Effects of temperature on vitellogenesis in Japanese eel Anguilla japonica

ABSTRACT:   Cultured immature female Japanese eels acclimated to sea water at either 10 or 20°C were treated weekly with salmon gonadotropin fraction (sGTH) in order to investigate the effects of water temperature on artificial induction of ovarian maturation. In eels maintained at 20°C, ovulation was induced in 11 of 18 fish during the experimental period of 13 weeks, whereas at 10°C all fish showed a low gonadosomatic index (GSI) at the end of the experiment. Plasma vitellogenin levels were higher in eels kept at 20°C than in eels at 10°C throughout the experiment. However, no significant differences were observed in the plasma testosterone and estradiol-17β levels between groups. Eels pretreated with sGTHs at 10°C for 13 weeks were separated to two different temperature (10 and 20°C) groups, and received the same weekly sGTH injections. In eels transferred to 20°C, plasma vitellogenin levels, GSI and oocyte diameter were increased, but these values were maintained at low levels in eels that remained at 10°C. These results clearly indicate that water temperature is an important factor regulating vitellogenesis in the Japanese eel.     

日本鳗鲡排卵的人工诱导

对日本鳗鲡(Anguillajaponica)卵巢发育的时间与催产率的关系进行研究,对卵母细胞在体内胚泡破裂(GVBD)的发生过程、以及用17α-OHP和17α,20β-DHP诱导日本鳗鲡排卵的方式、时机和催产效果进行观察,结果表明,卵巢发育时间越长,催产率越低。造成催产率低的原因主要是由于日本鳗鲡在卵母细胞成熟后期,雌鳗个体对催产药物敏感性差异较大,催产时机难以掌握。通过采用适合日本鳗鲡卵母细胞的透明液观察GVBD的发生过程,并根据每个个体GVBD的发生速度,制订适宜的催产方案基本解决了上述难题。本实验采用CP、HCG、17α-OHP或17α,20β-DHP混合催产,使其平均催产率由35 4%分别提高到91 9%和93 0%。17α-OHP和17α,20β-DHP的催产剂量为5mg/(500g)和10mg/(500g)。在(21±0 5)℃水温条件下,催产效应时间分别为15～18h和13～16h。     

Genetic variability of the Japanese eel Anguilla japonica (Temminck & Schlegel) related to latitude

Abstract— Isozyme genotypes of 400 glass eels recruiting to 4 localities along the east Asian coast, stretching from Taiwan to the Yalu River of northeastern China, were studied using starch gel electrophoresis. Geographic cline was found to exist in two loci: NADP-isocitrate dehygenase-1 and 6-phosphogluconate dehydrogenase. Frequencies of the most common allele of these two loci increased from south to north. In the latitudinal range of 25°N to 40°N, the magnitude of difference of IDH100 and PGD100 was 13% and 9% respectively. However, deviations from Hardy-Weinberg equilibrium were found to be insignificant in both loci at three of the four localities. The cline was, therefore, unlikely to have resulted from selection. Migration time-lag from different parts of the continent to the spawning ground in the western Pacific was suggested to be a possible reason for the formation of the cline.     

Development of an emulsion prepared with lipophilized gelatin and its application for hormone administration in the Japanese eel Anguilla japonica

A new water-in-oil-in-water (W/O/W) type emulsion using lipophilized gelatin (LG) and cotton-seed oil was developed for a novel method of hormone administration in fishes. LG was prepared by attaching palmitic anhydride to gelatin. The best conditions for preparing stable emulsions were determined where the final concentrations of LG in the emulsion and the volume ratio of LG solution to cotton-seed oil were 2% and 1:2, respectively. Hormone releasing properties of LG emulsion were compared with a water-in-oil (W/O) type emulsion prepared with Freund's incomplete adjuvant (FIA) and saline solution by monitoring plasma profiles of salmon gonadotropin (sGtH) II in the Japanese eel. sGtH II is gradually released from the LG emulsion. LG emulsion had hormone-releasing properties different from those of the saline solution and the FIA emulsion. Immature female Japanese eel (BW, 566 to 1017 g) received a weekly intramuscular injections (total of 10 injections) of the LG emulsion, the FIA emulsion or the saline solution, each of which contained sGtH fraction. The LG emulsion was found to be more effective in inducing ovarian maturation. In mature eel, final maturation and ovulation could be induced by simultaneous administration of sGtH fraction and 17-hydroxyprogesterone using LG W/O/W emulsion.     

