Role of steriod hormones in sex change of protogynous wrasse

The endocrine mechanisms of sequential hermaphroditism were investigated in protogynous wrasse, Halichoeres trimaculatus. Administration of aromatase inhibitor and androgen both stimulated sex change, while estrogen suppressed the induced sex inversion. The results suggest that removal of estrogen is a key step to initiate sex change.     

Bi-directional sex change and its steroidogenesis in the wrasse, Pseudolabrus sieboldi

The protogynous wrasse, Pseudolabrus sieboldi, is a good model for studying the physiological mechanism of sex change in teleosts. We established a way to induce sex change bidirectionally by controlling the social conditions in captivity. This is the first report of a reversed sex change in a promiscuous species. After identifying all the steroid hormones produced in the ovarian follicles and testis, and clarifying their synthetic pathways, we examined the function of the sex steroids in the sex change of P. sieboldi. We concluded that the activation of 17β-HSD-III is the first step in inducing morphological and functional change from an ovary to a testis.     

东太平洋赤道海域茎柔鱼组织能量积累及其与海表面环境因子的关系

为了从能量积累角度掌握茎柔鱼 (Dosidicus gigas) 的生活史策略,利用组织能量密度测定技术和广义线性混合效应模型 (Generalized linear mixed-effects models, GLMM) 对东太平洋茎柔鱼的肌肉、性腺等组织的相对能量积累及其与栖息海域环境因子之间的关系进行了分析。结果显示,东太平洋茎柔鱼以肌肉组织能量积累为主 (相对能量积累占70%以上),性腺组织能量积累相对较低。在生理性发育期至功能性成熟期,肌肉组织相对能量积累下降显著,性腺组织相对能量积累明显;在功能性成熟期,肌肉组织相对能量积累回升显著。肌肉组织和性腺组织的相对能量积累与栖息海域海表温度无显著相关性,但与栖息海域叶绿素 a 质量浓度存在显著的效应关系,并与采样经度分布密切相关。研究表明,东太平洋茎柔鱼在性腺发育开始后能量积累逐渐增加对生殖发育的投入分配,但在繁殖产卵期保持较好的肌肉组织状态,肌肉、性腺组织的相对能量积累更多取决于栖息海域的初级生产力。     

Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner

The wrasse, Pseudolabrus sieboldi, is a diandric protogynous labrid fish. Spawning is performed by a terminal phase (TP) male and an initial phase (IP) female between 6:00 and 9:00 h daily during two-month-long spawning season. In the present study, to investigate the roles of steroid hormones in the diurnal spermatogenesis of the P. sieboldi TP male, all steroid hormones produced in the testis were identified and the synthetic pathways of these steroids were determined. Furthermore, the circulating levels of the major steroids produced were analyzed throughout a day at 3-hour intervals during spawning season. In the testis, 11-ketotestosterone (11-KT), estradiol-17β (E2), 17,20β-dihydoxy-4-pregnane-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesized as the major metabolites. In vitro steroid biosynthesis experiments showed similar results to the circulation profiles of the major steroids. This study is the first to clarify the complete steroidogenic pathways in the gonads of a diandric protogynous species throughout its life, when combined with the results of the steroidogenesis in the ovarian follicles. This is also the first report of a clear diurnal rhythm of the steroid production corresponding to the spermatogenic process in the testis of a male teleost.     

Treatment with an aromatase inhibitor induces complete sex change in the protogynous honeycomb grouper (Epinephelus merra)

To study the mechanism of protogynous sex change in honeycomb grouper, the wild fish of both sexes and transitionals were collected for one year, and changes in gonadal structures and serum levels of sex hormones in each individual were examined. The onset of sex change was associated with low serum estradiol - 17β (E2) levels. In order to clarify whether E2 deprivation causes sex change, maturing females were implanted with the non-steroidal aromatase inhibitor (Fadrozole, AI). AI caused complete sex change from female to functional males in two and half months. The present results suggest that E2 is an important endogenous factor which regulates protogynous sex change in the honeycomb grouper.     

