Embryonic development of the fire-eye-tetra Moenkhausia oligolepis (Characiformes: Characidae).

This study describes the embryonic development of Moenkhausia oligolepis in laboratory conditions. After fertilization, the embryos were collected every 10 min up to 2 h, then every 20 min up to 4 h, and afterwards every 30 min until hatching. The fertilized eggs of M. oligolepis measured approximately 0.85 ± 0.5 mm and had an adhesive surface. Embryonic development lasted 14 h at 25ºC through the zygote, cleavage, blastula, gastrula, neurula, and segmentation phases. Hatching occurred in embryos around the 30-somites stage. The present results contribute only the second description of embryonic development to a species from the Moenkhausia genus, being also the first for this species. Such data are of paramount importance considering the current conflicting state of this genus phylogenetic classification and may help taxonomic studies. Understanding the biology of a species that is easily managed in laboratory conditions and has an ornamental appeal may assist studies in its reproduction to both supply the aquarium market and help the species conservation in nature. Moreover, these data enable the use of M. oligolepis as a model species in biotechnological applications, such as the germ cell transplantation approach.

Reproductive cycle of the tetra Astyanax bimaculatus (Characiformes: Characidae) collected in Amazonian streams.

A histological characterization of gonadal development in the tetra Astyanax bimaculatus was performed, aimed at determining its reproductive cycle in streams localized inside the Amazonian forest. Collections were carried out monthly from August 2017 to July 2018 at the Zoobotânica Foundation of Marabá, PA. Collected specimens were weighed and measured, and their gonads and liver were removed and weighed to calculate gonadosomatic and hepatosomatic indexes. Gonads were fixed and treated for routine histology for light microscopy. Materials were stained with toluidine blue and haematoxylin and eosin. The Amazonian A. bimaculatus species presented two reproductive periods in the year, one at the end of the winter season and another during the summer. Females showed an asynchronous development of their oocytes and only two reproductive phases of development were observed during the whole period 'developing' and 'spawning capable'. Males presented cystic spermatogenesis, with an anastomosing tubular testis containing spermatogonia spread along the germinal epithelium (unrestricted spermatogonial). These morphological characteristics are considered phylogenetically more primitive. Male specimens were observed to have five different phases during the period: immature, initial maturation, mid maturation, final maturation and regression. The huge fluctuations in Amazonian streams was observed, in which water volumes varied considerably across seasons, culminating even in total drought. In spite of this, A. bimaculatus could be found during all seasons, showing its impressive reproductive adaptation to its conditions.

First report of complete albinism in Mazama americana (Erxleben, 1777) in the Biological Reserve of Tapirapé, Oriental Amazon, Brazil

Albinism is a genetic condition that results in total hypopigmentation of the eyes, fur, skin, hair, scales, and feathers of an organism. Albinism might result in a selective disadvantage for affected animals. Cases of albinism have been previously recorded in Neotropical vertebrates, such as reptiles, mammals, birds, and fish. However, observing albinism in a wild population is still considered to be a rare event. This paper reports a unique case of complete albinism in a red-brocket deer (Mazama americana) living in the Brazilian Amazon rainforest. The individual was observed within the Biological Reserve of Pará State, one of the most deforested regions of the Brazilian Amazon. The survival of the albino red-brocket deer in the wild can be related to mechanisms of apostatic selection, which theorize the survival of individual prey animals whose mutations make them less likely to be attacked by predators. In other words, the more different a prey animal is from others, the less likely it will be targeted by predators. The high abundance prey animals within the Biological Reserve of Tapirapé seems to support this prediction. This report exemplifies the importance of monitoring the biodiversity and promoting the conservation of favorable habitats to support species multiplicity in highly fragmented regions, as in the Brazilian Amazon.

Morphological evaluation of Prochilodus lineatus embryos after vitrification-thawing in high-osmolarity cryoprotectant solution.

