Annual changes in germinal epithelium determine male reproductive classes of the cobia

Five reproductive classes of cobia Rachycentron canadum , caught along the Gulf of Mexico and the south-east Atlantic coast of the U.S.A., are described during the annual reproductive cycle. These are based upon changes in the testicular germinal epithelium and the stages of germ cells that are present: early maturation, mid maturation, late maturation, regression and regressed. During early maturation, the germinal epithelium is continuous from the testicular ducts to the periphery of the testis and active spermatogenesis occurs throughout the testis. In mid maturation, the germinal epithelium near the ducts becomes discontinuous, but it remains continuous distally. In late maturation, a discontinuous germinal epithelium extends all along the lobules to the testicular periphery; lobules are swollen with sperm and there is minimal spermatogenesis. The regression class is characterized by a discontinuous epithelium throughout the testis, sperm storage and widely scattered spermatocysts. Spermatogonial proliferation also occurs along the lobule walls and at the periphery of the testis. In regressed testes, spermatogonia exist only in a continuous or discontinuous germinal epithelium, although residual sperm are nearly always present in the lobules and ducts. The presence or absence of sperm is not an accurate indicator of reproductive classes. At the periphery of the testis in the regression and regressed classes, the distal portions of lobules elongate as cords of cells containing spermatogonia and Sertoli cells. All reproductive classes can be identified in paraffin sections, although plastic sections provide better resolution. Using maturation classes defined by changes in the germinal epithelium to describe testicular development and spermatogenesis gives a more accurate picture than does using the traditional terminology.     

Involvement of the gonadal germinal epithelium during sex reversal and seasonal testicular cycling in the protogynous swamp eel,Synbranchus marmoratus Bloch 1795 (Teleostei,Synbranchidae)

The swamp eel, Synbranchus marmoratus, is a protogynous, diandric species. During sex reversal, the ovarian germinal epithelium, which forms follicles containing an oocyte and encompassing follicle cells during the female portion of the life cycle, produces numerous invaginations, or acini, into the ovarian stroma. Within the acini, the gonia that formerly produced oocytes become spermatogonia, enter meiosis, and produce sperm. The acini are bounded by the basement membrane of the germinal epithelium. Epithelial cells of the female germinal epithelium, which formerly became follicle (granulosa) cells, now become Sertoli cells in the developing testis. Subsequently, lobules and testicular ducts form. The swamp eel testis has a lobular germinal compartment in both primary and secondary males, although the germinal compartment in testes of secondary males resides within the former ovarian lamellae. The germinal compartment, supported by a basement membrane, is composed of Sertoli and germ cells that give rise to sperm. Histological and immunohistochemical techniques were used to describe the five reproductive classes that were observed to occur during the annual reproductive cycle: regressed, early maturation, mid-maturation, late maturation, and regression. These classes are differentiated by the presence of continuous or discontinuous germinal epithelia and by the types of germ cells present. Synbranchus marmoratus has a permanent germinal epithelium. Differences between the germinal compartment of the testes of primary and secondary males were not observed.     

Morphofunctional changes of female germinal epithelium to support spermatozoa along the annual reproductive cycle in an inseminating catfish (Trachelyopterus galeatus,Auchenipteridae)

The reproductive system of some fish species presents elaborate mechanisms by which the females store spermatozoa inside their ovaries, keeping them viable for fertilization for an extended period of time. However, as intriguing as this sperm storage is, it is not yet understood how the sperm can remain viable in the ovary. Aiming to understand this phenomenon, the epithelium covering the ovarian lamellae, that is, the germinal epithelium, of the Cangati (Trachelyopterus galeatus), an inseminating catfish, was evaluated taking into account the different stages of the annual reproductive cycle. The germinal epithelium morphology changed during the annual reproductive cycle, presumably in preparation to receive the spermatozoa and keep them viable until fertilization. There was a progressive increase of the epithelium height. Also the number of intercellular junctions, desmosomes, and extended tight junctions, apparently increased forming chains that could be regarded as a barrier to isolate the sperm from the female immune system. Synthetic organelles were active releasing cytoplasmic granules and secretion in the epithelial enfolds in which the spermatozoa were deeply embedded. Concomitantly, oogonium nests were formed in the germinal epithelium during early folliculogenesis. J. Morphol. 275:65–75, 2014. © 2013 Wiley Periodicals, Inc.     