Germ cells during gonadal sex differentiation in the teleost

We reported previously that two isoforms of vasa mRNA and protein are present in tilapia (Kobayashi et al. 2002). One (vas-s) lacks a part of the N-terminal region found in the other isoform (vas). Both isoforms are expressed in oocytes through the embryonic stages when PGCs localize in the lateral plate mesoderm. After PGCs localized in the gonadal anlagen, vas-s expression increased and vas expression became undetectable. Expression of both isoforms was observed again after morphological gonadal sex differentiation, irrespective of genotypic sexes. These changes are in accordance with sex differences in number of gonial germ cells during this period, suggesting that molecular sexual dimorphism occurs in germ cells between both sexes during this period.     

Molecular cloning and expression of caspase-3 in the protandrous cinnamon clownfish, Amphiprion melanopus, during sex change

The caspase-3 appears to be a key protease in the apoptotic pathway. We identified caspase-3 complementary DNAs from the ovaries of the protandrous cinnamon clownfish (Amphiprion melanopus), and investigated its mRNA and proteins, and activity levels during the sex change (I, mature male; II, male at 90 days after removing of the female; and III, mature female). The nucleotide sequence of the caspase-3 cDNA was 969 base pairs in length with open reading frames encoding peptides of 282 amino acids. The caspase-3 mRNA and protein, and activity levels in stages of the mature gonad are higher than those of the development gonad stage. To understand the effect of gonadotropin-releasing hormone (GnRH) on gonad apoptosis, we examined expression of genes caspase-3 mRNA and activity level in immature cinnamon clownfish gonads after GnRH analogue (GnRHa). The findings support the hypothesis that caspase-3 expression is associated with both testicular and ovarian development, and suggests that it may play a role in the control of ovarian development in cinnamon clownfish. Also, we demonstrate that GnRH agonists stimulate caspase-3 production which can in turn stimulate apoptosis. The present study provides a framework for better understanding of the role of caspase-3 during sex change processes in fish.     

Sexual patterns and protogynous sex reversal in the rusty parrotfish, Scarus ferrugineus (Scaridae): histological and physiological studies

Gonadal histology confirmed that Scarus ferrugineus is a diandric protogynous fish. The process of protogynous sex reversal was investigated through histological observations on the gonads of females changing sex to male. This process was divided into three stages on the basis of changes in the structure of the germinal and somatic elements. Ovaries of functional females (stages IV-V) were filled with vitellogenic oocytes during the breeding season but contained no trace of spermatogenic tissue. During post-spawning period, the remaining vitellogenic oocytes began to degenerate and accompanied by a drop in plasma levels of estradiol-17β. At the commencement of sex change, previtellogenic oocytes began to degenerate and stromal cell aggregation was observed in the central region of the lamellae. At mid-reversal stage, steroid-producing cells (Leydig cells) developed at the border of the stromal aggregate and spermatogonial cysts appear at the periphery of lamellae. Finally, sex change to secondary males was considered complete, with the beginning of active spermatogenesis and spermiation. Plasma levels of testosterone remained low throughout the sex change, but II-KT increased rapidly parallel to the increased number of Leydig cells while the level of estradiol-17β decreased. The results indicate also that the sex-changed males had higher level of II-KT than primary males, while primary males had higher level of testosterone. Histological examination revealed that testes of primary and secondary males are almost identical in organization of the spermatogenic cysts, association of sertoli cells, and developing germ cells but differ in clustering and development of Leydig cells.     

