Realistic nitrate concentrations diminish reproductive indicators in , an endemic species in critical endangered status.

Goodeinae is a subfamily of critically endangered fish native to central Mexico. Populations of , a species belonging to this subfamily, have significantly decreased in the past two decades. A previous study showed that is sensitive to acute nitrate-nitrogen (NO-N) exposure, leading to noticeable changes in both behavioral and histopathological bioindicators.

Histological characteristics of oocyte differentiation in the captive longnose seahorse Hippocampus trimaculatus (Leach, 1814).

This study aimed to explore the reproductive histology and oocyte differentiation of the longnose seahorse Hippocampus trimaculatus (Leach, 1814) in captivity. Five mature healthy females were histologically observed. The reproductive systems of the five specimens exhibited similar morphological characteristics with a pair of saccular creamy white ovaries merging caudally into a single gonoduct.

The male reproductive cycle of the brown basilisk Basiliscus vittatus (Squamata: Corytophanidae) from Tabasco, Southern Mexico.

We used histological and morphometric methods to study the testis and associated glands, including the epididymis, ductus deferens, and renal sexual segment (RSS), of specimens of Basiliscus vittatus sampled from Tabasco, Mexico (17.5926° N, 92.5816° W).

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.

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.

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.

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.

Morphological patterns of cell death in ovarian follicles of primary and secondary growth and postovulatory follicle complex of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae).

The dynamics of cellular development and homeostasis of the ovary depend on the balance between proliferation and cell death throughout the reproductive cycle. Millerichthys robustus is an annual fish whose ovarian follicles develop asynchronously, allowing daily reproduction from sexual maturity until death. The objective of this research is to describe, histologically, the processes of follicular atresia and regression of postovulatory follicular complexes (POC) throughout a reproductive cycle of M.

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.

Superfetation in the viviparous fish Heterandria formosa (Poeciliidae).

Heterandria formosa is a viviparous poeciliid native of the southeastern of United States of America. H. formosa exhibits unique reproductive features as: (a) production of extremely small eggs with scarce quantity of yolk (microlecithal eggs), (b) consequently, a high level of matrotrophy and development of a complex follicular placenta, (c) ovarian sperm storage that allows the continuous fertilization of oocytes and production of offspring and (d) development of high degree of superfetation.

Ovarian structure, folliculogenesis and oogenesis of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae).

Cellular aspects of oocyte development of the Mexican rivulus Millerichthys robustus were morphologically described in order to analyze ovarian function and the cellular recruitment dynamics associating it with life history strategies of annual killifishes. Millerichthys is an iteroparous batch spawner with continuous oocyte recruitment and indeterminate fecundity with asynchronous development of the follicles. It has two ovaries of cystovarian type, with a central lumen, which communicates with the outside through the caudal region of the ovary, that is, the gonoduct.

Testicular structure and spermatogenesis of the oviparous goodeids Crenichthys baileyi (Gilbert, 1893) and Empetrichthys latos Miller, 1948 (Teleostei, Cyprinodontiformes).

The cyprinodontiform family Goodeidae comprises some 51 species, including subspecies, of freshwater fishes all of which are at risk or are extinct in the wild. It is classified in two allopatric subfamilies: the Goodeinae, endemic to the Mexican Plateau, and the Empetrichthyinae, known only from relict taxa in Nevada and southern California. The 41 species of goodeins are all viviparous and share a set of well-documented reproductive characters.

Change of lecithotrophic to matrotrophic nutrition during gestation in the viviparous teleost Xenotoca eiseni (Goodeidae).

Teleosts possess unique features of the female reproductive system compared with the rest of vertebrates, features that define the characteristics of their viviparity. Viviparity involves new maternal-embryonic relationships detailing the most diverse structures during gestation that include embryonic nutrition. In order to analyze the morphological features of the complex nutrition in viviparous teleosts during intraovarian gestation, this study utilizes the goodeid Xenotoca eiseni as a model.

Insemination, intrafollicular fertilization and development of the fertilization plug during gestation in Heterandria formosa (Poeciliidae).

The viviparous teleost Heterandria formosa is a remarkable species for its reproductive characters including: (a) the smallest oocyte in viviparous fish species; (b) a high level of matrotrophy with a complex placenta; and (c) the highest level of superfetation. Superfetation involves (d) the continuous development of oocytes and fertilization at the same time with embryos in gestation. The sequential fertilization of oocytes requires (e) storage of spermatozoa in the ovary.