Derived sperm morphology in the interstitial sea cucumber Rhabdomolgus ruber,with observations on oogenesis and spawning behavior

Some life history features of the interstitial sea cucumber Rhabdomolgus ruber are described from intertidal specimens collected from the northern coast of Maine. Histological studies suggest that the population consists of hermaphrodites with gametogenesis being initiated in April and reproduction beginning in May and continuing through the summer months. Sexually mature adults possess a single, blind‐ended gonadal tubule that functions as an ovotestis by producing both eggs and sperm. The ovotestis wall consists of an outer peritoneum composed of flagellated epithelial cells and muscles; an inner germinal epithelium of germ and somatic cells; and a middle connective tissue (hemal) compartment bounded by the basal laminas of the peritoneum and germinal epithelium. During the reproductive season, the gonadal tubule contains all stages of oocyte development. Vitellogenesis appears to involve the biosynthetic activities of the Golgi complex and rough endoplasmic reticulum. A few specimens had transitional ovotestes with mature sperm in the gonad lumen and asynchronously developing oocytes and a small number of spermatocytes within the germinal epithelium. The mature spermatozoon is an ent‐aquasperm with ultrastructural features significantly different from those described from other echinoderm classes including a highly elongated acrosome, a large periacrosomal region between the acrosome and nucleus, numerous unfused mitochondria in the midpiece, and a cytoplasmic sleeve or collar extending posteriorly along the proximal portion of the flagellum. The sperm head reaches 11.5 μm in length (combined midpiece, nucleus, periacrosomal region, acrosome), making it the longest yet reported from the Holothuroidea and among the longest in the Echinodermata. Some elements of this derived morphology could be attributed to fertilization biology, but others may have phylogenetic significance. Spawning behavior was observed in which two individuals appeared to pseudocopulate by intertwining their oral tentacles for several minutes before one of them abruptly secreted an egg mass containing three eggs.     

Testicular maturation and regression in the common snook

During the annual reproductive cycle, the lobular testis of Centropomus undecimalis undergoes height, width, and morphological changes which reflect five reproductive classes: regressed; early, mid-, and late maturation; and regression. Histological criteria, particularly differences between continuous and discontinuous germinal epithelia, are used to distinguish these five classes, even though they are only reference points within the annual gonadal cycle. A mechanism for lobular growth during early, mid-, and late maturation is presented; and it is hypothesized that a permanent germinal epithelium first appeared in the fishes. Throughout the year, periodic acid-Schiff-positive macro-melanophage centres and PAS-positive granulocytes are observed in the testis. They are most abundant after the breeding season, and they may be involved in focal tissue degradation.     

Ontogenetic testicular development and spermatogenesis in rays: the Cownose Ray,Rhinoptera bonasus,as a model

An understanding of testicular anatomy, development, and seasonality has implications for studies of morphology, behavior, physiology, and bioenergetics of males. Ontogenetic testicular development and spermatogenesis is essentially unknown for chondrichthyans. We examined embryo, juvenile, and adult male Cownose Rays (Rhinoptera bonasus) during development and throughout the annual reproductive cycle. Spermatogonia and Sertoli cells originated from germ cells and somatic cells, respectively, in the embryonic testicular germinal epithelium. In embryos and small juveniles, discrete regions of spermatocyst production appeared within a series of papillae that projected from the dorsal surface of each testis. Because these papillary germinal zones appeared to proliferate through ontogeny, we hypothesize that (1) the germinal zones of juvenile and adult testes are derived from embryonic testicular papillae that form from the germinal epithelium and (2) the papillae become the dorso-central portion of the distinct testicular lobes that form at maturation due to increased spermatocyst production. Our observations indicate that testicular development and the process of spermatogenesis began during embryonic development and increased in scale through ontogeny until maturation, when distinct testicular lobes formed and began enlarging or shrinking based on the annual reproductive cycle. Gonadosomatic indices peaked corresponding to seasonal increased sperm production between January and April, just prior to the April–June mating period. In all life stages, spermatocysts had efferent ducts associated with them from their formation through all stages of development. Year-round presence in the Charlotte Harbor estuarine system, Florida made R. bonasus a good model for beginning to understand ontogenetic gonad development and spermatogenesis in chondrichthyans, especially viviparous rays.     