尼罗罗非鱼卵巢发育过程中性类固醇激素与卵黄蛋白原含量变化及Vtg mRNA 表达特征

通过组织切片、酶联免疫吸附及荧光定量PCR等方法,研究了尼罗罗非鱼(Oreochromis niloticus)卵巢发育过程中性类固醇激素(雌二醇E2、孕酮P)、卵黄蛋白原(Vtg)含量及Vtg mRNA相对表达水平变化规律。结果表明,尼罗罗非鱼性腺指数(GSI)与卵巢成熟发育间呈同步性变化,Ⅴ期达到峰值。血清中E2含量自卵巢Ⅱ期开始显著升高,Ⅳ期达到峰值,Ⅴ期后显著下降;血清P含量自卵巢Ⅱ期开始不断升高,Ⅴ期达到峰值,Ⅵ期显著下降;E2、P分别在卵巢成熟发育前期与后期发挥作用。肝中Vtg含量先升、后降,Ⅳ期达峰值;血清、卵巢中Vtg含量均自Ⅱ期开始增加,Ⅴ期达峰值,Ⅵ期显著降低;不同组织中Vtg含量变化与卵巢成熟发育间存在密切关联。肝中Vtg mRNA表达水平在Ⅲ期达到峰值,Ⅳ期后持续下调;卵巢中Vtg mRNA表达水平相对较低,Ⅴ期达到峰值;初步推测肝、卵巢同是尼罗罗非鱼Vtg合成部位,肝是Vtg合成的主要器官,在卵黄积累阶段最为活跃,而卵巢Vtg合成水平相对较低。     

广东鲂的胚后发育

利用组织学方法,对珠江下游野生广东鲂(Megalobrama terminalis)性腺进行了显微观察和研究,描述了其卵巢、精巢的结构特征以及各类型生殖细胞形态。结果显示,广东鲂属于一次性产卵类型,卵巢发育类型为部分同步型。其卵巢为细线或条状,卵巢发育经历卵原细胞期、单层滤泡细胞期、卵黄泡期、卵黄充满期、成熟期和退化期。卵细胞发生经历3个阶段：卵原细胞、初级卵母细胞和次级卵母细胞;卵巢初级卵母细胞中核仁外排现象出现在第2时相末期至第3时相早期;精巢呈线状或直棒状,精巢为叶状型结构。精细胞发生经历5个阶段：精原细胞、初级精母细胞、次级精母细胞、精子细胞及精子;繁殖季节精子充满于精小叶内,精小囊消失。

     

Gonadal development, aromatase activity and P450 aromatase gene expression during sex inversion of protogynous red-spotted grouper Epinephelus akaara (Temminck and Schlegel) after implantation of the aromatase inhibitor, fadrozole

In the present study, we implanted 2‐year‐old female red‐spotted grouper, Epinephelus akaara, with a non‐steroidal aromatase inhibitor (AI), fadrozole, in the breeding season and examined changes in gonadal histology, serum sex steroids, aromatase activities and P450 aromatase (P450arom) gene expression in gonads after AI implantation. Aromatase inhibitor at doses from 0.1 to 10.0 mg kg^?1 BW induced a sex inversion and completion of spermatogenesis up to the functional male phase, but doses of 1.0 and 10.0 mg kg^?1 BW AI produced more males than 0.1 mg kg^?1 BW AI. Serum estradiol‐17β (E₂) levels decreased, but 11‐ketotestosterone (11‐KT) levels increased significantly in all the AI‐implanted groups, whereas testosterone (T) levels increased significantly only in the 1.0 mg kg^?1 BW AI‐implanted group. Aromatase activities and P450arom gene expression in gonads were inhibited significantly in the AI‐implanted groups, which was in accordance with the decrease in serum E₂ levels. These results suggested the optimal dose of AI to induce sex inversion to be 1.0 mg kg^?1 BW. Furthermore, the sex inversion induced by AI may be attributed to the inhibition of P450arom gene expression and aromatase activity and the resultant decrease in the biosynthesis of endogenous E₂. Meanwhile, the elevated 11‐KT levels were also associated closely with the occurrence of sex inversion in protogynous red‐spotted grouper.     

