The development of the digestive system and the fate of the yolk syncytial layer in postembryogenesis of Stenodus leucichthys nelma (Teleostei)

Stenodus leucichthys nelma is an economically important species for cold-water aquaculture. Unlike other Coregoninae, S. leucichthys nelma is a piscivore. Here, we describe in detail the development of the digestive system and the yolk syncytial layer from hatching to early juvenile stage using histological and histochemical methods to determine their common and specific characteristics and to test the hypothesis that the digestive system of S. leucichthys nelma rapidly acquires adult features. The digestive tract differentiates at hatching and starts to function before the transition to mixed feeding. The mouth and anus are open, mucous cells and taste buds are present in the buccopharyngeal cavity and esophagus, pharyngeal teeth have erupted, the stomach primordium is seen, the intestinal epithelium with mucous cells is folded and the intestinal valve is observed; the epithelial cells of the postvalvular intestine contain supranuclear vacuoles. The liver blood vessels are filled with blood. The cells of exocrine pancreas are loaded with zymogen granules, and at least two islets of Langerhans are present. However, the larvae remain dependent on maternal yolk and lipids for a long time. The adult features of the digestive system develop gradually, the most significant changes take place approximately from 31 to 42 days posthatching. Then, the gastric glands and pyloric caeca buds appear, the U-shaped stomach with glandular and aglandular regions develops, the swim bladder inflates, the number of islets of Langerhans increases, the pancreas becomes scattered, and the yolk syncytial layer undergoes programmed death during the larval-to-juvenile transition. During postembryonic development, the mucous cells of the digestive system contain neutral mucosubstances.

Seaweed Sargassum wightii mediated preparation of TiO2 nanoparticles, larvicidal activity against malaria and filariasis vectors, and its effect on non-target organisms

Malaria and Lymphatic filariasis are considered significant public health concerns in several countries. As a researcher, controlling those mosquitos using safe and eco-friendly insecticides is essential. Thus, we aimed to explore the potential use of seaweed Sargassum wightii for the biosynthesis of TiO2 NPs and evaluate its efficiency in controlling disease-transmitting mosquito larvae (using Anopheles subpictus and Culex quinquefasciatus larvae as model systems (in vivo)) as well as its potential effect on non-target organisms (using Poecilia reticulata fish as an experimental model). XRD, FT-IR, SEM-EDAX, and TEM carried out the characterization of TiO2 NPs. It evaluated the larvicidal activity against the fourth instar larvae of A. subpictus and C. quinquefasciatus. The larvicidal mortality was observed after 24 h of exposure to S. wightii extract and TiO2 NPs. S. wightii synthesized TiO2 NPs show excellent activity against A. subpictus and C. quinquefasciatus (LC50 = 4.37 and 4.68; LC90 = 8.33 and 8.97; χ2 = 5.741 and 4.531) mg/L respectively. The GC-MS results indicate the presence of some important long-chain phytoconstituents like linoleic acid, palmitic acid, oleic acid methyl ester, and stearic acid, among others. Furthermore, when testing the possible toxicity of biosynthesized NPs in a non-target organism, no adverse effects were observed in Poecilia reticulata fish exposed for 24 h, considering the evaluated biomarkers. Thus, overall, our study results reveal that biosynthesized TiO2 NPs are an effective and exciting eco-friendly approach to controlling the A. subpictus and C. quinquefasciatus.

Ovaries of guppies (Poecilia reticulata) investigated in pre-embryonic, embryonic and post-embryonic stages after exposure to maghemite nanoparticles (y-Fe2O3) associated with Roundup® and glyphosate, followed by recovery period evaluation

Iron oxide nanoparticles (IONP) are promising alternatives to environmental remediation, so this study investigates IONP single and associated to contaminants, in this case, glyphosate (GLY) and Roundup® (GBH) in Poecilia reticulata (guppy). The guppies have internal development, therefore this study analyzed female gonads to establish the developmental stages of P. reticulata and evaluate effects of exposure (7, 14 and 21 days) and post-exposure (same period) to the treatments with Iron ions 0.3mg Fe/L (IFe); IONP 0.3mg Fe/L; IONP 0.3 mgFe/L + GBH 0,65mgGLY/L (IONP+GBH1); IONP 0.3 mgFe/L + GBH 1.30 mgGLY/L (IONP+GBH2); and IONP 0.3 mgFe/L + GLY 0.65 mg/L (IONP+GLY). The development was organized in immature, development, and gestation phases. The damage in all treatments after 21 days of exposure was evident in reaction patterns regressive inflammatory, and circulatory including total histopathologic index of liver, nevertheless there was a damage recovery trend during post-exposure period.

