Gonadal development and sex differentiation in the cichlid fishCichlasoma dimerus (Teleostei, perciformes): A light- and electron-microscopic study

Developmental changes in gene expression and gonad morphology during sex differentiation in Atlantic salmon (Salmo salar)

The Atlantic salmon (Salmo salar) is a globally important species for its value in fisheries and aquaculture, and as a research model. In order to characterise aspects of sex differentiation at the morphological and mRNA level in this species, the present study examined developmental changes in gonad morphology and gene expression in males and females between 0 and 79 days post hatch (dph). Morphological differentiation of the ovary (indicated by the formation of germ cell cysts) became apparent from 52 dph. By 79 dph, ovarian phenotype was evident in 100% of genotypic females. Testes remained in an undifferentiated-like state throughout the experiment, containing germ cells dispersed singularly within the gonadal region distal to the mesentery. There were no significant sex-related differences in gonad cross-section size, germ cell number or germ cell diameter during the experiment. The expression of genes involved in teleost sex differentiation (anti-müllerian hormone (amh), cytochrome P450, family 19, subfamily A, polypeptide 1a (cyp19a1a), forkhead box L2a (foxl2a), gonadal soma-derived factor (gsdf), r-spondin 1 (rspo1), sexually dimorphic on the Y chromosome (sdY)), retinoic acid-signalling (aldehyde dehydrogenase 1a2 (aldh1a2), cytochrome P450 family 26 a1 (cyp26a1), cytochrome P450 family 26 b1 (cyp26b1), t-box transcription factor 1 (tbx1a)) and neuroestrogen production (cytochrome P450, family 19, subfamily A, polypeptide 1b (cyp19a1b)) was investigated. Significant sex-related differences were observed only for the expression of amh, cyp19a1a, gsdf and sdY. In males, amh, gsdf and sdY were upregulated from 34, 59 and 44 dph respectively. In females, cyp19a1a was upregulated from 66 dph. Independent of sex, foxl2a expression was highest at 0 dph and had reduced ∼ 47-fold by the time of morphological sex differentiation at 52 dph. This study provides new insights into the timing and sequence of some physiological changes associated with sex differentiation in Atlantic salmon. These findings also reveal that some aspects of the mRNA sex differentiation pathways in Atlantic salmon are unique compared to other teleost fishes, including other salmonids.

Liposome-Encapsulated Rec8 and Dmrt1 Plasmids Induce Red-Spotted Grouper (Epinephelus akaara) Testis Maturation

In fish, the maturity of gonads plays an important role in the development and reproduction of the population, and it also dictates the success of captive breeding. Therefore, finding ways to promote gonadal maturation is an important goal in aquaculture. In this study, we injected recombinant dmrt1 and rec8 overexpression plasmids packaged in liposomes into the immature testis of red-spotted grouper (Epinephelus akaara) and measured the expression of Dmrt1 and Rec8 protein in vivo. Gonadosomatic index (GSI) and gonadal histology analyses showed that the testis developed from the immature to the mature state within 7 days after plasmid injection. Additionally, the spermatozoa concentration and motility in plasmid-injected fish was the same as that of naturally mature fish. These results provided evidence that delivery of dmrt1 and rec8 expression plasmids into the testis via injection induced testis maturation in vivo.

Developmental aspects of the hypothalamic-pituitary network related to reproduction in teleost fish

The hypothalamic-pituitary-gonadal axis is the main system that regulates reproduction in vertebrates through a complex network that involves different neuropeptides, neurotransmitters, and pituitary hormones. Considering that this axis is established early on life, the main goal of the present work is to gather information on its development and the actions of its components during early life stages. This review focuses on fish because their neuroanatomical characteristics make them excellent models to study neuroendocrine systems. The following points are discussed: i) developmental functions of the neuroendocrine components of this network, and ii) developmental disruptions that may impact adult reproduction. The importance of the components of this network and their susceptibility to external/internal signals that can alter their specific early functions and/or even the establishment of the reproductive axis, indicate that more studies are necessary to understand this complex and dynamic network.

Primordial Germ Cell Migration and Histological and Molecular Characterization of Gonadal Differentiation in Pachón Cavefish Astyanax mexicanus

The genetic regulatory network governing vertebrate gonadal differentiation appears less conserved than previously thought. Here, we investigated the gonadal development of Astyanax mexicanus Pachón cavefish by looking at primordial germ cells (PGCs) migration and proliferation, gonad histology, and gene expression patterns. We showed that PGCs are first detected at the 80% epiboly stage and then reach the gonadal primordium at 1 day post-fertilization (dpf). However, in contrast to the generally described absence of PGCs proliferation during their migration phase, PGCs number in cavefish doubles between early neurula and 8-9 somites stages. Combining both gonadal histology and vasa (germ cell marker) expression patterns, we observed that ovarian and testicular differentiation occurs around 65 dpf in females and 90 dpf in males, respectively, with an important inter-individual variability. The expression patterns of dmrt1, gsdf, and amh revealed a conserved predominant male expression during cavefish gonadal development, but none of the ovarian differentiation genes, i. e., foxl2a, cyp19a1a, and wnt4b displayed an early sexually dimorphic expression, and surprisingly all these genes exhibited predominant expression in adult testes. Altogether, our results lay the foundation for further research on sex determination and differentiation in A. mexicanus and contribute to the emerging picture that the vertebrate sex differentiation downstream regulatory network is less conserved than previously thought, at least in teleost fishes.