Environmental and fishing effects on the abundance,size and sex ratio of the blue‐throated wrasse,Notolabrus tetricus,on South Australian coastal reefs

Abstract The blue‐throated wrasse, Notolabrus tetricus (Richardson), is a site‐attached protogynous hermaphroditic species, with a small home range of 1000–2000 m², and the most abundant fish on inshore coastal reefs of South Australia. Long‐term studies over 18–24 years were conducted at an island reserve site and a fished mainland reference site. At the reserve site the retention rate of fish (reduced by mortality + emigration) was directly correlated with female mean size; the female:male sex ratio ranged from 10 to 20:1, consistent with an induction‐inhibition model of sex‐change. At the fished reference site, female mean size declined under intense fishing, and the sex ratio became strongly skewed towards females. Additional spatial surveys over >2000 km of coast showed that: (1) juvenile and adult abundance was variously determined by habitat features, such as substratum‐type, depth, bottom relief, wave exposure and algal canopy cover, and by geographical factors, such as distance off‐shore and within gulfs; and (2) that female mean size and the sex ratio were strongly influenced by recreational fishing, and to a small extent by bottom relief and other factors. The results suggest that female mean size and the sex ratio together can be used as an indicator of recreational fishing intensity at local scales. As populations of sequential hermaphroditic species are sensitive to size‐selective harvesting, management measures should aim to prevent sperm limitation, reproductive failure and skewed sex ratios in this species.     

三斑海马的人工生态养殖

通过构建三斑海马的生态养殖环境、培育天然活体饵料,形成人工生态系统,提高了幼体的成活率。通过施用发酵鸡粪(即把备用的晒干鸡粪,加水发酵使其熟化)50g/m3或尿素10g/m3,5～7d后,投放海马幼体200ind/m3;放苗28d后,栽培菊花江蓠(密度0.5～2kg/m3)作为水质调控、遮光及养殖海马的缠绕物。江蓠的栽培构建了海马天然饵料的培育场所,藻丛中的小型甲类生物密度达450个/100g以上,形成了良好的养殖三斑海马的人工生态环境,经146d的养殖,生态养殖与投饵养殖模式比较,收获的三斑海马成活率和标准体长分别为70.8%、42.5%,11.13cm、10.04cm。     

Characterization of molecular variants of GnRH, induction of spermiation and sex reversal using salmon GnRH-A and domperidone in the protogynous diandric fish, Synbranchus marmoratus Bloch, (Teleostei, Synbranchidae)

This paper studies the molecular variants of gonadotropin-releasing hormone (GnRH) present in the brain of the protogynous swamp eel, Synbranchus marmoratus, and the effects of the administration of salmon GnRH analogue (sGnRH-A) and the dopamine receptor antagonist, domperidone (DOM) on final maturation and gamete release in this species. Evidence for the presence of two GnRH variants, sGnRH and cIIGnRH were obtained by reverse phase high-pressure liquid chromatography (RP-HPLC) and radioimmunoassay with different antisera. The effects of treatment with sGnRH-A+DOM were checked by three ways: oocyte and milt release by stripping, histological analysis of the gonadal tissue, and androgen serum levels at different times throughout the experiment. In males, spermiation was induced after three weeks of treatment. In the female group, sGnRH-A+DOM did not induce ovulation at the end of the experiment. Histological analysis of the gonads from the female group showed evidence of sex reversal. All the treated fish had elevated androgen serum levels from the third week, with respect to control fish. In all cases, serum estradiol levels were undetectable. These results suggest that treatment with sGnRH analog and DOM induce sex reversal in female and spermiation in males. This revised version was published online in July 2006 with corrections to the Cover Date.     

雌雄同体鱼类性别分化及性转变研究进展

在脊椎动物中,鱼类具有多样的性别分化方式,大致可分为雌雄异体、雌雄同体以及单性生殖3类.一般情况下,鱼类性别决定后,性腺可分化为卵巢或精巢,并且在整个生命周期内保持不变.而在雌雄同体鱼类,其性别可以从雌性转变为雄性、雄性转变为雌性或者在雌雄两种性别间进行多次转变.雌雄同体鱼类具有多种性别转变形式,是研究脊椎动物性别决定...     