Proliferation of Oogonia and folliculogenesis in the viviparous teleost Ilyodon whitei (Goodeidae)

Oogonial proliferation in fishes is an essential reproductive strategy to generate new ovarian follicles and is the basis for unlimited oogenesis. The reproductive cycle in viviparous teleosts, besides oogenesis, involves development of embryos inside the ovary, that is, intraovarian gestation. Oogonia are located in the germinal epithelium of the ovary. The germinal epithelium is the surface of ovarian lamellae and, therefore, borders the ovarian lumen. However, activity and seasonality of the germinal epithelium have not been described in any viviparous teleost species regarding oogonial proliferation and folliculogenesis. The goal of this study is to identify the histological features of oogonial proliferation and folliculogenesis during the reproductive cycle of the viviparous goodeid Ilyodon whitei. Ovaries during nongestation and early and late gestation were analyzed. Oogonial proliferation and folliculogenesis in I. whitei, where intraovarian gestation follows the maturation and fertilization of oocytes, do not correspond to the late oogenesis, as was observed in oviparous species, but correspond to late gestation. This observation offers an example of ovarian physiology correlated with viviparous reproduction and provides elements for understanding the regulation of the initiation of processes that ultimately result in the origin of the next generation. These processes include oogonia proliferation and development of the next batch of germ cells into the complex process of intraovarian gestation. J. Morphol. 275:1004–1015, 2014. © 2014 Wiley Periodicals, Inc.     

Duration of spermatogenesis and daily sperm production in the jaguar (Panthera onca)

The jaguar, like most wild felids, is an endangered species. Since there are few data regarding reproductive biology for this species, our main goal was to investigate basic aspects of the testis and spermatogenesis. Four adult male jaguars were utilized; to determine the duration of spermatogenesis, two animals received an intratesticular injection of H(3)-thymidine. Mean (+/-SEM) testis weight and the gonadosomatic index were 17.7+/-2.2g and 0.05+/-0.01%, respectively, whereas the seminiferous tubules and the Leydig cells volume density were 74.7+/-3.8 and 16.7+/-1.6%. Eight stages of spermatogenesis were characterized, according to the tubular morphology system and acrosome development. Each spermatogenic cycle and the entire spermatogenic process (based on 4.5 cycles) lasted approximately 12.8+/-0.01 and 57.7+/-0.07 d. The number of Sertoli and Leydig cells per gram of testis was 29+/-4x10(6) and 107+/-12x10(6). Based on the number of round spermatids per pachytene spermatocyte (2.8+/-0.3:1; meiotic index); significant cell loss (30%) occurred during the two meiotic divisions. There were approximately eight spermatids for each Sertoli cell (Sertoli cell efficiency), whereas the daily sperm production per gram of testis was 16.9+/-1.2x10(6). We expect that in the near future, the knowledge obtained in the present investigation will facilitate, utilizing germ cell transplantation, preservation of the germinal epithelium and the ability to generate sperm from jaguars in testes of domestic cats.     

Sperm Quantity Explains Age-Related Variation in Fertilization Success in the Hide Beetle

Age-related variation in sperm quality and quantity may have a dramatic impact on female fecundity and fertilization success. Despite this, the relationships between these parameters are rarely investigated. Moreover, studies exploring age-related variation in male mating success generally fail to consider the entire lifespan of an individual male; instead they restrict analyses to a small number of defined age classes. As a consequence they are unable to assess the impact of early and late life history components on male reproductive success. In this study, we explore these questions using the hide beetle, Dermestes maculatus , a model species for investigating age-related male mating success. We first employed a longitudinal design to explore whether patterns of sperm transfer and subsequent reproductive success varied over the reproductive lives of a cohort of males. Secondly, we investigated age-related variation in sperm viability, a surrogate measure of sperm quality. Finally, we combined these data and assessed whether the observed patterns of sperm transfer were correlated with fertilization success. We found that the quantity of sperm varied with male age: the amount of sperm transferred to a female increased with male age until 9 wk and then started to decline. Similarly, female fecundity and fertilization success were related to male age: females mating with males when they were relatively young (1 wk) or relatively old (13 wk) suffered reductions in fecundity and fertilization. Our data suggest that fertilization success is driven at least in part by the quantity of sperm transferred during mating.     

Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Structure and function of seminal vesicles of Orthoptera Tettigonioidea

The epithelium of seminal vesicles of seven species of Orthoptera Tettigonioidea was examined. Results revealed an epithelium that is always monolayered and devoid of cuticular intima, thus reflecting its mesodermic origin. In some species epithelial secretory activity is intense and seems to be effected via both apocrine and merocrine mechanisms. A peculiar characteristic observed in most of the species examined consists in the presence of spermiophagic activity, never previously recorded in insect seminal vesicles which have usually been attributed the function of synthesizing the substances that maintain sperm viable during their storage therein. The probable role of this spermiophagic activity in relation to the reproductive biology of Orthoptera Tettigonioidea is discussed.     

Differences in sperm morphology in foam‐nesting leptodactyline frogs (Anura,Leptodactylidae)

Sperm morphology is diverse among vertebrates and is influenced by the reproductive strategies adopted by species. In anurans, sperm morphology is associated with reproductive modes and mating systems. Here, we describe the sperm morphology of 11 frog species in the genus Leptodactylus and that of Lithodytes lineatus and discuss the relationship between sperm morphology and species' mating systems. We observed two distinct sperm morphotypes among the leptodactyline species, which differed mostly in head morphology. Type I sperm had triangular head, discrete acrosome vesicle with posterior margin not clearly visible; type II sperm had elongated head, clear acrosomal vesicle with posterior margin clearly visible. These sperm types do not seem to be associated with phylogeny; instead, type II sperm was observed in all polyandrous species analysed and in species with evidences of polyandry. Moreover, sperm of all species presented tail with undulating membrane connected to the axial fibre. We suggest that differences in sperm morphology might be associated with sperm competition to what polyandrous species are subjected. However, natural history observations on polyandrous mating in some species presenting type II sperm and phylogenetic comparative studies are need to elucidate the role of mating systems in the evolution of sperm morphology in leptodactylines.     

Functional morphology of the sperm-containing chambers of the sea slug Okenia polycerelloides in the context of sexual selection

Sea slugs are interesting models to study post-copulatory sexual selection in simultaneous hermaphrodites due to the enormous variation of their reproductive systems. However, the knowledge of the functional morphology of their reproductive system is limited to few species, and it is rarely discussed in the context of sexual selection theory. In this study, we investigated the functional morphology of the sperm-containing chambers (i.e., ampulla, seminal receptacle, and bursa copulatrix) of the reproductive system of Okenia polycerelloides (Ortea & Bouchet, 1983), based on light, confocal, and electron microscopy. Although the morphology of the ampulla is similar to other species, indicating that it is a site for autosperm storage, we found some sperm facing the ampullar epithelium, a feature commonly regarded as characteristic of the seminal receptacle of sea slugs. The seminal receptacle of O. polycerelloides showed secretory activity and contained sperm with distribution and orientation suggestive of stratification of allosperm from distinct mating events, a feature that would affect sperm competition. The bursa copulatrix had epithelial cells with secretory and absorptive characteristics, and contained degraded sperm and yolk granules within its lumen. Comparative analyses of the contents of each organ demonstrated that sperm digestion occurs in the bursa copulatrix and affects sperm heads first, changing their morphology from slender and curved to shorter and ellipsoid before complete lysis. Although digestion and absorption of surplus sperm are currently the main hypothesized functions for the bursa copulatrix, its role in cryptic female choice should not be ruled out. The close structural connection between the seminal receptacle and bursa copulatrix, as well as their muscular walls, would enable control over the fate of the sperm received in each mating event, that is, storage or digestion.     

Sperm storage and spermatozoa interaction with epithelial cells in oviduct of Chinese soft‐shelled turtle,Pelodiscus sinensis