Morphological characterization of pirarucu Arapaima gigas (Schinz, 1822) gonadal differentiation

Arapaima gigas is a giant air-breathing and bony tongue fish from the Amazon basin and a promising species for aquaculture. A. gigas farming industry is still not established because of the lack of information on its reproductive physiology. Reproduction in captivity cannot be manipulated or stimulated, and the identification of males and females in a broodstock is not easy. We aimed to reveal the morphological sex differentiation of pirarucu as studies involving gonad development are essential to understanding the reproductive physiology of any species. We performed histological analysis on the whole body and extracted the gonads of 150 juveniles. The first sign of ovary differentiation is the sex-specific rearrangement of the germ cells. In 9 cm total length females, the germ cells group into nests and are restricted to the lateral face of the gonad, in close contact with the abdomen wall. With further development, this region invaginates and that later develops into ovigerous lamellae. Meiosis starts soon after ovary differentiation. In males, the germ cells are scattered along the elongated differentiating testis at first, and later become more restricted to the central region where the spermatogonial cysts start to develop. Somatic and germ cells are jointly involved in the cellular reorganization during gonadal differentiation, specifically when the germ cells begin to establish new associations during the development of both the germinal epithelium and stroma. RESEARCH HIGHLIGHTS: In Arapaima gigas, the ovary differentiation occurs in 9 cm TL females and it is marked by the rearrangement of germ and somatic cells; and the germ cells entering meiosis with no formation of ovarian cavity; testis differentiation occurs later and meiosis does not start in males smaller than 80 cm TL.

Transcriptome of tambaqui Colossoma macropomum during gonad differentiation: Different molecular signals leading to sex identity

Tambaqui (Colossoma macropomum) is the major native species in Brazilian aquaculture, and we have shown that females exhibit a higher growth compared to males, opening up the possibility for the production of all-female population. To date, there is no information on the sex determination and differentiation molecular mechanisms of tambaqui. In the present study, transcriptome sequencing of juvenile trunks was performed to understand the molecular network involved in the gonadal sex differentiation. The results showed that before differentiation, components of the Wnt/β-catenin pathway, fox and fst genes imprint female sex development, whereas antagonistic pathways (gsk3b, wt1 and fgfr2), sox9 and genes for androgen synthesis indicate male differentiation. Hence, in undifferentiated tambaqui, the Wnt/β-catenin exerts a role on sex differentiation, either upregulated in female-like individuals, or antagonized in male-like individuals.

Testis structure, spermatogonial niche and Sertoli cell efficiency in Neotropical fish

Neotropical icthyofauna represents one of the most diverse and extreme ecosystems in the world. Likewise, reproduction showed enormous diversity with different reproductive systems, modes and behavior. On the other hand, information on Neotropical fish species, in particular on male reproductive physiology is restricted to few species. This mini-review aimed to compile the existing information on spermatogenesis of Neotropical teleosts focusing on testis structure, spermatogonial niche and Sertoli cell efficiency. The first topic covers the histological analysis of the testicular structure, showing a conserved testicular pattern in relation to the phylogenetic position: basal species present anastomosing tubular testis (e.g. Astyanax altiparanae, Conorhynchos conirostris, Pimelodus maculatus, Lophiosilurus alexandri, Rhinelepis aspera, among others), while derived teleosts showed lobular testis (e.g. Cichlasoma dimerus, Cichla kelberi, Odontesthes bonariensis, Synbranchus marmoratus and others). Next to testicular structure, existing data showed that type A undifferentiated spermatogonia (A_und) is differentially distributed among the Neotropical species. A_und can be restricted at the blind-end of the germinal compartment (O. bonariensis), or spread along the germinal epithelium (A. altiparanae), or even distributed along the germinal epithelium but concentrated at the blind-end (C. kelberi and C. intermedia). Moreover, recent studies in A. altiparanae have demonstrated that within the germinal compartment, A_und have a preferential distribution in areas neighboring the interstitial compartment - the spermatogonial niche. The proximity with the interstitium suggests that interstitial cells, such as Leydig cells, are important for A_und maintenance in the testis. Finally, this mini-review highlighted Sertoli cell efficiency, showing that a single Sertoli cell can support a higher number of germ cells (80-140 spermatids) in Neotropical species evaluated at the moment (e.g. A. altiparanae, Hoplias malabaricus, Poecilia reticulata, Serrasalmus spilopleura, C. intermedia). Overall, this review provided basic and functional information on spermatogenesis of Neotropical species. More studies in this field are necessary since Neotropical region is considered one of the hotspot regions to discovery new species providing, therefore, new opportunities to investigate spermatogenesis in fish.

