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.     

Reproduction of the internal inseminator Trachelyopterus galeatus (Linnaeus, 1766) (Siluriformes: Auchenipteridae)

Studied was the reproductive activity of Trachelyopterus galeatus using microscopic analyses of gonads and biological indices. To evaluate the reproductive biology of T. galeatus, which is an important species in the Jequitinhonha River basin, Minas Gerais, Brazil, 254 males and 372 females were captured between May 2012 and April 2013 from the Irapé Reservoir using gillnets with meshes of various sizes. Average total length of males was 13.3 ± 2.1 and 14.3 ± 2.3 cm for females. Females were more abundant than males (1.4 females:1 male) in all total length classes. The reproductive peak of T. galeatus occurred between November and February, when the biological indices related to reproduction were highest and the physical‐chemical water parameters were most favourable for reproduction in this Neotropical environment. Trachelyopterus galeatus reproduces throughout the year and is a partial spawner.     

Morphology and histology of male and female reproductive systems in the inseminating species Scoloplax distolothrix (Ostariophysi: Siluriformes: Scoloplacidae)

The morphology and histology of male and female reproductive systems were examined in Scoloplax distolothrix. Internal insemination was documented in this species by the presence of sperm within the ovaries. Mature males and females have elongated genital papillae, exhibiting a tubular shape in males and a plain heart‐shape with two median protuberances in females. The testes are two elongated structures that converge ventrally, under the intestine, towards the genital papilla. They are joined at the caudal end, forming an ovoid single chamber for sperm storage. Secretory regions were not observed. In the lumen of the testicular tubules, spermatozoa can be tightly packed along their lengths, but do not constitute a spermatozeugmata. The lumen of the sperm storage chamber and spermatic duct are filled with free spermatozoa without the accompanying secretions. The ovaries are bird‐wing shaped, saccular structures that converge ventrally under the intestine, towards the genital papilla. They are joined at the caudal end, forming a tubular chamber possibly destined for oocyte storage. An oviduct with an irregular outline connects the chamber to the tubular region of the genital papilla. No distinct sperm storage structure was found in the ovaries. The unique male and female genital papillae suggest that these structures are associated with the reproductive mode in scoloplacids, representing evidence for insemination. The occurrence of free spermatozoa, without the accompanying secretions and not arranged in a spermatozeugmata can be associated with the presence of a tubular male genital papilla for sperm transfer to the female genital tract. This reinforces the idea that sperm packets are not necessary for all inseminating species. The male reproductive system in scoloplacids is very different from that in auchenipterids, a second catfish family with insemination, which indicates that the occurrence of insemination is not connected to the internal morphology of reproductive organs. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

A molecular assessment of species diversity in Tympanopleura and Ageneiosus catfishes (Auchenipteridae: Siluriformes)

In order to test the congruence of genetic data to the morphologically defined Neotropical catfish genera Tympanopleura and Ageneiosus and explore species diversity, we generated 17 DNA barcodes from five of six species of Tympanopleura and 12 of 13 species of Ageneiosus. To discriminate limits between species, an automatic barcode gap discovery (ABGD), a generalised mixed yule-coalescent model (GYMC) and fixed distance thresholds Kimura two-parameter (K2P; 3%) were used to discriminate putative species limits from the DNA barcodes. The ABGD, GMYC and K2P methods agreed by each generating 13 clusters: six in Tympanopleura (five nominal plus one undescribed species) and seven in Ageneiosus. These clusters corresponded broadly to the described species, except in the case of the Ageneiosus ucayalensis group (A. akamai, A. dentatus, A. intrusus, A. ucayalensis, A. uranophthalmus and A. vittatus). Haplotype sharing and low divergences may have prevented molecular methods from distinguishing these species. We hypothesise that this is the result of a recent radiation of a sympatric species group distributed throughout the Amazon Basin. One putative new species of Tympanopleura was also supported by the molecular data. These results taken together highlight the utility of molecular methods such as DNA barcoding in understanding patterns of diversification across large geographic areas and in recognising overlooked diversity.     

Variation of male reproductive apparatus in relation to fertilization modalities in the catfish families Auchenipteridae and Callichthyidae (Teleostei: Siluriformes)

To investigate the relationship between fertilization modalities and the morphology of male reproductive apparatus, two species of Auchenipteridae, Auchenipterus nuchalis and Tatia intermedia , and six species of Callichthyidae, Callichthys callichthys , Corydoras aeneus , Corydoras bondi , Corydoras ehrhardti , Corydoras potaroensis and Hoplosternum littorale were studied. The species analysed show either internal or external fertilization, the latter including the so called 'sperm drinking' type of mating. An anal fin modified as an intromittent organ, a pair of seminal vesicles, and the release of sperm in the form of discrete bundles (spermatozeugmata) characterize the male reproductive apparatus of the internal fertilizer A. nuchalis . Seminal vesicles are present also in C. aeneus , C. bondi , C. ehrhardti , C. potaroensis and H. littorale , species performing 'sperm drinking' spawning. In contrast, regardless of the family, species showing the more classic type of external fertilization lack specialized accessory organs. Where occurring, the major function of seminal vesicles is the secretion of mucins. The role of these mucosubstances, in relation to spermatozeugmata formation, in internal fertilizers, or the protection of sperm passing through the female gut, in the 'sperm-drinking' species, is discussed. Variation, between families, in the shape of testis and accessory structures, as well as in the type of spermatogenesis was found. Neither the reproductive modalities nor the phylogenetic relationships, however, appear to fully account for these differences.     

