Ovarian changes and development of the branchial placenta occurring in Jenynsia lineata (Cyprinodontiformes, Anablepidae)

In viviparous teleosts, intraovarian gestation occurs intrafollicularly, as in poeciliids, or intraluminally, as in goodeids and anablepids. Furthermore, there are two different forms of embryonic nutrition: lecithotrophy and matrotrophy; depending on the species, these can be exclusive or coexist during gestation. In matrotrophic species, nutrients are transmitted from the mother to the embryo and are especially important in species with intraluminal gestation. Jenynsia lineata is a South American viviparous teleost with intraluminal gestation, characterized by eggs with scarce yolk, which is resorbed when embryos are 6 mm long, thus developing a branchial placenta. Using histological, histochemical, and immunohistochemical techniques, the present study describes the characteristics and changes of the ovarian mucosa in J. lineata during gestational and nongestational phases, and analyzes the embryonic pharyngeal epithelium in the branchial placenta. The ovaries of 30 adult female specimens were processed using histological techniques and stained with hematoxylin-eosin, Masson's trichrome, and Alcian Blue pH 2.5/periodic acid Schiff reagent. To detect cell proliferation, we used antiproliferating cell nuclear antigen antibody. In nonpregnant females, eosinophilic granular cells (EGCs) and lymphocytes were identified in the lamina propria of the tunica mucosa, and melanomacrophage centers (MMCs) and fibroblasts were identified adjacent to tissue debris in the ovarian folds'. In the cellular debris, an embryo in resorption was observed. In pregnant females, the ovarian mucosa has thin vascularization branches entering the opercular chamber of the embryos, in close contact with the forming gill processes, thereby establishing a branchial placenta. Active cell replacement was observed in these ovarian branches. The identification of fibroblasts, lymphocytes, EGCs, and MMCs adjacent to tissue debris could indicate that these cell types are involved in the embryonic resorption process. Considering the new data obtained in this study on the branchial placenta of J. lineata, we conclude that cell proliferation could be involved in the development of maternal-embryonic interaction.

Investigating the Ovarian Microstructure in the Genera Helicolenus and Scorpaena (Teleostei, Sub-Order Scorpaenoidei) with Implications for Ovarian Dynamics and Spawning

Simple Summary

The diversity of reproductive mechanism in bony fishes is greater than in any other group of vertebrates. It ranges from oviparous, to several stages of viviparous forms. In this context, scorpaenoid fishes belonging to the families Scorpaenidae and Sebastidae are of particular interest, since they show extremely varied reproductive modes connected with ovarian structures. We describe here the ovarian morphology of five rockfish species showing different reproductive modalities, using histology. Specialized microscopic features were found during gametogenesis, strictly related to the production of gelatinous mass surrounding the eggs, typical of these species. Based on microscopic maturity stages here analyzed, we found that all species shed eggs more than once through the spawning season, and were characterized by continuous oogenesis with multiple oocyte deposition. Further ovarian dynamic observations supported the hypothesis that all species had an indeterminate fecundity.

Abstract

The sub-order Scorpenoidei appears to be particularly interesting due to the presence of intermediate stages between oviparity and viviparity in several species. The present study aims to describe the ovarian morphology, using a histological and histochemical approach, in four ovuliparous species belonging to Scorpaena genus compared with a zygoparous species, H. dactylopterus, focusing also on the assessment of the ovarian dynamics in the populations of such species in Sardinia waters (central–western Mediterranean). Ovarian sections of all species were examined using light microscopy. All species showed a specialized ovary, cystovarian type II-3, strictly related to the production of gelatinous matrices surrounding the eggs. Some microscopic peculiarities in the oogenesis process were found: thin zona pellucida, small and low cortical alveoli, and a specialized ovarian wall during the spawning period. All species analyzed were batch-spawners with an asynchronous ovarian organization. A continuous recruitment of oocytes and the occurrence of de novo vitellogenesis was also observed. During the spawning period, low atresia intensity was detected, while a marked increase in this intensity found in the ovaries at the end of spawning season. Our observations may support an indeterminate fecundity type for these species.

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.

Sperm maturation, migration, and localization before and after copulation in black rockfish (Sebastes schlegelii)

Sebastes schlegelii is a typical viviparous teleost with six months sperm storage duration from November to April. In this study, spermatozoa morphological and physiological characteristics and sperm location in the female ovary were investigated by electron microscopy, computer-assisted sperm analyzer and histologic analysis, respectively. During copulation, we observed that spermatozoa in the testis had mature structure with rod-shaped head, a short midpiece, and a long flagellum. And further verified sperm swam freely at a high speed in the ovary fluid. After copulation, we only found swimming sperm in the ovary fluid at the early storage stage (November to December) and the majority of sperm were scattered randomly in the ovary cavity and partially concentrated in the crypt between the oocyte and stalk of follicle. Thereafter, the ovarian epithelium around the oocytes proliferated rapidly and wrapping spermatozoa outside of the follicular layer and formed a lot of crypts outside of the follicular layer which served as the sperm storage site until fertilization. The present findings would be useful for further understanding the mechanism of long-term sperm storage in viviparous teleost.