Ontogeny of Gonadotropin-Inhibitory Hormone (GnIH) in the cichlid fish Cichlasoma dimerus

RFamide peptides are expressed in the early stages of development in most vertebrates. Gonadotropin-inhibitory hormone (GnIH) belongs to the RFamide family, and its role in reproduction has been widely studied in adult vertebrates, ranging from fish to mammals. As only three reports evaluated GnIH during development, the aim of this study was to characterise the ontogeny of GnIH in a fish model, Cichlasoma dimerus. We detected the presence of two GnIH-immunoreactive (GnIH-ir) cell clusters with spatial and temporal differences. One cluster was observed by 3 days post-hatching (dph) in the nucleus olfacto-retinalis (NOR) and the other in the nucleus posterioris periventricularis by 14 dph. The number of GnIH-ir neurons increased in both nuclei, whereas their size increased only in the NOR from hatchling to juvenile stages. These changes occurred from the moment larvae started feeding exogenously and during development and differentiation of gonadal primordia. We showed by double-label immunofluorescence that only GnIH-ir neurons in the NOR co-expressed GnRH3 associated peptide. In addition, GnIH-ir fibre density increased in all brain regions from 5 dph. GnIH-ir fibres were also detected in the retina, optic tract and optic tectum, suggesting that GnIH acts as a neuromodulator of photoreception and the integration of different sensory modalities. Also, there were GnIH-ir fibres in the pituitary from 14 dph, which were in close association with somatotropes. Moreover, GnIH-ir fibres were observed in the saccus vasculosus from 30 dph, suggesting a potential role of GnIH in the modulation of its function. Finally, we found that gnih was expressed from 1 dph, and that the pattern of variation of its transcript levels was in accordance with that of cell number. Present results are the starting point for the study of new GnIH roles during development. This article is protected by copyright. All rights reserved.

Action of the Metalloproteinases in Gonadal Remodeling during Sex Reversal in the Sequential Hermaphroditism of the Teleostei Fish Synbranchus marmoratus (Synbranchiformes: Synbranchidae)

Teleostei present great plasticity regarding sex change. During sex reversal, the whole gonad including the germinal epithelium undergoes significant changes, remodeling, and neoformation. However, there is no information on the changes that occur within the interstitial compartment. Considering the lack of information, especially on the role played by metalloproteinases (MMPs) in fish gonadal remodeling, the aim of this study was to evaluate the action of MMPs on gonads of sex reversed females of Synbranchus marmoratus, a fresh water protogynic diandric fish. Gonads were processed for light microscopy and blood samples were used for the determination of plasma sex steroid levels. During sex reversal, degeneration of the ovaries occurred and were gradually replaced by the germinal tissue of the male. The action of the MMPs induces significant changes in the interstitial compartment, allowing the reorganization of germinal epithelium. Leydig cells also showed an important role in female to male reversion. The gonadal transition coincides with changes in circulating sex steroid levels throughout sex reversion. The action of the MMPs, in the gonadal remodeling, especially on the basement membrane, is essential for the establishment of a new functional germinal epithelium.

Gonadal morphogenesis and sex differentiation in cultured Ussuri catfish Tachysurus ussuriensis

The objective of this study was to investigate the optimal developmental time to perform sex reversal in Ussuri catfish Tachysurus ussuriensis, to develop monosex breeding in aquaculture. Systematic observations of gonadal sex differentiation of P. ussiriensis were conducted. The genital ridge formed at 9 days post fertilization (dpf) and germ cells begin to proliferate at 17 dpf. The ovarian cavity began forming on 21 dpf and completed by 25 dpf while presumptive testis remained quiescent. The primary oocytes were at the chromatin nucleolus stage by 30 dpf, the peri-nucleolus stage by 44 dpf and the cortical alveoli stage by 64 dpf. The germinal vesicle migrated towards the animal pole (polarization) at 120 dpf. In presumptive testis, germ cells entered into mitosis and blood vessels appeared in the proximal gonad on 30 dpf. The efferent duct anlage appeared on 36 dpf and formation of seminal lobules with spermatogonia and lobules interstitium occurred at 120 dpf. Therefore, gonadal sex differentiation occurred earlier in females than in males, with the histological differentiation preceding cytologic differentiation in T. ussuriensis. This indicates that undifferentiated gonads directly differentiate into ovary or testis between 17 and 21 dpf and artificial induction of sexual reversal by oral steroid administration must be conducted before 17 dpf.

Ovarian differentiation and development in cachara Pseudoplatystoma fasciatum

One thousand five hundred cachara or tiger shovelnose catfish Pseudoplatystoma fasciatum, obtained from induced reproduction, were used to determine the onset of ovarian differentiation and development and to record the main characteristics of this process. Samples were collected from 0 to 240 days post-fertilization (dpf) and the results classified into stages I-XII. Ovarian formation was histologically detected for the first time when juveniles measured mean ± s.d. 51·5 ± 8·3 mm total length (LT ) at 39-45 dpf (stages I-V), with intense somatic cell proliferation originating in the ovarian cavity. Both LT and age of fish had a positive correlation (P < 0·001) with ovarian differentiation, but LT showed a greater correlation (r(2)  = 0·95) than age (r(2)  = 0·85), especially during the initial stages of development. From stages VI to VII, the ovarian cavity was enlarged and undifferentiated oogonia were present. At stage VIII, small projections formed in the ovarian stroma towards the ventral region of the gonad (future ovarian lamellae) and the basal membrane and differentiated oogonia nests could be seen. At stages IX and X, the germ cells entered meiosis and folliculogenesis was completed by stages XI and XII, which can be considered late in comparison to other Siluriformes. This study has demonstrated that ovarian differentiation in P. fasciatum begins with an intense proliferation of squamous epithelial cells (somatic cells) during the early stages of development and that sex inversion protocols could, thus, be applied successfully before this period. Furthermore, the results have demonstrated that both size and age can influence gonad differentiation and development in this species.