New insights on folliculogenesis and follicular placentation in marine viviparous fish black rockfish (Sebastes schlegelii)

In viviparous fish, a considerable degree of variation in placental structures have been described. However, no distinct structures are reported in Scorpaenidae. In this study, we demonstrate a new type of folliculogenesis and follicular placentation in Sebastes schlegelii. Before copulation, the germinal epithelium gradually surrounds the oocytes and develops into individually follicles with a stalk-like structure hanging on the ovigerous lamella, which ensures each follicle have access to spermatozoa after copulation. From V to early gestation stage, the cyp17-I highly expressesaccompanied by cyp19a1a signals disappearance, and 11-ketotestosterone level keeps rising and peaks at blastula stage, while 17β-estradiol declines to the bottom. Meanwhile, the theca cells rapidly proliferate and invade outwards forming a highly hypertrophied and folded microvillous placenta. This unbalance of hormone might be an important factor driving the theca cells proliferation and invasion. Additionally, some conserved genes related to mammalian placentation are significantly high expression in follicular placenta suggesting the high convergence in vertebrate placenta evolution.

Intraovarian Gestation in Viviparous Teleosts: Unique Type of Gestation among Vertebrates

The intraovarian gestation, occurring in teleosts, makes this type of reproduction a such complex and unique condition among vertebrates. This type of gestation of teleosts is expressed in special morphological and physiological characteristic where occurs the viviparity and it is an essential component in the analysis of the evolutionary process of viviparity in vertebrates. In viviparous teleosts, during embryogenesis, there are not development of Müllerian ducts, which form the oviducts in the rest of vertebrates, as a result, exclusively in teleosts, there are not oviducts and the caudal region of the ovary, the gonoduct, connects the ovary to the exterior. The lack of oviducts defines that the embryos develop into the ovary, as intraovarian gestation. The ovary forms the oocytes which may develop different type of oogenesis, according with the storage of diverse amount of yolk, variation observed corresponding to the species. The viviparous gestation is characterized by the possible intimate contact between maternal and embryonic tissues, process that permits their metabolic interchanges. So, the nutrients obtained by the embryos could be deposited in the oocyte before fertilization, contained in the yolk (lecithotrophy), and may be completed during gestation by additional provisioning from maternal tissues to the embryo (matrotrophy). Then, essential requirements for viviparity in poeciliids and goodeids are characterized by: a) the diversification of oogenesis, with the deposition of different amount of yolk in the oocyte; b) the insemination, by the transfer of sperm to the female gonoduct and their transportation from the gonoduct to the germinal region of the ovary where the follicles develop; c) the intrafollicular fertilization; d) the intraovarian gestation with the development of embryos in intrafollicular gestation (as in poeciliids), or intraluminal gestation (as in goodeids); and, e) the origin of embryonic nutrition may be by lecithotrophy and matrotrophy. The focus of this revision compares the general and specific structural characteristics of the viviparity occurring into the intraovarian gestation in teleosts, defining this reproductive strategy, illustrated in this review with histological material in a poeciliid, of the species Poecilia latipinna (Lesueur, 1821) (Poeciliidae), and in a goodeid, of the species Xenotoca eiseni (Rutter, 1896) (Goodeidae).

