Maturation and reproductive cycle of female armorhead <Emphasis Type="Italic">Pseudopentaceros wheeleri</Emphasis> from the southern Emperor—northern Hawaiian Ridge Seamounts

ABSTRACT:   The stage of ovarian development and annual reproductive cycle of female armorhead Pseudopentaceros wheeleri collected from seamounts of the southern Emperor–northern Hawaiian Ridge in 1993 and 1995–1996 was investigated through use of the gonadal somatic index ( GSI ) and ovarian histology. The stages of oocyte development were classified into eight developmental stages (perinucleolus, cortical alveolus, oil droplet, early yolk globule, late yolk globule, migratory nucleolus, prematuration, and maturation) based on histological characteristics. Oocytes of different size and developmental stage were present within ovaries during the spawning season. Oocyte development appears to be asynchronous and armorhead apparently spawn several times during the spawning season. The stage of the most developed oocyte was used to classify the stage of ovarian maturation. The GSI increased gradually with ovarian development. Oocytes in the perinucleolus, cortical alveolus, and oil droplet stages were present in ovaries throughout the year. Early and late yolk globule stages appeared during August–September indicating that yolk formation begins during late summer. The migratory nucleolus through maturation stages were detected during November–January. Post ovulatory follicles were present during November–March, and GSI values rapidly decreased in February. Results indicate that spawning occurs during November–February and peaks during December–January.     

波纹龙虾卵巢的解剖学与组织学研究

试验结果表明,波纹龙虾卵巢呈H状,位于消化道的背面,随着卵巢的发育颜色依次为乳白色、淡橙色、橙色和橙红色.卵子发生分为4个时期(8个亚期):增殖期(卵原细胞期)、卵黄合成前期(束状期、染色质核仁期)、卵黄合成期(油球期、卵黄板形成前期、卵黄板形成期、成熟前期)和成熟期;卵巢发育分为6个时期:增殖期、发育期、成熟前期、成熟期、排卵期和恢复期.     

Annual changes in ovarian development and plasma estradiol-17β level in reared female common Japanese conger, <Emphasis Type="Italic">Conger myriaster</Emphasis>

ABSTRACT:   Annual changes in the gonadosomatic index (GSI), oocyte diameter, gonadal histology and plasma estradiol-17β (E₂) levels were investigated in female common Japanese conger Conger myriaster in captivity. Juveniles were caught in September 1999 and reared in seawater at temperatures ranging from 10–20°C for 3 years. All fish were immature when captured in September 1999. GSI and oocyte diameter increased from October 2000, peaked between summer and autumn 2001, and bottomed-out in winter 2001. Plasma E₂ level also increased from October 2000, but remained high. The ovarian developmental stage was at the peri-nucleolus stage or the oil droplet stage until September 2000. Vitellogenesis started in October 2000 and oocytes progressed to the tertiary yolk globule stage by summer 2001. However, vitellogenic oocytes regressed in all females after autumn 2001. The neogenetic oocytes began to increase after November 2001 and ovarian development progressed in 2002 as they did in 2001, although maximum GSI in 2002 was half its 2001 value. These data indicate that ovarian development in the common Japanese conger has an annual periodicity, and that these congers may be able to spawn in multiple years under rearing condition.     

Reproductive cycle and human chorionic gonadotropin-induced ovulation in hatchery reared Japanese catfish Silurus asotus

ABSTRACT:   The annual reproductive cycle, including the first maturity of ovarian development and plasma levels of testosterone (T) and estradiol-17β (E2), was examined in female Japanese catfish Silurus asotus reared under natural conditions. In addition, the possible period that final oocyte maturation and ovulation can be induced by human chorionic gonadotropin (hCG) injection were investigated. Results showed that female Japanese catfish matured 1 year after hatching under reared conditions. The beginning of vitellogenesis was in March and ovarian development and plasma T and E2 levels peaked in June. Thereafter, the gonadosomatic index gradually decreased to October and regression of oocytes at the tertiary yolk globule stage was observed. Female Japanese catfish could be induced to final oocyte maturation and ovulation by hCG treatment during the period from June to September. In addition, the fertilization rates were relatively high and stable during this period. These results suggest that yearling female Japanese catfish can be used as brood stock for seed production. This is the first study to investigate the annual reproductive cycle in Japanese catfish. These data will provide useful information regarding brood stock management and seed production.     