Effects of waterborne exposure to 17β-estradiol and 4-tert-octylphenol on early life stages of the South American cichlid fish Cichlasoma dimerus

Estrogenic chemicals are often detected in the aquatic environment and can negatively affect animal development and reproduction. In teleost fishes, the hormonal regulation during a critical period of larval development has a strong influence on gonadal sex differentiation; thus this process may be affected by the exposure to environmental estrogens. In this study, we first assessed the lethal acute toxicity of the natural estrogen 17β-estradiol (E2) and the weaker estrogen mimics 4-tert-octylphenol (OP) and 4-nonylphenol (NP) on larval stages of the South American cichlid fish Cichlasoma dimerus. In a further experiment, we analyzed the effects of chronic waterborne exposure to E2 and OP on gonad development and sex differentiation. Exposure to high concentrations of E2 had a pronounced feminizing effect directing sex differentiation towards ovarian development, while testis development was inhibited at a lower, environmentally relevant concentration. Among OP-exposed fish, 15-38.5% of the males exhibited testicular oocytes (TOs), a commonly reported biomarker of estrogenic exposure. However, since TOs were also recorded in control males and the proportion of males with TOs was not significantly higher in OP treatments, their occurrence could not be attributed to OP exposure. In addition, TOs did not seem to impair male gonad development and functionality since normal spermatogenesis was observed in testes of OP-treated fish. These results indicate that E2 occurring in the South American aquatic environment may affect male reproductive development and pose a risk for wild C. dimerus, especially under prolonged exposure, while the effects of weaker xenoestrogens such as OP would be negligible for gonad development in this species. As illustrated by this study, the natural occurrence of TOs indicates that conclusions concerning the causes of this phenomenon must be drawn with care.

Reproductive hormones affect follicular cells and ooplasm of Stage I and II oocytes in zebrafish

The basic pathway of oocyte development and its regulation is evolutionarily conserved among vertebrates; however, little is known about the role of hormones at the first stages (Stages I and II) of follicle development in fish. In the present study, zebrafish follicles at Stages I and II were exposed in vitro to the reproductive hormones 17β-oestradiol (E2), 11-ketotestosterone (11KT), 17,20β-dihydroxy-4-pregnen-3-one (DHP) and to the secondary messenger dibutyryl cyclic adenosine monophosphate (db-cAMP) at a concentration of 1 µM for a 48-h period. Morphological alterations of the ooplasm were assessed by transmission electron microscopy and of the granulosa cell layer by quantitative stereology. Expression of mRNA was analysed for cell-cycle genes (cyclin B and E) and resident proteins of the endoplasmic reticulum (calnexin and 78-kDa glucose-regulated protein (grp78/bip)). E2 and db-cAMP stimulated the presence of endoplasmic reticulum in the ooplasm and calnexin mRNA increased in the db-cAMP treatment, but also in response to 11KT and DHP. 11KT, DHP and db-cAMP inhibited the progression of the cell cycle in the granulosa–theca cell layer, indicated by a reduction of the nucleus volume-weighted size of granulosa cells and of increased cyclin E mRNA expression. Reproductive hormones had different effects on the ooplasm and the granulosa–theca cell layer of zebrafish follicles, predominantly at Stage II.

Molecular identification and expression of the Foxl2 gene during gonadal sex differentiation in northern snakehead Channa argus

Channa argus is one of the most commercially important fish species in China. Studies show that males of C. argus grow faster than females at the same age. In order to explore the sex differentiation mechanism of C. argus, we isolated the full length of the sex-related gene Foxl2 cDNA and analysed its expression patterns during gonadal sex differentiation. Alignment of known Foxl2 amino acid sequences from vertebrates confirmed the conservation of the Foxl2 open reading frame, especially the forkhead domain and C-terminal region. Quantitative RT-PCR revealed that Foxl2 is predominantly expressed in brain, pituitary, gill and ovary, with its highest level in ovary but low levels in testis and other tissues, reflecting a potential role for Foxl2 in the brain-pituitary-gonad axis in C. argus. Our ontogenetic stage data showed that C. argus Foxl2 expression was significantly upregulated from 1 to 11 days posthatching (dph) and that the initiation of expression preceded the first anatomical ovarian differentiation (27 dph), suggesting that Foxl2 might play a potential role in early gonadal sex differentiation in C. argus. In addition, the Foxl2 protein was primarily located in granulosa cells surrounding the oocytes of mature C. argus, implying that Foxl2 may have a basic function in granulosa cell differentiation and the maintenance of oocytes.

