In this study, we describe for the first time the details of the pituitary gland morphogenesis and the ontogeny of adenohypophyseal cells of a South American Characiform species with great importance for Brazilian Aquaculture, Salminus brasiliensis (Characiformes, Characidae), from hatching to 25 days after hatching (dah), by histochemical and immunocytochemical methods. The pituitary placode was first detected at hatching (0 dah), and the pituitary anlage became more defined at 0.5 dah. The neurohypophysis (NH) development started at 3 dah, and the early formation of its stalk at 12.5 dah. An increase in adenohypophyseal and NH tissues was also observed, and in juveniles at 25 dah, the pituitary displayed similar morphology to that found in adults of this species, displaying the main features of the teleost pituitary. PRL cells were detected at 0.5 dah, together with ACTH and α-MSH cells, followed by GH and SL cells at 1.5 dah. β-FSH cells were detected at 25 dah, while β-LH cells at 5 dah. The pituitary development in this species comprises a dynamic process similar to other teleosts. Our findings in S. brasiliensis corroborate the heterogeneity in the ontogeny of adenohypophyseal cells in teleosts and suggest a role for adenohypophyseal hormones in the early development of this species.

Captive reproduction is one of the problems faced in aquaculture requiring the manipulation of environmental factors and/ or hormonal treatment. Thus, we seek to verify experimentally which gonadal changes were present in mature individuals of Astyanax altiparanae arising from decreased water level. Collections were made every four hours, initiated four hours before and finished 28 hours after stimulation, at the Fish Farming Station of Companhia Energética de São Paulo, São Paulo, Brazil. The gonads were analyzed by light microscopy. The females had ovaries in the spawning capable phase until 12h; in 16h, in a more advanced stage of spawning capable phase; and, from 20h, in the regressing phase. Males had testes in the spawning capable phase until 8h; in 12h, in a more advanced stage of spawning capable phase; and, from 16h, the return to the spawning capable phase. The morphological description was corroborated by the proportion of cell classes. Females presented variation on the gonadosomatic index, but it was not found an emptying of the gonad for neither sex. The process of inducing reproduction with water level drawdown was considered satisfactory, since both sexes presented a reduction in the number of mature gametes at the end of the sample period.Reprodução em cativeiro é um dos problemas enfrentados na aquicultura exigindo a manipulação de fatores ambientais e/ ou tratamento hormonal. Assim, verificou-se experimentalmente as alterações gonadais presentes em indivíduos adultos de Astyanax altiparanae decorrentes da diminuição do nível da água. As coletas foram realizadas a cada quatro horas, iniciadas quatro horas antes e encerradas 28 horas após a estimulação, na Estação de Piscicultura da Companhia Energética de São Paulo, São Paulo, Brasil. As gônadas foram analisadas por microscopia de luz. As fêmeas apresentaram ovários na fase de apto à reprodução até 12h; em 16h, um estágio mais avançado desta fase; e, a partir das 20h, na fase de regressão. Os machos tiveram os testículos em fase de apto à reprodução até 8h; em 12h, um estágio mais avançado desta fase; e, a partir das 16h, o retorno à fase de apto à reprodução. A descrição morfológica foi corroborada pela proporção das classes celulares. As fêmeas apresentaram variação no índice gonadossomático, mas não foi estabelecido o esvaziamento das gônadas para nenhum dos sexos. O processo utilizado para a indução à reprodução foi considerado satisfatório, uma vez que ambos os sexos apresentaram redução no número de gametas maduros no final do período de amostragem.

Astyanax altiparanae is a Brazilian species of substantial commercial, environmental and scientific importance; however, existing studies on its reproduction do not seem to provide enough details. In light of the increasing use of this species in fish farming and the need for basic studies for the development of new production technologies, we describe the structural and ultrastructural characteristics of the ovaries of A. altiparanae, and characterize the species' reproductive cycle. Females were collected monthly from March 2013 to February 2014, and reproductive management began in October 2013. The ovaries were removed, fixed in Karnovsky's fixative, and prepared for light microscopy, transmission electron microscopy and immunohistochemistry anti-PCNA. These techniques enabled us to characterize the ovaries, the germ cells, and the somatic cells in detail, as well as their changes over time. The reproductive cycle was characterized based on the monthly variation in the gonadosomatic ratio, the proportion of germ cells, and the rate of oogonium proliferation. The macroscopic analysis of the ovaries suggests that the vascularization pattern and color of the ovaries vary according to development. There are new types of analyses that can be applied even in the fish farming industry, such as a comparison between ovaries staining and weight or the frequency distribution of these colors throughout the year. This study also provides details on microscopic characteristics that have never before been reported for species of Astyanax, such as the presence of annulate lamellae in oogonia, the development of the zona pellucida from oocytes in the one-nucleolus step, and the development of the micropylar apparatus in oocytes in the cortical alveolar step. When the reproductive cycle was analyzed, this species was found to have a long period of spawning, with a reproductive peak from October to February and multiple spawning events, confirming the period already described in the literature. Variations in reproductive periods and the ability to reproduce in lentic environments suggest that A. altiparanae has the ability to respond quickly to environmental changes and exhibits high reproductive flexibility. All of these characteristics confirm the great potential of this species in the fish farming industry.