Shedding light on the impacts of gestational exposure to polystyrene nanoplastics on the reproductive performance of Poecilia reticulata female and on the biochemical response of embryos

Although the toxicity of nanoplastics (NPs) has already been reported in experimental aquatic models, their possible effects on the reproductive performance of viviparous freshwater fish and their consequences for embryos, so far, are unknown. Thus, we aimed to evaluate whether the gestational exposure of Poecilia reticulata to polystyrene NPs (PS NPs) impacts the reproductive performance of females, induces teratogenic effects and/or predictive alterations of redox unbalance and cholinesterasic effect. Our results demonstrate that gestational exposure of P. reticulata females (for 30 days) to PS NPs (50 µg/L) affected reproductive aspects of the animals, inferred by the lower percentage of pregnancy and reduced offspring quantity. Although we did not observe teratogenic effect, we observed that the accumulation of PS NPs in embryos was significantly correlated with a redox unbalance, without, however, having a cholinesterasic effect (via evaluation of AChE and BChE activity) in embryos. Thus, by evidencing the accumulation of PS NPs in embryos of P. reticulata females exposed to the pollutant during the gestational period, we confirm not only the plausibility of the maternal transfer of these nanomaterials, but also their consequent physiological impacts on the offspring, which has not yet been demonstrated in live-bearing freshwater fish.

Gonad morphology of Rhyacichthys aspro (Valenciennes, 1837), and the diagnostic reproductive morphology of gobioid fishes

Rhyacichthys aspro is a “basal” taxon in the Suborder Gobioidei of the teleost order Gobiiformes. We provide detailed descriptions of the reproductive morphology of adult males and females to assess the diagnostic reproductive morphological characters of this speciose clade of bony fishes. Female R. aspro are asynchronous spawners: they are able to spawn more than once in a breeding season. Oocytes are inferred to have short attachment filaments. A conspicuous feature of the external anatomy of the reproductive system (RSy) of female R. aspro is an ornate fimbriate pad upon which the urogenital papilla rests. The male reproductive system is characterized by an intralobar collection system in both the testicular and secretory lobes, termed the “sperm‐collecting canal” and “milt‐collecting canal,” respectively. These may provide additional storage for sperm and milt. The spermatogenic lobe, or testis, is that portion of the male gobioid RSy comprising seminiferous lobules and separate from other RSy components. The secretory lobe is that portion of the male gobioid reproductive system that consists of secretory lobules and is separated from other components of the male RSy. The secretory lobe has also been called, in English, the sperm‐duct gland, accessory gonadal structure, or seminal vesicle, and is endorsed as a synapomorphy of gobioid fishes.

Morphological basis for maternal nutrient provision to embryos in the viviparous fish Ataeniobius toweri (Teleostei: Goodeidae)

In viviparous Mexican fishes of the family Goodeidae, embryos develop in the maternal ovarian lumen. They typically absorb maternal nutrients during gestation by means of "trophotaeniae," that is, specialized, elongated extensions of the hindgut that are exposed to the fluids, which occupy the ovarian lumen. The sole exception is Ataeniobius toweri, whose embryos lack trophotaeniae but are nevertheless matrotrophic. Thus, how its embryos obtain maternal nutrients is unclear. We studied a series of non-pregnant and pregnant ovaries of A. toweri using histology to identify the mechanism of maternal-embryo nutrient transfer. By early-gestation, embryos have depleted their yolk supplies. Yolks are released into the ovarian lumen and are ingested by the developing embryos, as shown by yolk material in their digestive tracts. The embryonic gut is lined by an epithelium consisting of columnar cells with apical microvilli, providing a means for nutrient absorption. Contrary to statements in the literature, embryos develop minuscule trophotaenial rudiments that extend slightly into the ovarian lumen. These structures are formed of an absorptive epithelium that overlies a vascular stroma, similar to the trophotaeniae of other goodeids. Through late gestation, vitellogenic follicles form and oocytes are discharged into the ovarian lumen, contributing to embryonic nutrition. Thus, histological evidence suggests that embryos chiefly obtain nutrients from ingestion of yolk and maternal secretions released into the ovarian lumen. This function possibly is supplemented by uptake via the small hindgut protrusions and other absorptive surfaces (e.g., the skin and the gill epithelium). Our observations are consistent with two evolutionary interpretations of the hindgut protrusions: (a) that they are rudimentary, evolutionary precursors of trophotaeniae formed by exteriorized hindgut; and (b) that they are vestigial remnants of trophotaeniae that were lost during a switch to a form of matrotrophy involving nutrient ingestion.