Morphology of the male reproductive systems of two Indopacific blenniid fishes,Salarias fasciatus and Ecsenius bicolor (Blenniidae,Teleostei)1

The testes and associated accessory organs of two blenniid fishes are described. The testicular organs of Salarias fasciatus consist of a testicular gland adjacent to the testis, chambered seminal vesicles serving as a reservoir for spermatozoa and testicular blind ouches. Ecsenirts bicolor has no testicular gland, has elongated chambered seminal vesicles whii are not used as a reservoir for spermatozoa, and has testicular blind pouches.     

Morphology of male reproductive system in three species of Trypoxylon (Trypargilum) Richards (Hymenoptera: Crabronidae)

Variations in the adult male reproductive system among different groups of Hymenoptera offer characteristics that help studies on behavior and phylogenetics. The objective of this study was to describe the adult male reproductive system of three Trypoxylon (Trypargilum) species. For that, tissues were disseced, fixed in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer, pH 7.2 and postfixed in 1% osmium tetroxide. The material was dehydratated and embedded for light and electron transmission microscopes. The species have similar reproductive systems, which are formed by a pair of testes, each one with three fusiforme follicles, from which emerges an efferent duct that later joins forming a deferent duct. The deferent duct opens into an ejaculatory duct. The first half of the deferent duct is enlarged and differentiated in a region specialized in sperm storage, the seminal vesicle. The accessory gland flows in the post-vesicular region of the deferent duct. The testes and vesicles are both covered with a conjunctive capsule. Sexually mature individuals have all spermatogenesis stages in their follicles. Sperms are released from testes in bundles which are disorganized inside seminal vesicles.     

Sperm and spermatozeugma ultrastructure in the inseminating species Tyttocharax cochui, T. tambopatensis, and Scopaeocharax rhinodus (Pisces: Teleostei: Characidae: Glandulocaudinae: Xenurobryconini)

This article presents the scanning and transmission electron microscopy of the spermatozoa and sperm packets of three inseminating species of the glandulocaudine tribe Xenurobryconini. All three species, Scopaeocharax rhinodus, Tyttocharax cochui, and T. tambopatensis produce unencapsulated sperm packets (= spermatozeugmata) of similar morphology. The external anterior surface of each spermatozeugma is comprised of elongate sperm heads arranged in parallel, and the posterior part is made up of tightly packed flagella. The interior of the anterior portion consists of alternating layers of sperm heads and flagella. The remarkable integrity of each packet appears to be maintained through an electron-dense secretion seen among all parts of the cells. Spermatozeugma formation takes place within the spermatocysts at the end of spermiogenesis and at spermiation fully formed packets are released. Morphology of the mature spermatozoa was similar in all three species. Each nucleus is elongate, flattened along most of its length, and tapers at either end. The two centrioles are nearly parallel to one another and are located just anterior to the nucleus. Elongate mitochondria are located along the nucleus. The single flagellum, which lacks axonemal fins, is initially contained within a short cytoplasmic collar. Accessory microtubules run parallel to the long axis of the nucleus just beneath the plasma membrane. During spermiogenesis, no nuclear rotation occurs and the cytoplasmic canal containing the flagellum elongates along with the nucleus. However, prior to spermiation all but the anterior portion of the collar degenerates. The sperm modifications observed in these species are discussed as adaptations to the unique reproductive habit of insemination.     

Comparative morphology of the gonadal structure related to reproductive strategies in six species of neotropical catfishes (Teleostei: Siluriformes)

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full‐grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied. © 2011 Wiley‐Liss, Inc.     