Fine structure and differentiation of the alimentary canal in captive-bred Japanese eel Anguilla japonica preleptocephali

ABSTRACT:   The fine structure of the alimentary canal in preleptocephali produced by artificially matured Japanese eel was examined. At 1 day posthatch (dph), the alimentary canal was found only above the dorsal side of the yolk mass, and the epithelium was composed of a single layer of epithelial cells. By 5 dph, the alimentary canal was divided into three segments based on the structure of the epithelial cells: foregut, midgut and hindgut, corresponding to the future esophagus, intestine and rectum, respectively. After 7 dph, the epithelium in the foregut was surrounded by a circular muscle layer, suggesting a role in the transportation of food materials. The epithelial cells of the midgut exhibited well-developed membranous structures, which are deduced to be invaginations of the cytoplasmic membrane. Pinocytotic invaginations and vacuoles were observed in the epithelial cells of the hindgut; this observation suggests that this region is involved in the uptake of food. Significant changes in morphological features of the epithelial cells in each segment were observed until 7 dph; however, these were not evident between 7 dph and 13 dph. Consequently, the differentiation of the alimentary canal was completed by 7 dph, and preleptocephalus had developed the ability to absorb food by 7 dph.     

Ultrastructure of the oocytes of the Japanese eel Anguilla japonica during artificially induced sexual maturation

ABSTRACT: Morphological changes in the oocytes of the Japanese eel, Anguilla japonica , induced to undergo ovarian development by repeated injections of salmon pituitary homogenate, were examined using electron microscopy. Oil droplets were closely associated with organelles, especially mitochondria, and increased in number as oocyte growth proceeded. They fused at the migratory nucleus stage. During vitellogenesis, two types of cortical alveoli were distinguished, one having filamentous contents, the other having latticated contents. As oocytes reached maturity, the structure of the cortical alveoli was exclusively filamentous. Yolk globules were homogeneous and highly electrondense, but electrondensity decreased during hydration. The structure of the zona radiata of previtellogenic oocytes consisted of two layers, and an additional reticular network structure was formed on the inside of the zona radiata during the vitellogenic stage. The zona radiata lost the reticular network structure and assumed a layered structure of uniform electrondensity at the migratory nucleus stage. These structural changes during oocyte development were mostly comparable to those in other teleosts. Results of the present study should assist in developing improved methods for full control of artificial maturation in the Japanese eel.     

Cardiovascular,respiratory, and blood adjustments to hypoxia in the Japanese eel,Anguilla japonica

The cardioventilatory performance of the Japanese eel,Anguilla japonica, was evaluated during acute exposure to hypoxia. The eel became an oxygen conformer as ambient PO₂ fell below the critical value of 110 mmHg. Although arterial and venous PO₂ also fell progressively, the arterial O₂ content remained constant down to an ambient PO₂ of about 60 mmHg. Arterial blood O₂ saturation was maintained at 85% even at 40 mmHg. The increase in the supply of O₂ to the animal during hypoxia was due to a combination of adaptive adjustments: (1) an increase in ventilation: perfusion ratio brought about mainly be bradycardia; (2) an increase in respiratory exchange surface area which was manifested as an increase in branchial blood transit time and quantified as a rise in transfer factor, water-blood overlap coefficient and utilization (%); (3) an increase in blood O₂ affinity and capacitance coefficient as a result of respiratory alkalosis and Bohr-Root shift and a decrease in haemoglobin allosteric modulator (GTP, ATP) concentrations in the RBC. These factors together helped to increase the efficiency of O₂ transfer across the gills.     