The basement membrane and the sex establishment in the juvenile hermaphroditism during gonadal differentiation of the Gymnocorymbus ternetzi (Teleostei: Characiformes: Characidae)

Although there are several studies on morphogenesis in Teleostei, until now there is no research describing the role of the basement membrane in the establishment of the germinal epithelium during gonadal differentiation in Characiformes. In attempt to study these events that result in the formation of ovarian and testicular structures, gonads of Gymnocorymbus ternetzi were prepared for light microscopy. During gonadal development in G. ternetzi, all individuals first developed ovarian tissue. The undifferentiated gonad was formed by somatic cells (SC) and primordial germ cells (PGCs). After successive mitosis, the PGCs became oogonia, which entered into meiosis originating oocytes. An interstitial tissue developed. In half of the individuals, presumptive female, prefollicle cells synthesized a basement membrane around oocyte forming a follicle. Along the ventral region of the ovary, the tissue invaginated to form the ovigerous lamellae, bordered by the germinal epithelium. Stroma developed and the follicle complexes were formed. The gonadal aromatase was detected in interstitial cells in the early steps of the gonadal differentiation in both sexes. In another half of the individuals, presumptive male, there was no synthesis of basement membrane. The interstitium was invaded by numerous granulocytes. Pre-Leydig cells proliferated. Apoptotic oocytes were observed and afterward degenerated. Spermatogonia appeared near the degenerating oocytes and associated to SCs, forming testicular tubules. Germinal epithelium developed and the basement membrane was synthesized. Concomitantly, there was decrease of the gonadal aromatase and increase in the 3β-HSD enzyme expression. Thus, the testis was organized on an ovary previously developed, constituting an indirect gonochoristic differentiation.

Morphological and molecular effects of cortisol and ACTH on zebrafish stage I and II follicles

Oogenesis in zebrafish (Danio rerio) is controlled by the hypothalamus-pituitary-gonadal axis and reproductive hormones. In addition, an interference of stress hormones is known with reproductive biology. In the presented work, we aimed to explore the hypothesis that cortisol (Cort) and ACTH may affect early oogenesis in zebrafish, given the presence of the specific receptors for glucocorticoids and ACTH in the zebrafish ovary. Follicles at stages I and II were exposed in vitro to 1  μM Cort and ACTH for 48 h, then ultrastructural and molecular effects were analyzed. The comet assay demonstrated increased tail moments for Cort and ACTH treatment indicative of DNA damage. The mRNA expression of apoptotic genes (bax, bcl-2) was not altered by both treatments, but Cort increased significantly the expression of the ACTH receptor (mc2r). Cort stimulated the presence of the endoplasmic reticulum, predominantly at stage II, while ACTH induced a strong vacuolization. Viability of oocytes was not affected by both treatments and fluorescent staining (monodansylcadaverine/acridine orange) indicated a reduced quantity of autophagosomes for ACTH, and lower presence of nucleic acids in ooplasm for Cort and ACTH. Concluding, different responses were observed for stress hormones on early stages of zebrafish oocytes, which suggest a role for both hormones in the stress-mediated adverse effects on female gametogenesis.

Endosulfan affects GnRH cells in sexually differentiated juveniles of the perciform Cichlasoma dimerus

Endosulfan (ES) is an organochlorine pesticide widely used in agriculture despite its high toxicity towards non-target organisms such as fish. It has been demonstrated that ES can cause negative effects on aquatic animals, including disruption of hormonal systems. However, the alterations produced by this pesticide on the reproductive axis of fish prior to sexual maturity, as well as possible modes of action have hardly been studied. This study aimed at assessing the effect of waterborne exposure to the pesticide ES on the reproductive axis during sexual differentiation of juveniles of the South American freshwater cichlid fish Cichlasoma dimerus. No mortality was observed due to ES subchronic exposure (90 days post-fertilization). Exposure to ES did not affect body weight nor morphometric parameters, indicating that larvae nutritional state was not affected. Timing of sexual differentiation, gonadal morphology and sex ratio were likewise not altered by ES. However, ES acted as an endocrine disrupting chemical in this species as the morphometry of gonadotropin-releasing hormones (GnRH) producing cells was altered. Exposure to ES altered nuclear area, cell area and nucleus/cytoplasm ratio of GnRH II neurons, and cell and nuclear area and diameter of GnRH III neurons. Interestingly, in our previous study, exposure before sex differentiation (30 day exposure) caused no alteration to GnRH II and III, and did alter GnRH I and FSH cells. These alterations could lead to changes in circulating hormone levels, especially when fish are exposed for prolonged periods, ultimately impairing reproductive fitness. C. dimerus juveniles can be an interesting biological model to perform toxicological studies with the intent to assess early disruption endpoints in the reproductive axis during development.

Differentiation and morphogenesis of the ovary and expression of gonadal development-related genes in the protogynous hermaphroditic ricefield eel Monopterus albus

The ovarian differentiation, morphogenesis and expression of some putative gonadal development-related genes were analysed in the ricefield eel Monopterus albus, a protogynous hermaphroditic teleost with a single elongate ovary. At c. 1 day post-hatching (dph), the gonadal ridge was colonized with primordial germ cells (PGCs) at the periphery and transformed into the gonadal primordium, which appeared to contain two germinal epithelia. At c. 7 dph, four ovarian cavities appeared in the gonadal tissue with two in each germinal epithelial compartment, and the indifferent gonad might have begun to differentiate into the ovary. The oocytes at the leptotene stage in meiosis I appeared at c. 14 dph, and oocytes at the diplotene stage at c. 30 dph. As development proceeded, the connective tissue separating the two germinal epithelia disappeared, and two of the four ovarian cavities collapsed into one. At 60 dph, the gonad had already taken the shape as observed in the adults. One outer and two inner ovarian cavities could be easily recognized, with slightly basophilic primary growth oocytes usually residing close to the outer ovarian cavity. The expression of cyp19a1a and erb in the early gonad was detected at 6 dph. The abundant expression of foxl2 coincided with the up-regulation of cyp19a1a at 8 dph onwards. The expression of dmrt1 isoforms was not detectable until 8 dph for dmrt1a and dmrt1b and until 33 dph for dmrt1d. The earlier appearance of cyp19a1a compared to dmrt1 transcripts in the indifferent gonad may contribute to the initial differentiation of the gonad towards the ovary in M. albus.

