induction of Japanese eel.  相似文献   

4.
Aquaculture of Japanese eel Anguilla japonica relies upon the natural recruitment of their glass eels (juveniles); however, predation that could influence glass eel recruitment remains unknown. In the present study, we aimed to elucidate the proportion of predation on A. japonica glass eels through stomach content analysis of predatory fishes collected in the estuary region of the Tone River system and its vicinity in Japan. Species of the predated glass eels were identified by DNA barcoding. A total of 270 predatory fishes of 15 taxa was collected over 2 years. The overall proportion of predation on glass eels, genetically identified as Japanese eel, was 0.7%, but this rose to 2.0% when data were limited to fishes caught during the peak months of glass eel recruitment. A glass eel was found in the stomach contents of a channel catfish Ictalurus punctatus, an invasive species in this river system, and a blackfin sea bass Lateolabrax latus. These fishes are therefore considered potential predators of A. japonica glass eels. However, as the proportion of predation was low, and the glass eels represented only small proportions of predator stomach contents, further investigation is needed for a better understanding of predation on A. japonica glass eels, and its effects on the early life stages of this endangered species.  相似文献   

5.
For efficient production of Japanese eel Anguilla japonica eggs, knowledge of the status of the sexual maturity of potential broodstock females is important because this status directly influences the time required to produce mature eggs by successive hormone doses. Here we apply an eye index (relative eye size) to evaluate the gonadal status of feminized A. japonica, which were induced by administration of estradiol-17β. Examination of gonad somatic and eye indexes of 267 feminized eels, cultivated for 12–56 months, revealed a significant correlation between these two indexes. Artificial maturation of 35 feminized eels showed that the number of hormone injections administered before ovulation was significantly lower as the eye index score increased, indicating availability of this noninvasive method of predicting sexual maturity of feminized eel. There was no correlation between eye index and fertilization rate, hatching rate, or larval survival rate, suggesting that sexual maturity before hormonal treatment does not affect egg quality.  相似文献   

6.
The initial appearance and the development of Leydig cells (LCs), the sites of steroid hormone production in the testis, were investigated ultrastructurally during testicular differentiation in the Japanese eel, Anguilla japonica. In addition, the effects of a single injection of human chorionic gonadotropin (HCG; 5 IU g body weight-1) on histological changes of the testes and serum 11-ketotestosterone (11-KT) were examined at various stages (15–18, 20–23, 26–29, 32–35, 38–41 and 46–50 cm body length (BL)) of testicular differentiation. Testicular differentiation was morphologically characterized by the development of loose connective tissue on the medial side in animals 18–29 cm in BL. Ultrastructurally, LCs were first identified in the loose connective tissue of the testis of the 23 cm fish. In the testes of fish over 32 cm, clusters of LCs were distributed throughout the interstitial region accompanying the increase in number of spermatogonia. In fish larger than 32 cm, spermatogenesis was induced by administration of HCG; serum 11-KT levels were also raised. On the other hand, there was no effect on spermatogenesis or serum 11-KT levels in fish less than 29 cm, or in the controls. These result suggests that morphological differentiation of LCs occurs in testis of the 23 cm eel, and subsequently, the testes of eels of BL more than 32 cm acquire the capability to produce steroid hormones.  相似文献   

7.
The eel has long been esteemed as an important food fish in the world, especially in Japan, and has been used as an experimental fish for many fields of fish physiology. However, the decreases in eel resources have been a serious concern in recent years. The catches of glass eels as seedlings for aquaculture have shown a long-term decrease in both Europe and East Asia. To increase eel resources, the development of techniques for artificial induction of maturation and spawning and rearing their larvae have been eagerly desired. Recent progress of reproductive physiology of fish, especially mechanisms of oocyte maturation and ovulation in female and of spermatozoa maturation in male, facilitate to establish techniques for hormonal induction of maturation and spawning in sexually immature eels. With persistent effort to development of rearing techniques of larvae, we have first succeeded to produce glass eel. These applied techniques are may contribute to understand the basic reproductive physiology of the eel.  相似文献   