Histological observations of seasonal reproductive and lunar-related spawning cycles in the female honeycomb grouper Epinephelus merra in Okinawan waters

Seasonal reproductive and lunar-related spawning cycles of the female honeycomb grouper Epinephelus merra inhabiting Okinawan waters were examined by histological observation of ovaries. Gonadosomatic index (GSI) increased beginning in May and peaked in June. Histological observations revealed that many oocytes laden with yolk were present in the ovaries from May to August. From September to October, ovaries were occupied by immature oocytes. These results suggest that the reproductive season of E.   merra lasts for 4 months from May through August in Okinawan waters. When the fish were collected according to the lunar cycle, GSI increased with the approach of the full moon. Oocytes at various development stages were observed from the first quarter to the full moon. Fresh ovulatory follicles were present in the ovaries around the last quarter moon. These results suggest that E.   merra has a lunar spawning cycle and spawns between the full moon and the last quarter moon. Ovarian features of the fish collected around the last quarter moon were different among individuals; some fish had many oocytes at the tertiary yolk stage in the ovaries, while the ovaries of the others were occupied by the oocytes at the peri-nucleolus and the oil droplet stages. This observation suggests that a minor release of eggs occurs in this species before or after a major spawning lunar day. Oocytes at the migratory nucleus and the maturation stages were not observed in any ovarian samples. This may mean that maturation of oocytes is related to the spawning behavior of this species and makes rapid progress in the process of aggregation at the spawning sites.     

A preliminary experiment regarding the natural induction of gonadal development in female Japanese eels without hormone treatment

To test whether gonadal development of female eels could be promoted without any exogenous hormone treatments, we observed the effect of water temperature manipulation. After 3–5 months of water temperature treatments, three silver eels showed higher gonadosomatic indices (GSI). In particular, one eel in the 5–15°C fluctuating temperature treatment group (5°C daytime and 15°C night‐time) had the highest GSI of 8.5 with secondary yolk globule stage oocytes of large diameter (OD; 412 μm) after 3 months, which indicated definite gonadal development compared with those in the initial states (mean GSI, 2.4; OD, 226.7 μm). The 5–15°C fluctuating temperature and constant 5°C groups had low oocyte breakdown (atretic) rates. Because daily temperature fluctuations and cold daytime water are experienced by vertically migrating silver eels in the ocean, these temperature conditions may be key maturation process components that could be useful for hormone‐free artificial maturation.     

Diurnal rhythm of serum steroid hormone levels in the Japanese whiting,Sillago japonica,a daily-spawning teleost

Ovarian developmental stages and serum steroid hormone levels were examined at six different times of day (0100, 0600, 1000, 1300, 1600, 2000 h) in a marine teleost, the Japanese whiting Sillago japonica, which has an asynchronous-type ovary containing oocytes at various stages of development and spawns every day during a period ranging up to three months. The largest oocytes in the ovaries at the active vitellogenic or post-vitellogenic stages were found between 0100 and 1300 h. Oocyte maturation indicated by germinal vesicle breakdown (GVBD) occurred at 1600 h, and ovulated oocytes were observed in the ovaries collected at 2000 h. These processes were accompanied by a significant daily change in serum steroid hormone levels. The serum level of estradiol-17β showed a peak in fish with mature oocytes sampled at 1600 h. In these fish, the second-largest oocytes in the ovaries were at the initial stage of vigorous vitellogenesis, the secondary yolk stage. Therefore the highest level of serum estradiol-17β was considered to be due to the second-largest oocytes. Testosterone levels remained low and constant throughout the experimental period. The serum levels of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) peaked at 1600 h at which time all fish had mature oocytes. These results indicate that the Japanese whiting possesses a diurnal rhythm of oocyte development including vitellogenesis, oocyte maturation and ovulation, and further suggest that daily cycles in oocyte growth and maturation which simultaneously take place in an ovary are regulated by diurnal secretions of estradiol-17β and the maturation-inducing steroid, 17α,20β-diOHprog.     