Morphology of yolk and pericardial sacs in lecithotrophic and matrotrophic nutrition in poeciliid fishes

We used histological techniques to describe the morphology of the yolk and pericardial sacs in developing embryos of the lecithotrophic species Girardinus creolus, Gambusia puncticulata, Limia vittata, and Quintana atrizona, in comparison with the extreme matrotrophic Heterandria formosa. In lecithotrophic species, the yolk sac was enlarged and lasted until the final stages of development, while in H. formosa it was completely absorbed soon after fertilization. Lecithotrophic poeciliids showed a pericardial sac with a single layer of blood vessels covering the dorsal surface of the cephalic region only, while H. formosa showed a more complex largely vascularized pericardial sac covering the entire dorsal surface, except the caudal region. In advanced gestation of G. creolus, a vascular plexus of the yolk sac reaches the pharyngeal region, behind the gills, suggesting that the pharynx may play a role in embryonic nutrition in lecithotrophic species. These morphological evidences suggest that matrotrophy derives from lecithotrophy.

Structure of the gonoduct of the viviparous teleost Cnesterodon decemmaculatus (Jenyns, 1842) (Poeciliidae)

During embryogenesis, teleost females do not develop Müllerian ducts, which form the oviducts in all other vertebrates. Thus, when they reach sexual maturity they do not have oviducts. In viviparous teleosts, the lack of oviducts means that the development of the embryos occurs as an intraovarian gestation, unique among vertebrates. The ovary is an unpaired hollow organ whose cavity is continuous with the caudal portion, the gonoduct, characterized by the absence of germinal cells, which opens to the exterior at the gonopore. The gonoduct attains essential function as a barrier between the germinal region of the ovary and the exterior during all reproductive stages. This study describes the functional morphology of the gonoduct in the viviparous teleost Cnesterodon decemmaculatus during non-gestation (previtellogenesis and vitellogenesis) and gestation. The ovaries were processed using histological techniques and stained with hematoxylin-eosin, and periodic acid Schiff. The gonoduct has two regions: cephalic and caudal, and is formed by three histological layers, which are, from inside to the periphery: (a) tunica mucosa; (b) tunica muscularis; and (c) tunica serosa. In the cephalic region there are mucosal folds extending into the lumen and forming a structure similar to a cervix. The histology of the gonoduct indicates essential functions, that is, (a) the control of the luminal diameter in the limit to the germinal region of the ovary by the presence of a cervix; (b) during insemination the gonoduct receives the spermatozoa, may store and transport them to the germinal region; (c) the presence of melano-macrophage centers indicates support of immunological processes, especially during gestation when these centers increase in size; (d) production of exocrine secretions; and (e) it is the birth canal, internally lined by an ciliated epithelium and surrounded by smooth musclesboth tissues supposedly supporting the birth process.

Molecular insights into post-mating immune response in a fish with internal fertilization

The tight connection between immunity and reproduction has been studied for decades. However, basic knowledge at the molecular level of the effect of mating on immune function is still lacking in many taxa. Determining whether and how the immune system is engaged after mating is a crucial step in understanding post-mating mechanisms of reproduction and sexual selection. Here, we study the transcriptional changes in immunity-related genes caused by the ejaculate in the female reproductive tract using a model species for sexual selection studies, the guppy Poecilia reticulata. To study changes triggered by the ejaculate only, rather than caused by mating, we used artificial inseminations to transfer ejaculate into females. We then compared gene expression in the reproductive tract (gonoduct and ovary) of females artificially inseminated either with ejaculate or with a control solution, after 1 hr and after 6 hr. Overall, contact with ejaculate caused short-term changes in the expression of immune-related genes in the female reproductive tract, with a complex pattern of up- and down-regulation of immune-related pathways, but with clear indication of a marked down-regulation of the immune system shortly after ejaculate contact. This suggests a link between immune function and processes occurring between mating and fertilization in this species.