日本鳗鲡人工繁殖研究现状及存在问题

鳗鲡属(Anguilla)鱼类共有19个种和亚种,其中以日本鳗鲡(A.japonica)和欧洲鳗鲡(A.anguilla)的人工养殖最为广泛。鳗鲡主要生长于热带及温带地区水域,除了欧洲鳗鲡及美洲鳗鲡(A.     

鳗鲡繁殖生物学研究进展

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。     

中草药添加剂对日本鳗鲡生长和非特异性免疫效应的研究

在基础饲料中分别添加0.5 g/kg、1.0 g/kg和1.5 g/kg的自制中草药免疫添加剂,配制成3种试验饲料,以基础饲料为对照组饲料,每处理设3个平行样,对体重为30~40 g的日本鳗鲡(Anguilla japonica)进行为期60 d的饲养试验,每20 d取样一次,以相对增重率、成活率和血清中的溶菌酶(LZM)、一氧化氮合酶(NOS)、碱性磷酸酶(AKP)和超氧化物歧化酶(SOD)活性为指标,探讨了中草药免疫添加剂对日本鳗鲡生长和非特异性免疫效应的影响。结果显示:饲料中添加中草药免疫添加剂可以显著提高日本鳗鲡的增重率,降低饲料系数(P<0.05)。试验组日本鳗鲡血清中的LZM、NOS、AKP和SOD等活性均高于对照组。因此,中草药免疫添加剂具有显著促生长和增强机体免疫能力的作用,建议在实际生产中的添加量为1.0 g/kg较为合适。     

Population structure of the Japanese eel Anguilla japonica as examined by mitochondrial DNA sequencing

SUMMARY: To examine the population structure of the Japanese eel Anguilla japonica , mitochondrial DNA sequence analysis was made for various samples of glass eels that might reflect genetic characteristics of spawning aggregates. The mitochondrial DNA from a total of 51 glass eels collected at Tanegashima Island, Kanagawa and Ibaraki in different periods within an inshore migrating season was sequenced for a 615 base-pair fragment from the tRNA^Thr gene to the central part of the control region. The DNA region was so variable that no individual was found to possess the same sequence, although average sequence differences within samples (1.07–1.63) were not large. Average sequence differences between samples (1.22–1.57) were comparable to those within samples, suggesting no genetic heterogeneity among samples. Tree analysis of the sequences showed neither a geographical nor temporal structure of population. Furthermore, although all DNA sequences from the present study were different from one another, two sequences were found to be the same with those reported from individuals collected in different localities in different years. Altogether, the present mitochondrial DNA sequence analysis of glass eels did not provide any evidence for genetic subdivision of the Japanese eel population.     

长江口降海洄游鳗鲡的年龄结构与生长特征

日本鳗鲡是亚洲具有重要经济价值的降海洄游鱼类,长江口是我国鳗苗的主产区和仅存的成鳗渔业水域。研究分析了2008年9-11月采自江苏靖江段(31°30′N,120°42′E)的153尾银色鳗样本的年龄和生长参数。结果显示,长江口降海洄游的鳗鲡群体雌性由3～7(平均5.52)龄组成,雄性由3～5(平均4.38)龄组成,雌性群体的年龄结构高且多于雄性群体。雌雄鳗鲡的最大年增长均出现在4龄,但雌性个体的生长拐点年龄ti=5.20、拐点体长lr=683.05mm、拐点体重Wr=546.37g、平均渐近体长L∞=1011.03mm和体重W∞=1830.16g,均显著大于雄性个体的生长拐点年龄ti=4.91、拐点体长lr=517.15mm,拐点体重Wr=216.15g、平均渐近体长L∞=750.30mm和体重W∞=715.90g。研究还表明,长江口降海洄游鳗鲡的群体平均年龄比我国其他地区和日本的均要低,但平均渐近体长却明显要大于其他分布地,预示着长江更适合于鳗鲡的生长和性腺成熟。