We aimed to vitrify embryos of Prochilodus lineatus in a high-osmolarity cryoprotectant solution, evaluating, after the vitrification-thawing process, their morphological changes. Thus, 240 embryos in the 20-somite phase (20S) were exposed for 20 min to one main internal cryoprotectant solution (1,2-propanediol-PROP), divided into four immersion sequence steps of five minutes each. The first three steps were performed in solutions containing only a main internal cryoprotectant (PROP-2, 3 and 4 M), and the fourth step in a high-osmolarity solution combining internal (PROP + dimethyl sulphoxide-Me2 SO) and external cryoprotectants (sucrose-SUC). The final concentration of vitrification was PROP 5 M + Me2 SO 5 M + SUC 0.2 M. During vitrification, the straws exhibited a translucent solid appearance; however, during thawing, their structure became totally opaque and white. After thawing, the embryos suffered an increase in volume and presented morphological changes including protrusions on the surface of the yolk sac, yolk sac rupture, and optical vesicle degradation. On the inside, we observed intercellular spaces and a yolk syncytial layer (YSL) with altered chromatin. Yet, structures such as somites, neural tube, endoderm and epidermis presented cells with a nucleus and integral mitochondria. We conclude that the use of the tested cryoprotectant solution permits the formation of a vitreous solid and preserves part of the cells of the blastoderm. Yet, the heating protocol does not control recrystallization, resulting in the formation of serious morphological anomalies that prevent the preservation of the embryonic unit.

Behavioral and biochemical effects of ethanol withdrawal in zebrafish.

Chronic alcohol use induces adaptations and toxicity that can induce symptoms of anxiety, autonomic hyperarousal, and epileptic seizures when alcohol is removed (withdrawal syndrome). Zebrafish has recently gained wide attention as a behavioral model to study the neurobehavioral effects of acute and chronic alcohol use, including withdrawal. The literature, however, is very contradictory on findings regarding withdrawal effects, with some studies reporting increased anxiety, while others report no effect. A meta-analytic approach was taken to find the sources of this heterogeneity, and ethanol concentration during exposure and exposure duration were found to be the main sources of variation. A conceptual replication was also made using continuous exposure for 16 days in waterborne ethanol (0.5%) and assessing anxiety-like behavior in the light/dark test after 60 min withdrawal. Withdrawal was shown to reduce preference for darkness, consistent with decreased anxiety, but to increase risk assessment, consistent with increased anxiety. Animals were also subjected to the withdrawal protocol and injected with pilocarpine in a sub-convulsive dose to assess susceptibility to epileptic seizure-like behavior. The protocol was sufficient to increase susceptibility to epileptic seizure-like behavior in animals exposed to ethanol. Finally, withdrawal also decreased catalase activity in the brain, but not in the head kidney, suggesting mechanisms associated with the behavioral effects of ethanol withdrawal.

The efficiency of spermatogenesis and the support capacity of Sertoli cells in Characiformes.

This stereological analysis of the types of germ cells and the number of Sertoli cells per cyst in Astyanax altiparanae testes during spermatogenesis is the first such report in Characiformes. Testes of 25 male A. altiparanae were examined. Based on the number of spermatogonia B per cyst (469.2 ± 9.92), we estimated that spermatogonia undergo at least nine mitotic divisions before differentiating into primary spermatocytes. There are four spermatogonia types: undifferentiated spermatogonia A*, undifferentiated spermatogonia, differentiated spermatogonia, and type B spermatogonia. The number of Sertoli cells increased gradually from 1.41 ± 0.51 in the single undifferentiated spermatogonium A* to 9.25 ± 0.50 in cysts of spermatocytes in the leptotene/zygotene stage, possibly related to greater complexity of cellular events during the meiotic stage. The number of germ cells rose dramatically from spermatogonia A (1.0 ± 0) to spermatogonia B (469.2 ± 9.92); however, the quantity of spermatocytes inside the cysts in the leptotene/zygotene stage decreased (300.6 ± 6.97) relative to spermatogonia B, representing a loss of approximately 36% of the former number of cells. This was probably the result of apoptosis, which promotes successful development of the remaining cells during sperm production. The support capacity of Sertoli cells increased gradually during spermatogenesis.

Morphology of the urogenital papilla and its component ducts in Astyanax altiparanae Garutti & Britski, 2000 (Characiformes: Characidae)

The histological description of the urogenital papilla is an important tool to comprehension of the reproductive mechanisms in fish, as well as a pre-requisite to germ cell transplantation in adult fish, besides to be a good biological indicator to environmental changes. Was performed the histological description of the urogenital papilla and its component ducts in the tetra Astyanax altiparanae. The genital and urinay ducts pass separately throughout most part of its extension, joining in a single duct before opening. In males this opening is asymmetric and seems to have double origin, being completely surrounded by striated muscle fibers, while in females it is symmetric and the muscle fibers does not surround it totally. Spermatic duct and oviduct undergo changes throughout their extension, mainly in the morphology of the surrounding epithelium. In the spermatic duct, squamous epithelial cells change to columnar and cuboid with possible secretory activity, close to testes. In the oviduct, anteriorly epithelial cells are also squamous, however, close to ovary there are lamellae composed by a pseudostratified epithelium with columnar and cuboid cells. The urinary duct is highly similar for both sexes presenting globoid cells, which description is known in mammals, however, rare in fish.

