Oogenesis in the lizard Mabuya brachypoda is seasonal, with oogenesis initiated during May-June and ovulation occurring during July-August. This species ovulates an egg that is microlecithal, having very small yolk stores. The preovulatory oocyte attains a maximum diameter of 0.9-1.3 mm. Two elongated germinal beds, formed by germinal epithelia containing oogonia, early oocytes, and somatic cells, are found on the dorsal surface of each ovary. Although microlecithal eggs are ovulated in this species, oogenesis is characterized by both previtellogenic and vitellogenic stages. During early previtellogenesis, the nucleus of the oocyte contains lampbrush chromosomes, whereas the ooplasm stains lightly with a perinuclear yolk nucleus. During late previtellogenesis the ooplasm displays basophilic staining with fine granular material composed of irregularly distributed bundles of thin fibers. A well-defined zona pellucida is also observed. The granulosa, initially composed of a single layer of squamous cells during early previtellogenesis, becomes multilayered and polymorphic. As with other squamate reptiles, the granulosa at this stage is formed by three cell types: small, intermediate, and large or pyriform cells. As vitellogenesis progresses the oocyte displays abundant vacuoles and small, but scarce, yolk platelets at the periphery of the oocyte. The zona pellucida attains its maximum thickness during late oogenesis, a period when the granulosa is again reduced to a single layer of squamous cells. The vitellogenic process observed in M. brachypoda corresponds with the earliest vitellogenic stages seen in other viviparous lizard species with larger oocytes. The various species of the genus Mabuya provided us with important models to understand a major transition in the evolution of viviparity, the development of a microlecithal egg.
We describe seasonal variations of the histology of the seminiferous tubules and efferent ducts of the tropical, viviparous skink, Mabuya brachypoda, throughout the year. The specimens were collected monthly, in Nacajuca, Tabasco state, Mexico. The results revealed strong annual variations in testicular volume, stages of the germ cells, and diameter and height of the epithelia of seminiferous tubules and efferent ducts. Recrudescence was detected from November to December, when initial mitotic activity of spermatogonia in the seminiferous tubules were observed, coinciding with the decrease of temperature, photoperiod and rainy season. From January to February, early spermatogenesis continued and early primary and secondary spermatocytes were developing within the seminiferous epithelium. From March through April, numerous spermatids in metamorphosis were observed. Spermiogenesis was completed from May through July, which coincided with an increase in temperature, photoperiod, and rainfall. Regression occurred from August through September when testicular volume and spermatogenic activity decreased. During this time, the seminiferous epithelium decreased in thickness, and germ cell recruitment ceased, only Sertoli cells and spermatogonia were present in the epithelium. Throughout testicular regression spermatocytes and spermatids disappeared and the presence of cellular debris, and scattered spermatozoa were observed in the lumen. The regressed testes presented the total suspension of spermatogenesis. During October, the seminiferous tubules contained only spermatogonia and Sertoli cells, and the size of the lumen was reduced, giving the appearance that it was occluded. In concert with testis development, the efferent ducts were packed with spermatozoa from May through August. The epididymis was devoid of spermatozoa by September. M. brachypoda exhibited a prenuptial pattern, in which spermatogenesis preceded the mating season. The seasonal cycle variations of spermatogenesis in M. brachypoda are the result of a single extended spermiation event, which is characteristic of reptilian species.
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. Ovaries were processed with histological techniques. P. mexicana has a single, ovoid ovary with ovigerous lamella that project to the ovarian lumen. The ovarian wall presents abundant loose connective tissue, numerous melanomacrophage centers and large blood vessels, possibly associated with hypoxic conditions. The germinal epithelium bordering the ovarian lumen contains somatic and germ cells forming cell nests projecting into the stroma. P. mexicana stores sperm in ovarian folds associated with follicles at different developmental phases. Oogenesis in P. mexicana consisted of the following stages: (i) oogonial proliferation, (ii) chromatin nucleolus, (iii) primary growth, subdivided into: (a) one nucleolus, (b) multiple nucleoli, (c) droplet oils-cortical alveoli steps; (iv) secondary growth, subdivided in: (a) early secondary growth, (b) late secondary growth, and (c) full grown. Follicular atresia was present in all stages of follicular development; it was characterized by oocyte degeneration, where follicle cells hypertrophy and differentiate in phagocytes. The ovary and oogenesis are similar to these seen in other poeciliids, but we found frequent atretic follicles, melanomacrophage centers, reduced fecundity and increased of offspring size.
El robalo blanco Centropomus undecimalis es un pez protándrico hermafrodita con un alto valor comercial y potencial de cultivo en México y Estados Unidos de América, y en Centroamérica y el Caribe es sustento importante de su pesca artesanal. Diversos estudios indican que las hembras aparentemente presentan un mayor crecimiento que los machos. El objetivo del presente estudio consistió en evaluar el efecto de la suplementación del esteroide 17-β estradiol (E2) en el alimento sobre la proporción de sexos de esta especie bajo condiciones de laboratorio. Para ello se realizó un estudio donde se evaluaron seis tratamientos (tiempos de exposición) con 17-β estradiol (7, 14, 21, 28, 35 y 42 días) usando alimento impregnado con 50 mg kg-1 de 17-β estradiol y una dieta control sin esteroide.Después de los días de exposición, los peces fueron mantenidos con dieta sin 17-β estradiol hasta completar 204 días de crianza, determinándose la proporción de sexos, crecimiento y supervivencia. Al final del período de crianza, los peces alimentados con dieta enriquecida con 17-β estradiol por 21 y hasta 42 días muestran la mayor proporción de hembras (93%), mientras que el grupo control presentó el 100% de machos. El mayor crecimiento en longitud y peso se obtuvo en los peces alimentados por 21 días con el E2 (193.11 ± 1.83 mm y 28.56 ± 0.63 g) comparado con el resto. La supervivencia no mostró diferencias significativas entre los tratamientos (92% a 98%). Se concluye que es posible obtener altos porcentajes de feminización utilizando 17-β estradiol al alimentar a los peces por al menos 21 días. Abstract Common snook Centropomus undecimalis is a protandric fish with a high commercial importance and aquacultural potential in Mexico and the United States. Several studies indicate that females have higher growth capacity than males. For this reason, the objective of this research was to evaluate the effect of a 17β-estradiol (E2) diet supplementation on sex proportion for this species. In this sense, an experimental study was conducted where fish were fed for different time periods (7, 14, 21, 28, 35, and 42 days) with food impregnated with 50 mg of E2/Kg, and one control diet without the presence of the steroid. After feeding times, fish were raised for additional 204 days with the control diet to evaluate sex proportion, growth and survival. Our results showed that fish fed with E2 for 21 days or more had the highest female sex proportion (93-100%), while the control group showed the highest male proportion (100%). The highest growth (weight and total length) was detected in fish fed with E2 for 21 days (193.11 ± 1.83 mm and 28.56 ± 0.63 g) compared with the rest of the treatments. Survival did not show statistical differences between treatments (92-98%). We conclude that high percentage of C. undecimalis females can be obtained when fish are fed for 21 days or more with artificial food supplemented with E2.
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