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.     

养殖金乌贼卵子发生和卵巢发育的组织学观察

为了深入了解金乌贼(Sepia esculenta Hoyle)的生殖生理特性,本研究采用解剖学方法及组织切片技术,观察和描述了金乌贼卵巢形态和卵子各个时相结构特征及其变化规律。研究结果表明,金乌贼卵子发生过程的主要特征表现为,卵子成熟之前滤泡细胞一直存在且伴随着其结构变化,滤泡细胞解体与卵黄物质出现同步发生,卵黄物质从无到有再到大量积累直至充满整个卵母细胞,细胞核则随着滤泡细胞内折逐渐发生偏移直至最后消失。研究还发现金乌贼卵巢内卵子发生不同步且形态差异显著,未成熟的卵子粘连在卵巢基质上,依次环布于卵巢基质周围,越靠近中心,卵母细胞发育程度越低;成熟后的卵子游离在卵巢腔中,经过输卵管排出体外。根据卵巢内卵子的大小和形态、滤泡细胞形态及卵黄形成情况,将金乌贼卵子发生分为增殖期(卵原细胞期)、小生长期(无滤泡期,单层滤泡期,双层滤泡期)、大生长期(滤泡内折期,卵黄形成早期,卵黄形成晚期)、成熟期、退化吸收期共5个时期9个时相。卵巢发育分期则是以卵子时相为基础,根据卵巢的外观形态、性腺系数以及切面上优势卵子的时相,把卵巢分为Ⅰ~Ⅵ共6个时期。金乌贼卵巢发育和卵子发生的动态观察与描述,对丰富头足类繁殖生物学理论及提升人工繁殖技术都具有重要意义。     

Effects of silvering state on induced maturation and spawning in wild female Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis>

ABSTRACT:   The effects of silvering state of wild female Japanese eels Anguilla japonica on the success of induced maturation and the following spawning were examined. Thirty-eight females, collected in Mikawa Bay, were divided into four stages based on their silvering state: yellow (Y1), late-yellow (Y2), silver (S1) and late silver eels (S2). Despite injections of salmon pituitary extract (SPE) through the standard technique, Y1 and Y2 eels did not respond to the treatment with undeveloped gonad (gonad-somatic index [GSI]: 0.3–0.9), and all these females died by 5 weeks, probably due to an abnormal physiological condition. Most S1 (81%) and S2 eels (100%) matured completely (GSI: 17.8–51.4), and finally spawned successfully (69% for S1, 89% for S2). S2 eels fully matured with oocytes of over 750 μm in diameter by significantly smaller number of injections of SPE (5–6 times) than the case of S1 eels (6–8 times). The amount of eggs released by S2 eels (0.65 ± 0.11 g/fish per body weight [BW]) was significantly larger than those by S1 eels (0.54 ± 0.09 g/fish per BW). There was no difference in fertilization and hatching rates between eggs released by S1 eels and those of S2 eels. These results indicate that the success of induced maturation and spawning in wild female Japanese eels depends on their silvering state, and matured eggs can be obtained efficiently through the use of S2 eels rather than other stages.     

日本囊对虾卵母细胞发育过程中组织蛋白酶C比活性测定

组织蛋白酶C是一种溶酶样半胱氨酸蛋白酶，近年我们报道了组织蛋白酶C的表达与日本囊对虾(Marsupenaeus japonicus) 卵母细胞最后成熟阶段密切相关，本研究对卵母细胞发育主要不同时相特别是卵母细胞最后生理成熟过程进行了连续观察，测定了组织蛋白酶C在卵母细胞发育过程中的比活性。结果表明，日本囊对虾卵母细胞发育可划分为9个时相，即卵原细胞时相、核仁时相、周边核仁时相、初级卵黄发生时相、次级卵黄发生时相、皮质棒早期时相、皮质棒中期时相、皮质棒晚期时相、排卵期时相，生发泡的破裂是在排卵之前就已经发生；免疫印迹实验结果显示组织蛋白酶C蛋白只在卵母细胞最后成熟阶段即皮质棒发生时期表达，但酶活性测定结果表明组织蛋白酶C比活力在即皮质棒发生前后没有变化，酶活性较低，以上数据提示组织蛋白酶C可能与受精时皮质棒的释放以及受精卵外胶膜的形成有关。     