Male gonadal differentiation and the paedomorphic evolution of the testis in Teleostei

Testis differentiation from representatives of the Otophysi (Cyprinus carpio), Percomorpha (Amatitlania nigrofasciata), and Atherinomorpha (Poecilia reticulata) was comparatively described. In the undifferentiated gonad of C. carpio, the primordial germ cells (PGCs) are scattered throughout the gonads while in A. nigrofasciata and P. reticulata the PGCs are restricted to the ventral periphery. In the dorsal region of the developing gonads, with the exception of C. carpio, somatic cell rearrangements result in the differentiation of the sperm duct. Pre-Sertoli cells wrap around single spermatogonia forming cysts that proliferate forming acinar-clusters. In C. carpio and A. nigrofasciata, the cysts in each acinar-cluster move away from each other, creating a central lumen. In C. carpio, the acinar-clusters then fuse to each other forming tubules that become lined by the germinal epithelium. Subsequently, the tubules anastomose dorsally and create the sperm duct. In A. nigrofasciata, the acinar-clusters elongate, forming lobules that individually connect to the sperm duct. These are lined by the germinal epithelium. In P. reticulata, the spermatogonial cysts remain in the acinar-cluster organization. Subsequently, developing ducts connect each cluster to the sperm duct and lobules subsequently develop. In the differentiated testis of C. carpio and A. nigrofasciata, spermatogonia are distributed along the lengths of the anastomosing tubules or lobules, respectively. However, in P. reticulata, the spermatogonia remain restricted to the terminal end of the lobules. Considering testis ontogeny, the spermatogonial acinar-cluster is the adult characteristic of more derived taxa that approximate the early gonad developmental stages of the basal taxa.

Histopathological changes in Poecilia latipinna male gonad due to Tribulus terrestris administration

Tribulus terrestris is a traditionally known non-toxic aphrodisiac herb for maleness. It was experimented recently to understand the effect and mechanism on mono sex production in Poecilia latipinna. It would help to develop a new eco-friendly way to masculinize P. latipinna, since males have higher commercial value than females. The different concentration (100, 150, 200, 250 and 300 mg/L) of T. terrestris extract and a control were tested for their effect on sex transformation/reversal in P. latipinna by immersing the newly born young ones in the respective concentrations for 2 mo. The obtained results indicate that a dose dependant masculinization is obtained due to T. terrestris administration, which improved the male proportion. Histological results revealed that the testes of fish treated with T. terrestris extract contained all stages of spermatogenesis, clearly demonstrating that the administration of T. terrestris extract to P. latipinna stimulated spermatogenesis. Thus, it is discernible that 0-d-old hatchlings of P. latipinna exposed to T. terrestris extract orient/reverse their sex more towards maleness besides yielding better growth and spermatogenesis which is a mandate for fancy fish industry.

Gonadal morphogenesis and sex differentiation in the viviparous fish Chapalichthys encaustus (Teleostei, Cyprinodontiformes, Goodeidae)

This study describes the structural and ultrastructural characteristics of gonadal sex differentiation and expression of Vasa, a germline marker, in different developmental stages of embryos and newborn fry of the barred splitfin Chapalichthys encaustus, a viviparous freshwater teleost endemic to Mexico. In stage 2 embryos, the gonadal crest was established; gonadal primordia were located on the coelomic epithelium, formed by scarce germ and somatic cells. At stage 3, the undifferentiated gonad appeared suspended from the mesentery of the developing swimbladder and contained a larger number of germ and somatic cells. At stages 4 and 5, the gonads had groups of meiotic and non-meiotic germ cells surrounded by somatic cells; meiosis was evident from the presence of synaptonemal complexes. These stages constituted a transition towards differentiation. At stage 6 and at birth, the gonad was morphologically differentiated into an ovary or a testis. Ovarian differentiation was revealed by the presence of follicles containing meiotic oocytes, and testicular differentiation by the development of testicular lobules containing spermatogonia in mitotic arrest, surrounded by Sertoli cells. Nuage, electron-dense material associated with mitochondria, was observed in germ cells at all gonadal stages. The Vasa protein was detected in all of the previously described stages within the germ-cell cytoplasm. This is the first report on morphological characteristics and expression of the Vasa gene during sexual differentiation in viviparous species of the Goodeidae family. Chapalichthys encaustus may serve as a model to study processes of sexual differentiation in viviparous fishes and teleosts.