红鳍东方鲀gsdf基因的克隆及表达模式分析

该研究克隆了大黄鱼（Larimichthys crocea）gsdf （gonadal soma derived factor）和amh （anti-Müllerian hormone）基因的开放阅读框序列并对它们的表达进行分析。大黄鱼gsdf基因cDNA序列开放阅读框长为618 bp,可编码205个氨基酸,含有信号肽和TGF-β结构域。系统进化分析显示,大黄鱼Gsdf与其他鱼类Gsdf聚为一枝,而与TGF-β超家族其他成员分开。Amh基因cDNA序列开放阅读框为1 563 bp,可编码520个氨基酸,含有信号肽、AMH-N区域和TGF-β保守结构域。系统进化分析显示,大黄鱼Amh与舌齿鲈(Dicentrarchus labrax)Amh进化关系最近。荧光定量PCR表达分析显示,gsdf和amh基因主要在大黄鱼性腺表达,在精巢中的表达量显著高于卵巢（P < 0.05）,2个基因都在性腺分化前开始表达,在雄鱼精巢中表达量呈现先升高后下降的趋势,在卵巢的表达量很低。此外,相比于正常雌鱼,gsdf和amh基因在伪雄鱼（遗传性雌鱼）性腺中的表达量显著上调。这些结果表明,gsdf和amh基因在大黄鱼性腺分化过程中起到重要的作用。

     

Survival of rockhopper penguins in times of global climate change

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Risk analysis of non-native three-spot cichlid,Amphilophus trimaculatus, in the River Cauvery (India)

The three-spot cichlid Amphilophus trimaculatus (Günther) is an ornamental fish known to be invasive but has not been assessed for India. The present study confirmed this non-native species’ identity using conventional and molecular methods, as well as its occurrence in the River Cauvery, the first for this species in a lotic environment outside its native range. Gut content analysis indicated a diet of predominantly insects. The river's water quality and habitat were conducive for the species’ growth and reproduction. Using the Aquatic Species Invasiveness Screening Kit, A. trimaculatus was ranked as posing a “high” risk of being invasive in the River Cauvery, with climate match analysis showing 58% similarity with the species’ native range. Vector and pathway analysis found that A. trimaculatus was introduced to India via the aquarium trade, although consignment origin remains unknown, and the most likely means of entry into the river and its tributaries was the species’ escaping from holding facilities. Subsequent dispersal and impact of the species on native fauna are discussed. The study's outcomes demonstrate the importance of using risk analysis protocols to inform management of non-native species in India, with suggestions provided for immediate and long-term measures for the species’ management.     

Biochemical composition of the wild and cultured seahorses, Hippocampus kuda Bleeker and Hippocampus trimaculatus Leach

The biochemical composition of wild and cultured seahorses Hippocampus kuda Bleeker and Hippocampus trimaculatus Leach was analysed in this study. The crude protein contents (% dry weight) of wild seahorses were high: 72.7±2.5% in H. kuda and 78.5±4.2% in H. trimaculatus . The crude lipid contents (% dry weight) of wild and cultured seahorses (1.1±0.1 vs. 1.4±0.2 for H. kuda and 1.2±0.1 vs. 1.2±0.2 for H. trimaculatus ) were low and did not differ significantly ( F _3, 12=1.461, P =0.12). The essential amino acids and flavour-enhancing amino acids in wild seahorses were higher than those in cultured seahorses, although the essential amino acid index in wild and cultured H. kuda and H. trimaculatus were generally low. The total amino acid content decreased with growth in cultured H. trimaculatus ( F _3, 12=14.927, P <0.05). The poly-unsaturated fatty acid (PUFA) contents in wild and cultured H. kuda and H. trimaculatus were 21.69%, 37.72%, 21.39% and 33.89% respectively. The fatty acid content in seahorses first decreased and then increased with growth both in wild and in cultured H. trimaculatus . The PUFA/saturated fatty acid ratio was 1.31 in cultured H. kuda and 0.87 in cultured H. trimaculatus . The trace metal concentrations in the wild seahorses were relatively low. The results presented in this study provide biochemical information necessary for understanding the medicinal value of H. kuda and H. trimaculatus and for elucidating the potential dietary requirements for their culture.