Structure of the testis and spermatogenesis of the viviparous teleost Poecilia mexicana (Poeciliidae) from an active sulfur spring cave in Southern Mexico

We describe the histological characteristics of the testis and spermatogenesis of the cave molly Poecilia mexicana, a viviparous teleost inhabiting a sulfur spring cave, Cueva del Azufre, in Tabasco, Southern Mexico. P. mexicana has elongate spermatogonial restricted testes with spermatogonia arranged in the testicular periphery. Germ cell development occurs within spermatocysts. As spermatogenesis proceeds, the spermatocysts move longitudinally from the periphery of the testis to the efferent duct system, where mature spermatozoa are released. The efferent duct system consists of short efferent duct branches connected to a main efferent duct, opened into the genital pore. Spermatogenesis consisted of the following stages: spermatogonia (A and B), spermatocytes (primary and secondary), spermatids, and spermatozoa. The spermatozoa are situated within spermatocysts, with their heads oriented toward the periphery and flagella toward the center. Once in the efferent duct system, mature spermatozoa are packaged as unencapsulated sperm bundles, that is, spermatozeugmata. We suggest that the histological characteristics of the testis and spermatogenesis of P. mexicana from the Cueva del Azufre, and the viviparous condition where the spermatozoa enter in the female without been in the water, have allowed them to invade sulfurous and/or subterranean environments in Southern Mexico, without requiring complex morphofunctional changes in the testis or the spermatogenetic process.

Structures Associated with Oogenesis and Embryonic Development during Intraovarian Gestation in Viviparous Teleosts (Poeciliidae)

Viviparity in teleosts involves, invariably, the ovary in a gestational role. This type of viviparity is due to the combination of unique aspects, different from those found in the rest of vertebrates. These aspects are: The ovary has a saccular structure; the germinal epithelium lines the ovarian lumen; the absence of oviducts; and the intraovarian insemination, fertilization, and gestation. The communication of the germinal zone of the ovary to the exterior is via the caudal zone of the ovary—the gonoduct. The germinal epithelium is composed of oogonia and oocytes scattered individually or in cell nests among somatic epithelial cells. In the ovarian stroma the follicles are included which are formed by the oocyte, which is surrounded by follicular cells and the vascularized theca. The oogenesis comprises three stages: chromatin-nucleolus, previtellogenesis, and vitellogenesis. There is no ovulation, as the oocyte is retained in the follicle. During the insemination, the spermatozoa enter into the ovarian lumen and the intrafollicular fertilization occurs, followed by intrafollicular gestation. The intraovarian gestation of poeciliids involves morphological characteristics associated with the intrafollicular embryogenesis and types of nutrition, such as lecithotrophy and matrotrophy. In lecithotrophy, the nutrients come from the yolk reserves stored during oogenesis, whereas in matrotrophy the nutrients are provided by supplies from maternal tissues to the embryo during gestation. The maternal–embryonic metabolic interchanges converge through the development of the association of maternal and embryonic blood vessels, establishing a follicular placenta.

Directional postcopulatory sexual selection is associated with female sperm storage in Trinidadian guppies

Female sperm storage (FSS) is taxonomically widespread and often associated with intense sperm competition, yet its consequences on postcopulatory sexual selection (PCSS) are poorly known. Theory predicts that FSS will reduce the strength of PCSS, because sperm characteristics favored before and after FSS may be traded-off, and opportunities for nondirectional PCSS should increase. We explored these questions in the guppy (Poecilia reticulata), by allowing females to mate multiply and by comparing the paternity pattern in two successive broods. Contrary to predictions, the variance in male fertilization success increased after FSS, driven by a change in male paternity share across broods. This change was positively associated with sperm velocity (measured before FSS) but not with the duration of FSS, indirectly suggesting that faster sperm were better in entering female storage organs, rather than in persisting within them. Other male traits, such as male size and orange color, heterozygosity, and relatedness to the female, did not influence paternity after FSS. These results indicate that processes associated with FSS tend to reinforce the strength of PCSS in guppies, rather than weaken it. Further work is necessary to test whether this pattern changes in case of more prolonged FSS.