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Oogenesis in fish is a process that involves cell proliferation, growth and maturation. In rivers blocked by hydroelectric dams, these factors can be altered and affect the reproduction mechanism of the species. Regarding this scenario, the present study aimed to describe oogenesis in two cichlids native to the Amazon basin, Geophagus argyrostictus and G. altifrons, during pre- and post-dam periods of the Xingu River. Females of both Geophagus species were captured and biometric measurements were taken. Afterwards, the fish were euthanized, and the gonads were removed and subjected to histological processing for light microscopy, scanning electron microscopy and immunoperoxidase staining. Oocyte diameter and zona radiata thickness were also measured. The ovaries appeared in pairs, where according to their shape, size, vascularization and cell organization, five stages were described for both species. In the post-dam period, there was a reduction in the mean diameter of the oocytes, especially type IV, and a decrease in the thickness of the zona radiata, mainly, in G. argyrostictus. In both species, there was a greater presence of oocyte atresia in the post-dam period. PCNA immunoreactivity was more intense in type I and II oocytes, while vitellogenin immunoreactivity occurred in the cytoplasm and follicular cells of oocytes III and IV. These data suggest that because of changes in the level/flow of the river, the gonads of these two species adjust to the new environment, with a decrease in mean diameter and zona radiata thickness of the oocytes, which can interfere with the reproduction of the animals., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest for the publication of this study., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Studies related to morpho-physiology improve the understanding of biological mechanisms in non-human primates (NHP), contributing to research in several areas, especially those of assisted reproduction and biomedicine. The genera Aotus and Sapajus are important considerations in conducting studies related to reproductive biology and biomedical research, where animals of these genera can serve as models for species with vulnerable conservation status. The reproductive functions of animals of these genera can be used in conducting studies with other NHP species, for which biological material is difficult to access. The aim in conducting the current review was to compile the scientific literature on the biology and reproductive aspects of these two genera, to provide a for a greater understanding of these topics. In addition, a systematic review of literature allows for efficient access relevant information from an extended timeframe collated in a single document. There was, therefore, a systematic search for keywords based on reproductive studies with animals in these genera conducted, and 58 articles, 12 books, and three academic theses were subsequently selected. Even though there have been advances in knowledge of the reproductive biology of animals from these genera that have occurred in recent decades, especially research conducted when these NHP were in captivity, a wide variety of areas remain to be studied so that the understanding of reproduction in these NHP can be enhanced and the knowledge gained from these studies utilized for greater understanding of reproduction of NHP in general., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The present study was conducted to assess the testicular structure and germ cell ultrastructure of Hypophthalmus marginatus during spermatogenesis. Semen and sections of the mid-region of the testis were collected, processed, and analyzed using optical and electron microscopy. Macroscopically, the testes of H. marginatus were filiform, and the testicular parenchyma was composed of spermatogenic cells that proliferated, organized within spermatic cysts. During spermiogenesis, spermatids had no nuclear rotation. The proximal centriole was perpendicular to the distal centriole, characteristic of type III spermiogenesis. Spermatozoa were released into the lumen of the seminiferous tubules and had an ovoid head without an acrosome, condensed nucleus, and shallow nuclear fossa. The midpiece was short, with a single long flagellum. The flagellum had the typical axoneme structure, with nine pairs of peripheral and a central pair of microtubules. The thin end piece comprised only peripheral microtubules. Spermatogenesis in H. marginatus features filiform testes, cystic spermatogenesis, and type III spermiogenesis., (Copyright © 2019 Elsevier B.V. All rights reserved.)