8.
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.  相似文献   

9.
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10.
鳗鲡繁殖生物学研究进展   总被引：3，自引：0，他引：3  
鳗鲡是优质养殖鱼类,但鳗鲡苗种完全依靠天然捕捞。近年来鳗鲡苗种的短缺限制了鳗鲡养殖业的进一步发展,开展鳗鲡人工繁殖技术研究势在必行。文章从鳗鲡的催熟与催产、产后鳗鲡的某些繁殖生物学以及鳗鲡胚胎和仔鱼发育等方面简要回顾了鳗鲡繁殖生物学的研究概况,并着重介绍了日本的最新研究进展,日本已将人工苗培育至20多厘米的成鱼,实现了实验室内鳗鲡由卵到成鱼的全人工养殖。文章最后指出人工育苗中存在的问题,并提出今后应从内因和外因两方面研究,才能真正实现鳗鲡苗种规模化生产。  相似文献   

11.
Wild‐catch eels with low fat content are either not accepted at all or accepted as a lower‐quality and less valuable product in the global eel market. This study was undertaken with the goal of increasing the fat content of yellow shortfin eel, Anguilla australis (104 ± 11 g initial weight), captured in the wild and kept in captivity for a short period, as well as assessing their rate of growth. An 86‐d feeding trial was conducted indoors in a recirculation aquaculture system, at 25.5 ± 1.6 C. Two commercial extruded dry feeds were tested; one formulated for European eel and one not specifically intended for use on eels. Good values of specific growth rate (1.10 and 1.12%/d) and feed conversion ratio (1.01 and 1.10) were achieved with both tested feeds. At the end of the trial, eels achieved 20–22% total fat, starting from wild fish with 7% fat content. Fat quality of the fattened eel was appreciably superior (higher proportion of omega‐3 fatty acids) than the fat of eels captured in the wild. The results of this study are encouraging for the prospect of fattening yellow shortfin eels and obtaining a market‐oriented eel product.  相似文献   

12.
The rice field eel, Monopterus albus (Zuiew), is an important aquaculture fish in many Asian countries. Productivity, however, is limited by low fecundity as a result of sex reversal of female juveniles of this fish. This study was conducted to investigate the effects of estradiol valerate on the sex reversal process of this fish by determining sex changes of initial 2‐yr‐old female eels (26.5 ± 2.6 cm, 21.9 ± 2.1 g) treated with three concentrations of estradiol valerate: 0 mg/kg (Control, Group A), 10 mg/kg (Group B), and 50 mg/kg (Group C). In Group A, sex reversal took place with significantly higher percentage of sex change: about 45% of female eels to intersexes and males. Only about 22% of female eels changed to intersexes and males in Group B, but no sex reversal occurred in Group C during the experimental period. The result also indicated that the gonadal development and the concentrations of serum estradiol (E2) and testosterone (T) varied significantly with different concentrations of dietary estradiol valerate. Serum T significantly reduced but serum E2 significantly increased in Group C compared to the control Group A. The results demonstrated that estradiol valerate affected the secretion of sex steroid hormones in rice field eels and thus inhibited the sex reversal process at a low concentration (10 mg/kg) or stopped the sex reversal process at a high concentration (50 mg/kg) of estradiol valerate. These results suggest that a higher yield of mature female eels could be achieved by treatments with estradiol valerate, thus enhancing the fecundity of this rice field eel.  相似文献   

13.
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14.
美国金鳟和日本鳗鲡精浆的化学组成和渗透压   总被引：4，自引：1，他引：3  
本研究采用原子吸收分光光度法(AAS)和气相渗透压仪测定了人工养殖美国金鳟和日本鳗鲡精浆的化学组成和渗透压。研究结果表明,Na+、K+是精浆中的主要离子,可能在维持精浆渗透压和精子活动能力中有重要的作用。人工养殖美国金鳟与日本鳗鲡相比,精浆离子含量各项指标除K含量较高之外(P<0.01),其它各项指标均无显著性差异。本实验的两种鱼与其它种类海淡水鱼类比较,各种离子含量均较高;美国金鳟精浆渗透压值与其它鱼类相似,均保持在300 mOsm/kg的水平。  相似文献   

15.
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16.
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   

17.
Nonspecific responses of Japanese eels to environmental stress were monitored by assaying various lytic activities in eel epidermal extract. In fish maintained at 10 and 30 °C for up to 10 days, epidermal proteolytic activities due to serine protease and aminopeptidase and hemolytic activity varied within a 2-fold value range. Other proteolytic activities, due to cathepsins B and L, in the fish at 30 °C increased for up to 8 days and were 3.4 and 2.9-fold over those in fish maintained at 10 °C, respectively. This was accompanied by a 3.0-fold increase in bacteriolytic activity. Other forms of stress were exerted on the fishes by immersing them in a suspension of Flavobacterium columnare or giving them intraperitoneal injections of Edwardsiella tarda over 72 h. Although serine protease and aminopeptidase activities and hemolytic activity in the fishes exposed to F. columnare changed marginally, and were similar to those in the control fish, cathepsins B and L activities in the infected fishes increased more than 1.5-fold over their initial values over a 48 h period, along with a 4.5-fold increase in bacteriolytic activity. No marked change was detected in any of the lytic activities of the fishes exposed to E. tarda. These findings indicate that epidermal cathepsins B and L probably participate in bacteriolysis associated with Japanese eel skin and that their activities are elicited by environmental stimuli and may be an important nonspecific response of eels. Abbreviations: Cbz – carbobenzoxy; MCA – 4-methylcoumaryl-7-amide.  相似文献   