Spermatozoa are known to be stored within the female genital tract after mating in various species to optimize timing of reproductive events such as copulation, fertilization, and ovulation. The mechanism supporting long‐term sperm storage is still unclear in turtles. The aim of this study was to investigate the interaction between the spermatozoa and oviduct in Chinese soft‐shelled turtle by light and electron microscopy to reveal the potential cytological mechanism of long‐term sperm storage. Spermatozoa were stored in isthmus, uterine, and vagina of the oviduct throughout the year, indicating long‐term sperm storage in vivo. Sperm heads were always embedded among the cilia and even intercalated into the apical hollowness of the ciliated cells in the oviduct mucosal epithelium. The stored spermatozoa could also gather in the gland conduit. There was no lysosome distribution around the hollowness of the ciliated cell, suggesting that the ciliated cells of the oviduct can support the spermatozoa instead of phagocytosing them in the oviduct. Immune cells were sparse in the epithelium and lamina propria of oviduct, although few were found inside the blood vessel of mucosa, which may be an indication of immune tolerance during sperm storage in the oviduct of the soft‐shelled turtle. These characteristics developed in the turtle benefited spermatozoa survival for a long time as extraneous cells in the oviduct of this species. These findings would help to improve the understanding of reproductive regularity and develop strategies of species conservation in the turtle. The Chinese soft‐shelled turtle may be a potential model for uncovering the mechanism behind the sperm storage phenomenon.     

Queen-worker differences in spermatheca reservoir of phylogenetically basal ants

Ant queens mate when young and store sperm in their spermatheca to fertilize eggs for several years until their death. In contrast, workers in most species never mate. We have compared the histological organization of spermathecae in 25 poneromorph species exhibiting various degrees of queen-worker dimorphism. The spermathecae of both castes in all species are similar in having a reservoir connected by a sperm duct to the ovary, and a paired gland opening into this duct. The reservoir of queens typically has a columnar epithelium in the hilar region (near the opening of the sperm duct), whereas the epithelium in the distal region is cuboidal. Abundant mitochondria together with apical microvilli and basal invaginations indicate an osmoregulatory function. In contrast, the reservoir epithelium of workers is flattened throughout and lacks these transport characteristics. This single difference shows the importance of a columnar epithelium in the reservoir for sperm storage. However, our data have not revealed inter-specific variations in the development of the hilar region linked with higher fecundity. We have found no consistent differences in associated structures, such as the spermatheca gland or sperm ducts, or in the musculature between queens and workers.This work was funded by IWT, FWO, KULeuven OT and JSPS.     

Functional anatomy of the female reproductive systems of two spider crabs (Decapoda,Majoidea)

To better understand the mating systems of majoid crabs, we studied the functional anatomy of the female reproductive systems of the spider crabs Leurocyclus tuberculosus and Libinia spinosa, comparing them with those of other Majoidea. Adult females were measured and dissected, and their reproductive systems described macroscopically and histologically. In females of both species, the seminal receptacles are paired globular structures of ecto‐mesodermal origin. The mesoderm‐derived region is lined by a stratified epithelium. The anchoring, proliferative, and secretory strata are clearly recognizable . The ectoderm‐derived region is lined by a simple cylindrical epithelium underlying a cuticle that increases in thickness toward the vagina. The transition between the ectoderm and mesoderm‐derived regions is abrupt, with differences between the studied species: Li. spinosa has a “velum,” whereas Le. tuberculosus presents prominent “folds.” In both species, the position in which the oviduct is connected to the seminal receptacles is intermediate between the dorsal and ventral types previously described in other eubrachyurans. The seminal receptacles of the studied species show four different conditions, which can be distinguished macroscopically based on their shape and amount of sperm stored. We compare our data with those from other Majoidea in an attempt to determine whether the morphology of the seminal receptacles is related to different mating strategies or behaviors.     

Mixed reproductive strategy in Tubifex tubifex (Oligochaeta, Tubificidae)?

Despite the wide use of the tubificid oligochaete Tubifex tubifex in eco-toxicological studies, the reproductive strategy adopted by the species, that can reasonably be assumed to be the key to its ecological success, is still not well investigated. This study reports on breeding experiments analysed by allozyme markers (Pgi, Pgm, and Idh), accompanied by a study of the sperm production in the species, with the aim to: (1) clarify the type of uniparental reproduction adopted by the species, (2) test the hypothesis that uniparental reproduction is reversible, (3) investigate the occurrence of biparental reproduction in laboratory cultures. Studies of parent-offspring comparison at polymorphic allozyme loci showed parthenogenetic reproduction and maintenance of asexuality in the parthenogenetic individuals. A cross-breeding test performed with couples made up of randomly assorted individuals, whose genotype combinations were suitable for discriminating between sexual and asexual reproduction, failed to show biparental reproduction in laboratory cultures: T. tubifex always reproduced parthenogenetically. Unexpectedly, spermiogenetic analysis indicated that both kinds of sperm produced by the species (eusperm and parasperm) were differentiated in individuals raised either in cohort cultures or in isolation (first, second, and third parthenogenetic generations), with a similar pattern of sperm production correlated to the sexual stage. Interestingly, there was no avoidance of mating in any of the collective cultures analysed. Concomitance between parthenogenetic reproduction and a "normal" male functionality, which is typical of a sexually reproducing species, could be justified by a mixed reproductive strategy or a pseudogamy process occurring in T. tubifex. However, several aspects of the reproductive behaviour of the species deserve further investigation.     