福建省东山岛西埔湾港养斑鰶的繁殖生物学

本文研究了福建省东山岛西埔湾港养斑鰶性腺周期发育、成熟系数周年变化、个体生殖力以及雌雄同体。港养斑鰶能在半封闭式湾内发育成熟而且自然产卵。其卵细胞发育分为6个时相,精巢发育分为6期。卵膜由透明带、外放射带和内放射带组成,内有孔道结构。第4时相中期卵母细胞的内放射带有7～8层纤维状片层。产卵后鞘膜细胞和颗粒细胞分裂增殖变成游走的吞噬细胞。西埔湾港养斑鰶Ⅰ龄鱼初次性成熟,生殖季节从12月下旬至翌年3月下旬,生殖盛期为2月,雌鱼成熟系数高达17.88％。个体绝对生殖力为7575～72621粒,平均 35310粒,系属于分批产卵类型,第1批生殖力大于第2批。     

Changes in brain and pituitary GnRH levels during ovarian maturation in wild female Japanese flounder

To elucidate the role of gonadotropin-releasing hormone (GnRH) in gonadal maturation in wild female Japanese flounder Paralichthys olivaceus, we monitored changes in the levels of seabream GnRH (sbGnRH) in the olfactory bulb, telencephalon, hypothalamus, and pituitary during ovarian development together with changes in plasma levels of testosterone (T), estradiol-17β (E₂), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP). Fish were caught offshore of the northern mainland of Japan in the Pacific Ocean at 3- to 4-week intervals between April and September by gill net. The netted fish were categorized into six groups based on ovarian stages: previtellogenic (April–early May), early yolk (April–late May), late yolk (late May–June), early spawning (June–August), late spawning (September), and termination (September) stages. The gonadosomatic index significantly increased from the previtellogenic to early spawning stages and decreased thereafter. In the olfactory bulb, no significant differences were observed in sbGnRH levels among the developmental stages. In contrast, sbGnRH levels in the telencephalon and hypothalamus were very high in the previtellogenic stage, lower in the early spawning stage, and relatively high in latter stages. sbGnRH levels in the pituitary were high in the previtellogenic stage and low in the early spawning stage. In addition, the relatively high levels of pituitary sbGnRH were found together with high plasma T, E₂, and DHP levels in fish in the late yolk stage. These results indicate that sbGnRH in the telencephalon, hypothalamus, and pituitary is involved in ovarian maturation and that sbGnRH may play an important role in the initiation of ovarian recrudescence in wild Japanese flounder.     

Changes in the immunostaining intensities of follicle-stimulating hormone and luteinizing hormone during ovarian maturation in the female Japanese flounder

The role of gonadotropin (GTH) in the reproduction of the Japanese flounder, Paralichthys olivaceus, was studied by assessing the changes in the apparent activity of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland during gonadal maturation by immunohistochemical analyses. Corresponding changes in plasma levels of testosterone (T), estradiol-17β (E₂), and 17α,20β-dihydroxy-4–pregnen-3-one (DHP) were also studied. Reared fish at the early spawning to termination stages were sampled from May to August and wild fish at the previtellogenic to termination stages were caught at 3- to 4-week intervals between April and September offshore from the northern mainland of Japan by gill nets. The gonadosomatic index of the reared fish decreased from the early spawning stage to the termination stage, while that of the wild fish increased significantly from the previtellogenic stage to the early spawning stage and decreased thereafter. In the reared fish, the immunostaining intensities of FSH and LH were high during the spawning period, accompanied by high plasma levels of T, E₂, and DHP. In the wild fish, the immunostaining intensities of FSH and LH were low during the previtellogenic stage but increased during the maturing and spawning stages. These results indicate that both FSH and LH are likely associated with oocyte maturation in the Japanese flounder.     