18.
Bacteria with lethal effect on eel larvae were isolated from moribund captive‐bred eel larvae and their 16S rRNA gene sequences were analysed. Nucleotide sequence of 10 isolates showed highest similarity with Lacinutrix algicola, Crocinitomix catalasitica and Pseudoalteromonas rubra. Age‐dependent changes in the susceptibility of eel larvae were observed in response to challenge by a highly lethal isolate. Compared with 10 and 11 days after hatching (DAH), larval susceptibility to the highly lethal isolate was lower at 18 DAH. We found that the bacterial isolates have lethal effect on the captive‐bred eel larvae, especially at the early developmental stage. These results will be useful to establish appropriate culture practices for eel larvae that will improve the success of mass production of glass eels for aquaculture.  相似文献   

19.
为证明日本鳗鲡(Anguilla japonica)生活史最后一步一产后鳗的命运,本研究模拟产后的日本鳗鲡继续在海水中养殖,观察其存活率及繁育情况.结果表明,产后鳗在海水中停食约18 d后,体能得到恢复,部分亲鱼开始出现摄食,1个月左右全部恢复摄食,经244 d养殖,雌、雄鳗体质量增加,存活率达94.6%.随后,给产后鳗注射外源性促性腺激素(鲤鱼脑垂体匀浆CPE和人绒毛膜促性腺激素HCG)后激发其退化的性腺(卵巢和精巢)重新发育(与当年银鳗作对照).通过性腺组织切片观察产后鳗和对照鳗性腺发育成熟的全过程及其差异,发现产后鳗起初性腺发育比当年银鳗差,但经多次注射激素后,产后鳗性腺成熟与当年银鳗同步,证明产后鳗生殖细胞对激素的敏感件高.应用17α,20β-双羟孕酮和促性腺激素释放激素类似物(GnRH-A3)使催熟的产后鳗和对照鳗均产卵和排精,并孵化出仔鱼,从而有力地证明,鳗鲡产后虽体质弱,但待体能恢复后能够继续生存和繁殖.本研究旨在探讨利用产后鳗作为今后鳗鲡人工繁殖亲鳗的可行性.  相似文献   

20.
Serum biochemical parameters are important aspects in the management of endangered species, such as Acipenser persicus. The values of these parameters can be used for confirming the maturity and for monitoring any changes in the quality of waters and related soils. Serum samples of 44 A. persicus fishes were analyzed and their serum parameter values were determined as Mean±SD in four groups: mature males and females and immature males and females, respectively. We compared the levels of calcium (Ca; 1.97 ± 0.31–2.38 ± 0.28 mmol/l), blood urea nitrogen (BUN; 4.4 ± 0.54–6.16 ± 0.63 mmol/l), cholesterol (CHO; 2.55 ± 0.42–3.51 ± 0.65 mmol/l), creatinine (CREA; 27.23 ± 3.5–83.98 ± 7.5 mmol/l), magnesium (Mg; 2.74 ± 0.18–3.05 ± 0.46 mmol/l), bilirubin (Bilirubin; 2.05 ± 0.42–13.93 ± 4.39 μmol/l), aspatate transaminase (AST; 18.25 ± 1.5–167 ± 38 Iu/l), alanine transaminase (ALT; 11 ± 1–25.33 ± 9.24 Iu/l), alkaline phosphatase (ALP; 183.5 ± 17.68–523 ± 66.23 Iu/l) and creatine kinase (CK; 157.5 ± 27.58–2132.2 ± 250.92 Iu/l). We have shown that there were no differences in the Ca and Mg levels among the different groups. However, mature females have higher CREA, AST, CHO and lower BUN, ALP and ALT than the immature females. In the mature males, the values of ALP and bilirubin were higher yet the values of CREA and ALT were lower than in the immature males.  相似文献   

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