A descrição histológica da papila urogenital é uma importante ferramenta para a compreensão dos mecanismos reprodutivos em peixes, assim como um pré-requisito para a realização do transplante de células germinativas em peixes adultos, além de um bom indicador biológico de possíveis alterações ambientais. Foi realizada a investigação histológica da papila urogenital e seus ductos constituintes no lambari Astyanax altiparanae. Os ductos genital e urinário ocorrem separadamente ao longo de maior parte de sua extensão, entretanto, unem-se em um ducto simples antes de abrir para o meio externo. Nos machos esta abertura é assimétrica e parece ter dupla origem, sendo completamente envolvida por fibras musculares estriadas, enquanto nas fêmeas ela é simétrica e as fibras musculares não a envolve totalmente. O ducto espermático e oviducto sofrem alterações ao longo de sua extensão, principalmente na morfologia do epitélio que os envolve. No ducto espermático as células epiteliais passam de pavimentosas a colunares e cuboides, com possível atividade secretora, à medida que se aproxima dos testículos. No oviducto, anteriormente as células também são epiteliais pavimentosas, entretanto, próximo aos ovários, formam-se lamelas compostas por um epitélio pseudoestratificado composto por células cuboides e colunares. O ducto urinário é bastante similar em ambos os sexos apresentando células globosas, cuja descrição é conhecida em mamíferos, porém rara em peixes.

Reproductive cycle of the neotropical cichlid yellow peacock bass cichla kelberi: a novel pattern of testicular development

The present study describes the testicular maturation phases (associating the germ cells development and the morphological changes suffered by the germinal epithelium along the whole year), and the testicular morphology in the yellow peacock bass Cichla kelberi, relating it to other species. For this purpose, 78 specimens were studied according conventional techniques of light microscope. The testes in C. kelberi were classified as unrestricted spermatogonial lobular, an apomorphic characteristic in the recent groups of Teleost. Furthermore, were defined five testicular maturation phases: Preparatory phase; Early Germinal Epithelium Development; Mid Germinal Epithelium Development; Late Germinal Epithelium Development and; Regression. Similar classifications were described to other species indicating that the testicular classifications based on this propose, can be applied to lots of fishes. However, besides it similarity, the testicular reproductive cycle of C. kelberi follows a different pattern in the Regression phase, on which the gonadal restructuration and the spermatogonial proliferation gathers at the same time. So, the testes in C. kelberi never return to the Preparatory phase to start a new reproductive cycle, being this one present only at the first reproductive cycle in this species. This fact also explains the absence of individuals totally spent after their first reproductive cycle.

O presente estudo descreve as fases de maturação testicular (associando o desenvolvimento das células germinativas e as alterações morfológicas sofridas pelo epitélio germinativo ao longo do ano), e a morfologia testicular do tucunaré amarelo Cichla kelberi, relacionando a outras espécies. Com este propósito, 78 indivíduos foram estudados de acordo com técnicas convencionais para microscopia de luz. Os testículos em C. kelberi foram classificados como lobular espermatogonial irrestrito, uma característica apomórfica encontrada nos grupos recentes dos teleósteos. Além disso, cinco fases de maturação testicular foram definidas para C. kelberi: Fase Preparatória; Desenvolvimento Inicial do epitélio germinativo; Desenvolvimento Intermediário do epitélio; Desenvolvimento Final do epitélio germinativo e Regressão. Classificações similares foram descritas para outras espécies, indicando que a classificação gonadal baseada nesta proposta, pode ser aplicada a muitas espécies de peixes. Entretanto, apesar desta similaridade, o ciclo reprodutivo testicular de C. kelberi segue um padrão diferente na fase de Regressão, na qual a reestruturação gonadal e a proliferação espermatogonial ocorrem ao mesmo tempo. Deste modo, os testículos em C. kelberi nunca retornam à fase Preparatória para começar um novo ciclo reprodutivo nesta espécie. Este fato também explica a ausência de indivíduos totalmente esgotados após seu primeiro ciclo reprodutivo.