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Studies on the morphology of the liver of teleosts reflect some controversy in the interpretation of the data, but also provide confirmation of variations in the structure of the organ in several species. Thus, we intend to understand the specific structural organization of the liver of Astyanax altiparanae. Specimens were collected in the city of Andirá, Paraná, Brazil. The livers were processed according to histological routine for inclusion in Paraplast, and the sections were stained with HE and Mallory's trichrome or followed the protocol for fluorescence immunohistochemistry, anti-cytokeratin. The liver of A. altiparanae was covered by a capsule of connective tissue, without delimiting lobes. The hepatocytes had an arrangement in cords around sinusoids. Melanomacrophage centers were observed. The vascular components and intrahepatic pancreatic acini were distributed between hepatocytes. Presence of cytokeratin was detected in tissues that lined the liver and endothelial cells of sinusoids. The comparison of the liver of A. altiparanae to other characids corroborates with the fact that there is variation in the morphology of the liver even between closely related species. Moreover, it appears that in this species, endothelial cells of sinusoids can synthesize the cytokeratin filaments required for the regulation of blood flow in capillaries in adults.

Gonadotropin‐releasing hormone (GnRH) is a key molecule in the initiation of the hypothalamic–pituitary–gonadal axis. Thus, knowledge about GnRH may contribute to the effectiveness of species reproduction. Using a Neotropical tetra Astyanax altiparanae as a fish model species, the GnRH forms were characterized at the molecular level and the role of injected GnRHs in vivo was evaluated. The full‐length complementary DNA (cDNA) sequences of preproGnRH2 (612 bp) and preproGnRH3 (407 bp) of A. altiparanae were obtained, and the GnRH1 form was not detected. The cDNA sequences of preproGnRH2 and preproGnRH3 were found to be conserved, but a change in the amino acid at position 8 of the GnRH3 decapeptide of A. altiparanae was observed. All the injected GnRHs stimulated lhβ messenger RNA (mRNA) expression but not fshβ mRNA expression, and only GnRH2 was able to increase maturation‐inducing steroid (MIS) levels and possibly stimulate oocyte release. Furthermore, only GnRH2 was able to start the entire reproductive hormonal cascade and induce spawning.

The objective of this study was to establish a protocol for the characterization, isolation, and culture of type A spermatogonia using specific molecular markers for these cells in fish. To this end, adult Prochilodus lineatus testes were collected and digested enzymatically and the resulting testicular suspension was separated using a discontinuous Percoll gradient, followed by differential plating. The cell cultures obtained were monitored for 15 days and analyzed using the immunofluorescence method with anti‐Vasa, anti‐GFRα1, and anti‐OCT4 antibodies. Spermatogonial enrichment was also performed using flow cytometry. Although discontinuous Percoll gradient centrifugation followed by differential plating enabled the removal of differentiated germ cells and somatic cells, enriching the pool of type A spermatogonia, the enrichment of type A spermatogonia through flow cytometry of samples without Percoll proved to be more efficient. Prominent cell agglomerates that were characterized according to different stem cell markers as type A spermatogonia were observed during the 15 days of the cell culture. The use of immunoperoxidase and western blot analysis methods confirmed the specificity of the markers for type A spermatogonia of P. lineatus. When combined with specific cell culture conditions, the positive characterization of these molecular markers clarified certain aspects of spermatogonial regulation, such as survival and proliferation. Finally, understanding the regulation of the in vitro germ cell maintenance process may contribute to the enhancement of in vivo and in vitro reproduction techniques of endangered or aquaculture fish species.

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