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.

Ovarian structure and oogenesis of the extremophile viviparous teleost Poecilia mexicana (Poeciliidae) from an active sulfur spring cave in Southern Mexico.

The structure of the ovary and oogenesis of Poecilia mexicana from an active sulfur spring cave is documented. Poecilia mexicana is the only poeciliid adapted to a subterranean environment with high hydrogen sulfide levels and extreme hypoxic conditions. Twenty females were captured throughout one year at Cueva del Azufre, located in the State of Tabasco in Southern Mexico.

Permanent germinal epithelium and reproductive cycle of Atractosteus tropicus (Lepisosteiformes: Lepisosteidae) males, Tabasco, Mexico.

The tropical gar A. tropicus plays an important ecological role as it regulates other fish stocks in different water bodies in Southeastern México. Nevertheless, wild populations are declining, and one conservation alternative is the aquaculture production and basic knowledge of reproductive biology; for males, this requires the study of germ and somatic structures of testes, to characterize the reproductive cycle, and to provide basic knowledge for exploitation and conservation models and strategies.

Oogenesis: From Oogonia to Ovulation in the Flagfish, Jordanella floridae Goode and Bean, 1879 (Teleostei: Cyprinodontidae).

We provide histological details of the development of oocytes in the cyprinodontid flagfish, Jordanella floridae. There are six stages of oogenesis: Oogonial proliferation, chromatin nucleolus, primary growth (previtellogenesis [PG]), secondary growth (vitellogenesis), oocyte maturation and ovulation. The ovarian lamellae are lined by a germinal epithelium composed of epithelial cells and scattered oogonia.

Morphological development of the structures related to annualism in the ovarian follicle of the killifish Millerichthys robustus (Costa,1995) (Teleostei: Cyprinodontiformes).

Ovaries of five females of the annual fish teleost species Millerichthys robustus were processed, and the development of the cortical alveoli, zona pellucida and secondary envelope during oogenesis were described. We also documented the origin of the cortical alveoli in time and space similar to the Balbiani body; the synthesis of three generations of cortical alveoli and an active zona pellucida prior to vitellogenesis, which is implicated in the entry of oils to the interior of the oocyte. We found that in this species, the diameter of the alveoli is greater than in the other teleost fish species reported in the literature, except for Fundulus heteroclitus, in which the diameter is similar.

Conserved form and function of the germinal epithelium through 500 million years of vertebrate evolution.

The germinal epithelium, i.e., the site of germ cell production in males and females, has maintained a constant form and function throughout 500 million years of vertebrate evolution.

The occurrence of spermatozoa in the ovary of the gynogenetic viviparous teleost Poecilia formosa (POECILIIDAE).

The reproductive mode of the female viviparous teleost Poecilia formosa (Poeciliidae) represents the phenomenon known as gynogenesis; that is, parthenogenetic development is initiated by spermatozoa which are needed for physiological activation of the egg and the initiation of gestation, but spermatozoa are prevented from contributing to the genome of the embryo. For the reason that no previous histological analyses of the ovary of this species during the reproductive cycle has been published the present study has been conducted. This study examined the histology of the ovary of P.

Testicular structure and germ cells morphology in salamanders.

Testes of salamanders or urodeles are paired elongated organs that are attached to the dorsal wall of the body by a mesorchium. The testes are composed of one or several lobes. Each lobe is morphologically and functionally a similar testicular unit.

Comparative testicular structure and spermatogenesis in bony fishes.

In most bony fishes, testes are paired elongated organs that are attached to the dorsal wall of the body by a mesorchium. Histological examination of teleost testes, and also in all vertebrates, shows that the testes are formed of germ cells and somatic cells, comprising the germinal and interstitial compartments. Both compartments are separated by a basement membrane.

Branchial placenta in the viviparous teleost Ilyodon whitei (Goodeidae).

Intraluminal gestation, as it occurs in viviparous goodeids, allows a wide diversity of embryo-maternal metabolic exchanges. The branchial placenta occurs in embryos developing in intraluminal gestation when ovarian folds enter through the operculum, into the branchial chamber. The maternal ovarian folds may extend to the embryonic pharyngeal cavity.

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.