Spermatozoon and its relationship with the ovarian lamellae in the internally inseminating catfish Trachelyopterus galeatus

We examined the spermatozoa and their relationship with the ovarian lamellae in the catfish Trachelyopterus galeatus by classical light microscopy, high-resolution light microscopy, and transmission electron microscopy. Trachelyopterus galeatus is an internally inseminating species the spermatozoon of which presented an elongated cylindrical head (12.3 +/- 1.5 microm), elongated midpiece (5.0 +/- 0.7 microm), and flagellum (23.9 +/- 2.8 microm). Fertilized eggs or embryos were not found in its ovaries. Spermatozeugmata were demonstrated for the first time in this species. At the ultrastructural level, the anterior region of the head was devoid of chromatin with its shape being rounded with a hyaline tip in frontal sections and flattened in sagittal sections. The proximal centriole and most of the distal centriole were contained within a nuclear fossa. Mitochondria with lamellar cristae, as well as glycogen granules, were located just caudal to the nuclear fossa and distally in the midpiece. A single row of accessory microtubules ran peripherally in the midpiece. The flagellar axoneme had the typical 9 + 2 arrangement, having electron-dense and electron-lucent A-tubules at different points along the flagellum; flagellar fins were lacking. The ovarian lamellae were covered by a simple cuboidal epithelium. In maturing/mature females, spermatozoa were free in the ovarian lumen or inserted in pits of the lamellar epithelial cells. Tight junctions and desmosomes were seen between the epithelial cells. In addition to nourishment of the spermatozoon, the lamellar epithelial cells may play a role in protecting the spermatozoa against the female immune system.

Sperm storage and motility in the ovary of the marine sculpin Alcichthys alcicornis (Teleostei: Scorpaeniformes), with internal gametic association

Elkhorn sculpin, Alcichthys alcicornis, is a marine teleost with a unique reproductive mode called "internal gametic association," in which sperm introduced into the ovary by copulation enter the micropylar canal of ovulated eggs in the ovarian cavity, but actual sperm-egg fusion does not occur until the eggs have been released into sea water. It is also known that this fish is a multiple spawner, which spawns at intervals of a few days for one month, and the sperm introduced into the ovary at the beginning of the spawning season retain their fertilizability for the entire period. To clarify how the fertilizability of sperm is maintained internally, the ultrastructure of sperm, the morphological characteristics related to sperm storage in the ovary, and the characteristics of sperm motility were investigated. Mature sperm generally have the normal form of teleost sperm, devoid of acrosomal structures. However, it was found that the midpiece is comparatively elongated and has a compact aggregation of many small-size mitochondria. The intraovarian sperm remained floating in the ovarian fluid throughout the spawning season. The sperm showed high motility in isotonic and weak alkaline solution, containing sodium ions, which was similar to the ovarian fluid of this fish. Sperm continued to move in artificial ovarian fluid for 7-14 days. Considering these results together, it is thought that the intraovarian sperm move throughout the spawning season due to the plentiful energy generated by the many mitochondria.

Histochemical analysis of sperm storage in Helicolenus dactylopterus dactylopterus (Teleostei: Scorpaenidae)

The bluemouth rockfish, Helicolenus dactylopterus dactylopterus (De la Roche, 1809), is a zygoparous species with internal fertilization. The male urogenital papilla acts as the copulating organ, and the females retain the spermatozoa in their ovaries for up to 10 months. The objective of this study is to extend our knowledge of the mechanisms that allow the sperm to be retained in the ovaries for prolonged periods. To this end, we analyze the histochemical properties of: 1) the epithelium of the testicular sperm duct, 2) the sperm of the males, 3) the internal epithelium of the ovary wall, 4) the ovarian fluid, and 5) the spermatozoa storage crypts of females. The PAS (Periodic acid-Schiff) and bright Coomassie blue positive reactions of the epithelium of the spermatic duct point to the secretion of polysaccharides and proteins that could promote the bundling of the spermatozoa. The internal epithelium of the ovarian wall secretes polysaccharides, protein, and lipid compounds throughout the storage and spawning period. The acid nature of the ovarian fluid during the storage period may maintain the bundling of spermatozoa when they enter the ovary and may also inhibit sperm motility until the moment of fertilization. The polysaccharide granules that come from the cryptal epithelium into the cavity where spermatozoa are maintained may supply them with nutrients for the storage period. The presence of glucosaminoglycans on the surface of the sperm is probably related to the inhibition of spermatic motility produced by the acidic environment. They are absent in the spermatozoa located in the testicular ducts, relatively scarce in those of the duct of the copulating organ, and abundant in those within the intraovarian cryptal structures.

Ultrastructural observations on sperm storage in the ovary of the platyfish, Xiphophorus maculatus (Teleostei: poeciliidae): the role of the duct epithelium

Sperm storage is an important phenomenon occurring in viviparous and oviparous teleosts and contributes to the reproductive life history of these forms. There is a paucity of morphological studies on sperm storage in fishes. The majority of these have been confined to the light level of investigation. In this report, we describe, at the ultrastructural level, sperm storage in the viviparous platyfish, Xiphophorus maculatus. Female platyfish, as is typical of the poeciliids, are capable of storing viable sperm for up to several months within the ovary and gonoduct. We observed that sperm stored within inseminated platyfish became associated with specific epithelial cells (SACs) lining the oviduct. Two forms of association were seen: 1) sperm were found within deep surface pits and pockets, and 2) the spermatozoa were taken up and incorporated within the cytoplasm of the SACs. Junctional complexes in the form of tight junctions (zona occludens) and desmosomes at the apico-lateral surfaces of the SACs were prevalent. The junctions could have contributed to allograft survival of the haploid heterogenetic sperm cells within the female's reproductive tract. Our results shed light on the mechanism of sperm storage in the platyfish and could serve as a model for other poeciliid species and teleosts that are capable of storing sperm.