多刺裸腹溞孤雌溞的卵子发生

采用光镜和透射电镜技术观察多刺裸腹溞（Moina macrocopa）孤雌溞卵子的发生过程。根据卵母细胞细胞核的形态、卵黄的合成、积累情况及核物质的形态变化等观察结果,将卵子发生分为3个时期：卵原细胞期、卵母细胞期和成熟卵母细胞期。卵原细胞核大,胞质层薄,有少量线粒体分布,核物质浓缩为一团;卵母细胞发育的早期和中期细胞体积增大,细胞质层增厚,线粒体迅速增多,细胞核变圆,核物质分散成多块;后期卵母细胞胞质中开始出现大量卵黄颗粒和少量脂滴,细胞核边缘波浪化,线粒体空泡化,其中卵黄合成初期,核物质重新聚集在细胞核中央,在卵黄合成中期又分散开来;成熟卵母细胞质中充满卵黄颗粒,呈强嗜酸性,细胞核的形态呈不规则状,核物质分散。多刺裸腹溞生殖腺的外部形态随着生殖周期的变化而不同。在孤雌溞的整个生活史中生殖腺内卵子的发育经历了“同步一不同步一局部同步”的发育模式。发现1龄幼溞生殖腺中不存在卵原细胞,成龄溞的生殖腺有多个发育时期的生殖细胞并存。同时在亚显微水平上发现卵黄主要由线粒体演变而来,也通过吞饮作用吸收成熟的卵黄颗粒,内源与外源性共同作用形成卵黄。[中国水产科学,2006,13（4）：547—554]     

Swimming stimulates oocyte development in European eel

In this study, we subjected eels from Lake Balaton (Hungary) to a swimming period of 1 week and 2 or 6 weeks. Most eels were silver and were 13–21 years old. Time dependent changes in morphometrical parameters and developmental characteristics of the oocytes were determined. Already after 1 week of swimming, the gonadal mass increased and oocytes became larger, filled with large numbers of lipid droplets. After 2 and 6 weeks of swimming we found in addition a significant enlargement of the eyes, which is a sign of sexual maturation. In contrast to the resting eels, that had oocytes in the primary growth phase (stage 1–2); the swimming eels had oocytes in stage 3; the cortical alveolus or lipid droplet stage. The results indicate that lipid mobilisation induced by swimming is a requirement for the natural incorporation of lipid droplets in the oocytes, a crucial step in oocyte maturation. As the Balaton eels responded stronger to swimming than young farmed eels, it is suggested that older eels are more sensitive for maturation triggers.     

Cloning of estrogen receptor-β cDNA of common Japanese conger Conger myriaster and expression of the gene during oocyte development

ABSTRACT:   Estrogen receptor (ER) cDNA was cloned from the liver of common Japanese conger Conger myriaster . Common Japanese conger ER cDNA contains 2543 nucleotides including an open reading frame that encodes 596 amino acids, with a molecular weight of 66.1 kDa. The deduced amino-acid sequence of the common Japanese conger ER shares 85% identity with that of eel Anguilla japonica ER-β, and 39–46% and 53–59% identity with the deduced sequences of ER-α and ER-β of other species, respectively. In a phylogenetic analysis, the common Japanese conger ER was found to cluster with the ER-β of other species. The common Japanese conger ER-β also has six domains (A–F), which are conserved in the nuclear receptor superfamily. The amino-acid sequences in the C and E domains were highly conserved between common Japanese conger ER-β and other ER. However, the other domains showed low homology. In the female common Japanese conger, ER-β mRNA was highly expressed in the liver and pituitary gland. The expression levels of the ER-β gene increased from the oil droplet stage to the primary yolk globule stage and were maintained until the migratory nucleus stage.     