Fine structure of the male reproductive system in two species ofHaplognathia sterrer (Gnathostomulida,Filospermoidea)

Summary The structure of the male reproductive systems of two species ofHaplognathia cf.lyra andH. cf.rosacea was described. The structure of the testes and the anterior portions of the sperm ducts in both species was found to be similar. However, considerable species differences were found between the structures of the glands and muscles associated with the reproductive systems. These were more elaborate inH. cf.lyra than inH. cf.rosacea. The former species possessed an H-shaped sperm duct gland, three distinct groups of penis muscles and a penis with two cell types and with a lumen. The latter species had paired sperm duct glands, no specialized penis muscles and a penis with only one cell type and without a detectable lumen. No open gonopore was observed in either species. The sperm presumably exit through a ventral tissue connection observed connecting the penis and the ventral epidermis. These findings were discussed in the light of Mainitz's (1977) theory concerning the primitive penis type within the Gnathostomulida.Abbreviations ap anterior-posterior penis muscles - bm basement membrane - csd common sperm duct - dl dorsal lumen of the penis - dp dorsal gland cells of the penis - dv dorsoventral muscles anterior to the penis - dw sperm duct wall cell - e epidermis - ex exit cell - g intestine - gl gut lumen - n nerve - p penis - sd sperm duct - sdg sperm duct gland - tw testes wall cell - vl ventral lumen of the penis - vp ventral gland cells of the penis This project was supported by NSF grant #GB 42211 (R.M. Rieger P.I.). The line drawings have been executed after our design by Ms. Linda McVay     

Peculiarities of the male urogenital apparatus of two grunt species (Teleostei, Haemulidae)

An unusual testicular structure in the white grunt, Haemulon plumieri , and the French grunt, H. flavolineatum , and a urinary exocrine gland in H. flavolineatum are described. The testes of both species are comprised predominantly of efferent ducts, with spermatogenetic tissue restricted to the gonadal periphery. The epithelial cells of the efferent ducts produce glycogen which may serve a role in the storage and nutrition of sperm. The urinary gland is a male accessory gland thought to be associated with reproduction. The gland is mesonephric in origin and the epithelial cells of the gland produce mucins which may be involved in intraspecific chemical communication.     

Reproductive apparatus and male accessory structures in two batrachoid species (Teleostei, Batrachoididae)

The morphology of the genital apparatus of two batrachoid species, Opsanus tau and Porichthys notatus , was studied. The anatomical organization of the female reproductive apparatus is similar in both species but differences are observed in the rhythm of gametogenesis with individual oocyte production asynchronous in O. tau and group synchronous in P. notatus. The male reproductive apparatus is similarly organized in the two species, with both showing enlongated testes with an efferent duct system, two main testicular ducts, a common sperm duct, and a pair of multi-channel accessory structures. The sperm transport system consisting of the efferent duct system, main testicular ducts, and sperm duct is more developed in P. notatus and only in this species does it secrete sialoglycoproteins. Male accessory organs also secrete sialoglycoprotein in both species, but they appear more developed in O. tau. Intraspecific variability in development of accessory structures and mucin secretion was also observed between the two male morphs of P. notatus. Type I males, which build nests and perform parental care to eggs and fry, have larger accessory organs and more abundant secretion than type II males, which adopt opportunistic spawning tactics. The possible role played by mucins as components of the seminal fluid, in both species, and their inter-and intraspecific variability are discussed in the light of the reproductive biology and the presence of alternative male mating tactics.     

Comparative morphology of the gas bladder in driftwood catfishes (Siluriformes: Auchenipteridae)

The gross morphology of the gas bladder is described and illustrated for representatives of most species and all valid genera of the Auchenipteridae (Siluriformes). Although, a simple cordiform gas bladder is present in some species of the family, others are characterized by their distinctive gas‐bladder shape and diverticula disposition. An acute posterior end of the gas bladder characterizes Centromochlus heckelii and C. macracanthus, and is variably present in specimens of Auchenipterus. Tocantinsia piresi and Asterophysus batrachus have distinctive gas bladders differing in number of diverticula (two or many). The two species of Trachycorystes are diagnosed based on their gas bladder morphology: T. menezesi has a simple cordiform bladder, whereas T. trachycorystes has a pair of lateral diverticulum and, usually, a well‐developed terminal diverticulum. Species of Auchenipterichthys are characterized by having a secondary bladder with simple chamber. Short or elongate and divergent terminal diverticula are exclusive to most cis‐andine species of Trachelyopterus. Tetranematichthys and trans‐andine species of Trachelyopterus share a well‐developed secondary chamber or terminal diverticula ventrally or dorsally connected to the posterior chambers. The small‐sized species of Ageneiosus have well‐developed gas bladders with a pair of posterior diverticula, whereas large‐sized species have a reduced gas bladder with tunica externa varying from non‐, partially, or completely ossified. Eight phylogenetic characters are proposed based on the morphology of the gas bladder and associated structures in species of Auchenipteridae, and the evolution of those characters in the family discussed. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Morphology and histology of the oesophagus in a warmwater tilapiine fish (Teleostei)

The oesophagus morphology of an omnivorous tilapiine fish is described. This organ is very short and is organized into a mucosa, a submucosa, a double-layered muscolaris and a serosa. The epithelium is stratified with columnar cells, but the most peculiar feature is the presence of many goblet cells that assure protection and lubrication. Taste buds are not present.