Mapping of the human testicular proteome and its relationship with that of the epididymis and spermatozoa

The testis produces male gametes in the germinal epithelium through the development of spermatogonia and spermatocytes into spermatids and immature spermatozoa with the support of Sertoli cells. The flow of spermatozoa into the epididymis is aided by testicular secretions. In the epididymal lumen, spermatozoa and testicular secretions combine with epididymal secretions that promote sperm maturation and storage. We refer to the combined secretions in the epididymis as the sperm-milieu. With two-dimensional-PAGE matrix-assisted laser desorption ionization time-of-flight MS analysis of healthy testes from fertile accident victims, 725 unique proteins were identified from 1920 two-dimensional-gel spots, and a corresponding antibody library was established. This revealed the presence of 240 proteins in the sperm-milieu by Western blotting and the localization of 167 proteins in mature spermatozoa by ICC. These proteins, and those from the epididymal proteome (Li et al. 2010), form the proteomes of the sperm-milieu and the spermatozoa, comprising 525 and 319 proteins, respectively. Individual mapping of the 319 sperm-located proteins to various testicular cell types by immunohistochemistry suggested that 47% were intrinsic sperm proteins (from their presence in spermatids) and 23% were extrinsic sperm proteins, originating from the epididymis and acquired during maturation (from their absence from the germinal epithelium and presence in the epididymal tissue and sperm-milieu). Whereas 408 of 525 proteins in the sperm-milieu proteome were previously identified as abundant epididymal proteins, the remaining 22%, detected by the use of new testicular antibodies, were more likely to be minor proteins common to the testicular proteome, rather than proteins of testicular origin added to spermatozoa during maturation in the epididymis. The characterization of the sperm-milieu proteome and testicular mapping of the sperm-located proteins presented here provide the molecular basis for further studies on the production and maturation of spermatozoa. This could be the basis of development of diagnostic markers and therapeutic targets for infertility or targets for male contraception.     

Functional morphology of the gonoduct of the viviparous teleost Poeciliopsis gracilis (Heckel, 1848) (Poeciliidae)

Female teleosts do not develop Müllerian ducts; consequently, the ovary of teleosts contains two zones: germinal and gonoduct. The gonoduct lacks germinal cells, but has relevant functions in the reproductive process. We describe the functional morphology of the gonoduct in the viviparous teleost Poeciliopsis gracilis during nongestation and gestation stages. This study tests the hypothesis that the gonoduct functions as a barrier between the germinal zone and the exterior. By providing information about morphology and function of the gonoduct we show that this part of the ovary has an essential role in the reproduction of teleosts. The ovaries were processed by histological technique and stained with hematoxylin‐eosin (H‐E), Masson's trichrome, toluidine blue and periodic acid‐Schiff (PAS). The gonoduct is divided into three regions: cephalic, middle, and caudal. In the cephalic and middle regions there are mucosal folds that extend into the gonoductal lumen, forming structures similar to a cervix. The caudal region has two portions: the anterior contains a dorsal invagination and exocrine glands among columnar cells; the posterior has a ventral flexion and stratified epithelium with apical secretory cells. The morphology of this epithelium indicates two functions: (a) secretory by the apical columnar cells, and (b) protection through the stratification. Another peculiarity of the caudal region is that both ducts, reproductive and digestive, converge in a common cavity at their caudal ends, forming a cloacal region. The histology of the gonoduct indicates relevant functions including: (1) the control of the luminal diameter by the muscle and the presence of mucosal folds, like a cervix; (2) the relationship with the spermatozoa during insemination and storing them in mucosal folds; (3) the support of immunological processes; (4) secretory activities; (5) forming the duct during birth; and (6) possibly, acts as a barrier against parasite infestations.