Diet and food consumption of the pearl cichlid Geophagus brasiliensis (Teleostei: Cichlidae): relationships with gender and sexual maturity

Despite the importance of the pearl cichlid Geophagus brasiliensis for the aquarium fish trade worldwide and its wide distribution, many aspects of its biology, such as the relationships between its feeding ecology and reproductive behavior, are not fully understood in natural conditions on its native habitat. In this paper, we investigated its diet focusing on how differences in diet and food consumption are related to differences in gender and sexual maturity. The digestive tract of each individual was dissected and had its content analyzed, whereas each gonad was microscopically analyzed to determine gender (male/female) and sexual maturity (immature/mature). A total of 28 females and 31 males were analyzed. Mature individuals were more common than immature specimens both for males (64.50%) and females (64.30%). The analysis of 52 individuals with non-empty digestive tracts revealed a diet comprised of 27 items. According to the Index of Alimentary importance (%IAi), the most important food items in the diet were Gastropoda (37.30%), fragments of vascular plants (15.16%), detritus (10.14%), Amphipoda (9.24%), and fish scales (6.29%). Mature males had more empty stomachs (65.00%) when compared to immature males (27.27%) and immature (55.56%) and mature females (40.00%). Also, mature females seemed to have more food consumption (greater mean values of total volume) in their digestive tracts than mature males. Some hypotheses are proposed in order to distinguish if this gender-based difference in food consumption in mature individuals of the pearl cichlid could be associated with the development of primary and secondary sexual characteristics or with asymmetrical time invested in parental care activities.

Effect of the organochlorine pesticide endosulfan on GnRH and gonadotrope cell populations in fish larvae

Endocrine-disrupting chemicals can influence the hypothalamus-pituitary-gonad axis and possibly affect reproduction in vertebrates. We analyzed the effect of 30-day endosulfan (ES) exposure in sexually undifferentiated larvae of the cichlid fish Cichlasoma dimerus. The number, area, mean cytoplasmic and nuclear diameter, and mean cytoplasmic optical density of gonadotropin-releasing hormone (GnRH) I, II, and III immunoreactive (ir-) neurons and β follicle-stimulating hormone (βFSH) ir-cells were measured. Animals exposed to the highest ES concentration (0.1 μg/l) showed a decrease in GnRH I nucleus/cytoplasm area ratio upon exposure. Nuclear area and mean nuclear diameter of βFSH ir-cells was higher in ES treated fish. βFSH nucleus/cytoplasm area ratio was high in exposed animals, and animals exposed to 0.1 μg/l ES showed smaller mean cytoplasmic optical density. These findings suggest that ES affects GnRH I and βFSH protein synthesis/release. However, these responses seem to be insufficient to affect gonadal differentiation at this stage of development.

Gonad plasticity and gametogenesis in the endangered Spanish toothcarp Aphanius iberus (Teleostei: Cyprinodontidae)

The Spanish toothcarp Aphanius iberus is an endangered species which inhabits small rivers, creeks, salt marshes and marine salt pans in the Mediterranean coast of Spain. No differences in weights were observed among females or males taken from different environments. Analyses of the morphology of the gonads and the gametogenesis were performed in fish taken from different environments by comparing gamete development in females and in males and gonadal cell proliferation in the testis. A high degree of plasticity was observed in the gonad morphology of A. iberus. Females possess two ovaries which show non-restricted oogenesis with all germ cell stages within the same ovigerous lamellae, while males possess gonads without any clear division with the typical restricted pattern observed in cyprinodontid fish. Some females and males showed asymetrically developed gonads. Proliferation of germ cells in testis is located only in the periphery of the gonads corresponding with primary and secondary spermatogonia. Salinity did not influence gonad plasticity or the appearance of mature germ cells in either females or males. This is the first study to provide a microscopic description of oogenesis and spermatogenesis in A. iberus at extreme different environmental conditions.

Temporal expression of two cytochrome P450 aromatase isoforms during development in Oreochromis mossambicus, in association with histological development

Oreochromis mossambicus is targeted as a sentinel species for assay development to detect disruption of estrogen-dependent pathways in Southern Africa. Aromatase--an enzyme encoded by either of two cytochrome P450 19 (cyp19) genes in O. mossambicus is the only enzyme able to catalyze the aromatization of androgens to estrogens. As part of background studies relating to evaluating the use of early life stages of O. mossambicus as an endocrine disruptor screen, we investigated the tissue specificity and temporal expression of cyp19 transcripts, cyp19a (ovarian cyp19) and cyp19b (brain cyp19) during development and estrogen exposure. The cyp19a transcript was detected only in the ovaries of adults, and expression during development reflected this result as induction of cyp19a coincides with histological development of putative ovaries. Using primers that only identify the ovarian transcript, cyp19a transcript levels demonstrated a typical reflection of puberty - after an initial surge in cyp19a, juveniles expressed very low levels, which increased again at the time histologically discernable vitellogenic ovaries were detected. Moreover, we found evidence of putative alternate transcript of cyp19a whose function is currently unknown. cyp19b transcripts were expressed in brain and muscle tissue of both male and female adults, in addition to ovaries in females. During development, cyp19b transcript levels were increased coincidental with cyp19a at 20 days post fertilization but the expression pattern was distinct from that observed for cyp19a. These studies set the foundation for utilizing this native species as a possible indicator of endocrine disruption and accentuates the importance of understanding "normal" basal levels of transcript levels and the nature of amplification of QPCR targets.

Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout,Oncorhynchus mykiss(Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)

The rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a salmoniform fish that spawns once per year. Ripe females that had ovulated naturally, and those induced to ovulate using salmon gonadotropin-releasing hormone, were studied to determine whether follicles were forming at the time of spawning and to describe the process of folliculogenesis. After ovulation, the ovaries of postspawned rainbow trout were examined histologically, using the periodic acid-Schiff procedure, to stain basement membranes that subtend the germinal epithelium and to interpret and define the activity of the germinal epithelium. After spawning, the ovary contained a few ripe oocytes that did not ovulate, numerous primary growth oocytes including oocytes with cortical alveoli, and postovulatory follicles. The germinal epithelium was active in postspawned rainbow trout, as determined by the presence of numerous cell nests, composed of oogonia, mitotic oogonia, early diplotene oocytes, and prefollicle cells. Cell nests were separated from the stroma by a basement membrane continuous with that subtending the germinal epithelium. Furthermore, follicles containing primary growth oocytes were connected to the germinal epithelium; the basement membrane surrounding the follicle joined that of the germinal epithelium. After ovulation, the basement membrane of the postovulatory follicle was continuous with that of the germinal epithelium. We observed consistent separation of the follicle, composed of an oocyte and surrounding follicle cells, from the ovarian stroma by a basement membrane. The follicle is derived from the germinal epithelium. As with the germinal epithelium, follicle cells derived from it never contact those of the connective tissue stroma. As with epithelia, they are always separated from connective tissue by a basement membrane.

Identification of immunoreactive FSH and LH cells in the cichlid fish Cichlasoma dimerus during the ontogeny and sexual differentiation

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) expressing cells were detected in pituitary, brain and ovary of the Perciform cichlid fish Cichlasoma dimerus. This detection was carried out by immunohistochemistry (IHC) and Western blot techniques using antisera of the Cyprinodontiform Fundulus heteroclitus raised against the conservative region of the teleost betaFSH and the betaLH subunits. The estimated molecular weights were 24 kDa for LH and 19 and 15 kDa for FSH. In the adult pituitary, both cell types were distributed along mid and ventral zones of the proximal pars distalis (PPD, mid-immunoreactive cells), and along the ventral and dorsal external border of the pars intermedia (PI, high-immunoreactive cells). Double IHC showed that FSH and LH are mainly expressed in different pituitary cells. FSH cells were detected in the pituitary around day 21 after hatching (ah) (prior to sex differentiation), while LH cells were detected by day 60 ah (during the sexual differentiation period). A correlation between gonadal sex differentiation and FSH was demonstrated in a 15 days organ culture system. FSH and LH neurons were localized in the nucleus lateralis tuberis and their fibers project through the ventral hypothalamus, preoptic area and neurohypophysis. FSH neurons differentiated on day 21 ah, while LH neurons appeared on day 15 ah. In the ovary, the immunoreactivity for both FSH and LH was restricted to the cytoplasm of previtellogenic and early vitellogenic oocytes.

Testis structure, spermatogenesis, spermatocytogenesis, and sperm structure in cardinal fish (Apogonidae, Perciformes)

The testes in all 16 of the studied cardinal fish species are shown to be bilobed, with spermatogonia dispersed throughout the gametogenic epithelium of the seminiferous tubules. Each testicular lobe is covered luminally by an epithelium consisting of primary germ cells and Sertoli cells. At maturation the seminiferous tubules reach around 0.6-2.3 mm in length. They number from 60 in the smallest species to over 300 in the largest one, increasing both in dimension and number with increase in length of the male, and are species-specific. The highest number of spermatogonia is found at the apical ends of the tubules. During maturation extensions of Sertoli cells surround single or small groups of B-spermatogonia, forming the spermatocysts, the final dimensions of which reflect the final number of contained spermatozoids. Back-calculations of serial sections reveal that within the spermatocysts the spermatogonia undergo eight generations of mitotic divisions before the first and second meiotic divisions and formation of spermatids. The largest mature spermatocysts in large species attain around 180 microm in diameter, a volume of 25 mm(3), and contain around 8,200 spermatids. The total volume of sperm in the mature spermatocysts leaves enough space for the discarded cytoplasm and developing flagella. The bursting cysts liberate the ripe sperm and maturing spermatids, into the tubule lumen and spermduct, with the spermatids often still connected by cytoplasm bridges. The sperm, with one or two flagella, features round or oval heads and a cytoplasmic collar bearing a few mitochondria. The percentage of biflagellate or monoflagellate sperm differs in proportion in males of different lengths and in different species. Differences in spermatogenesis of small and larger species of cardinal fish are discussed.

Cytochemical characterization of the endomembranous system during the oocyte primary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

The morphophysiological changes that occur during oocyte primary growth in Serrasalmus spilopleura were studied using ultrastructural cytochemical techniques. In the previtellogenic oocytes endoplasmic reticulum components, Golgi complex cisternae and vesicles, lysosomes, multivesicular bodies and some electron-dense vesicles react to acid phosphatase (AcPase) detection. The endoplasmic reticulum components, Golgi complex cisternae and vesicles also react to osmium tetroxide and potassium iodide impregnation (KI). These structures, except for the Golgi complex cisternae, are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). Some electron-dense vesicles are ZIO-stained, while microvesicles in the multivesicular bodies and other large isolated cytoplasmic vesicles are contrasted by KI. At primary oocyte growth, the activity of the endomembranous system and the proliferation of membranous organelles are intense. The biosynthetic pathway of the lysosomal proteins such as acid phosphatase, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes and, finally, the lysosomes. The oocyte endomembranous system have reduction capacity and are involved in the metabolism of rich in SH groups.