The reproductive biology of the amberjack, Seriola dumerilii (Risso 1810). I. Oocyte development in captivity

A study of the reproductive biology of the amberjack, Seriola dumerilii, held in captivity was carried out, describing oogenesis as well as the different stages of the ovarian cycle. Seven stages of oocyte development, as well as oogonia, were distinguished. Cortical alveoli were hardly detectable within the oocyte, as they were small, sparse and contained few mucopolysaccharides. It is suggested that their role in the fertilization process might be less important than in other teleost species. Fish aged 3 and 4 years were found to be sexually immature, with ovaries containing only previtellogenic oocytes. Vitellogenesis started in December in fish aged 4 + years. Late-developing ovaries showing deposition of yolk protein granules were found at the end of the 5th year of life (May) in specimens measuring 80.0 ± 3.5 cm standard length. This should be regarded as the minimum size at which sexual maturity is reached in S. dumerilii. Final vitellogenesis and oocyte maturation were, however, inhibited in captivity, and extensive follicular atresia took place as the natural spawning season approached. It is suggested that insufficient gonadotrophic stimulation because of confinement stress may be the cause of failed maturation and spawning in this species under culture conditions.     

The reproductive physiology of three age classes of adult female diploid and triploid brook trout (Salvelinus fontinalis)

Triploid female fish show impaired gametogenesis and are unable to produce viable offspring. The reproductive physiology of artificially-induced triploid female salmonids has been well described up until the time of first sexual maturation in diploids, but few reports exist for older triploids. This study reports the influence of triploidy on growth, ovarian development and reproductive endocrinology among three age classes of female brook trout (Salvelinus fontinalis) in comparison to sibling diploids. Triploids were larger than diploids for most of the study period, but the difference was statistically significant only during maturation and spawning of 2⁺ diploids. Plasma estradiol-17 (E₂), testosterone (T) and vitellogenin (VTG) levels in triploids were generally lower than in diploids, and VTG was the only parameter to show seasonal fluctuations resembling those of diploids. Triploids showed significantly lower GSI and total oocyte number than diploids of similar age, and only half of all triploids sacrificed during the study (n=56) had developing oocytes in their ovaries. At age 3⁺, 13 of 19 triploid females had oocytes at various stages of development, including perinucleolar, yolk vesicle and yolk globule stages. In addition, three of these fish had collectively produced 72 mature stage oocytes. Thus, whereas diploid brook trout can produce mature oocytes as two-year-olds, triploids cannot do so until four years of age, with the number of mature oocytes being greatly reduced.     

Temporal progression in migratory status and sexual maturation in European silver eels during downstream migration

The onset of downstream migration of European eels is accompanied by a cessation of feeding and the start of sexual maturation which stresses the link between metabolism and sexual maturation, also suggesting an important role for exercise. Exercise has been tested with eels in swim tunnels and was found to stimulate the onset of sexual maturation. In this study, we have investigated the interplay between migration and maturation in the field during the downstream migration of female silver eels. Temporal changes in migratory status and sexual maturation among silver eels of the upstream Rhine River system over 3 months of the migration season (August, September and October) were determined in biometrical parameters, plasma 17β-estradiol and calcium levels, oocyte histology and gonadal fat levels. Furthermore, the ecological relevant parameters age as determined by otolithometry and health aspects indicated by haematocrit, haemoglobin and swim-bladder parasite load were measured. Silver eels were estimated to be 14 years old. A strong temporal progression in migratory stage was shown over the months of downstream migration. Catches probably represented a mix of reproductive migrants and feeding migrants of which the ratio increased over time. Furthermore, this study confirmed our hypothesis linking the migratory stage to early maturation as indicated by enlargement of the eyes, oocyte growth and fat deposition in the oocytes, exactly the same changes as found induced by exercise but not ruling out environmental influences. Migrants show extensive fat uptake by the oocytes, probably stimulated by the swimming exercise. In addition, at least 83% of the silver eels in this spawning run may have suffered from negative effects of swim-bladder parasites on their swimming performance.