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Piracanjuba (Brycon orbignyanus) is an endangered fish species from the Neotropical region. The establishment of a cryobank using spermatogonial stem cells (SSCs) and subsequent production of a germline chimera is thus a promising strategy for such species. In the present work, procedures for the isolation and cryopreservation of piracanjuba SSCs and subsequent transplantation into sterile recipients were established. The piracanjuba SSCs were obtained by Percoll density gradient centrifugation and differential plating. SSC fractions were evaluated by relative ddx4 expression, alkaline phosphatase activity, and light microscopy. SSC cryopreservation was performed using five cryoprotectants at three different concentrations. The mix of the cells from the 20% and 30% Percoll density gradients showed 58.35 ± 0.03% purity of SSCs. The purity of SSCs increased to 66.00 ± 0.01% after differential plating. The relative ddx4 expression was 3.5 times higher in cells from the Percoll density gradient centrifugation than in the gonad and cells after differential plating. Propanediol (1 M) was the most effective cryoprotector evaluated (P = 1.000), showing 90.75 ± 1.85% cell viability. Freshly isolated and cryopreserved cells from the Percoll density gradient centrifugation were transplanted into a sterile male adult triploid hybrid with germ cell-less gonads. SSCs were observed in the germinal epithelium of the testes of recipients 20 days after transplantation. The results are promising for obtaining functional germline chimeras in Neotropical fish. Consequently, although the number of males used for the experiment was borderline, the procedures established here can be applied in future actions for the conservation and reconstitution of the piracanjuba in case of extinction., Competing Interests: Declarations Ethics approval The experiments were conducted following the Animal Ethics Committee from the National Center for Research and Conservation of Continental Aquatic Biodiversity (CEUA/CEPTA #02031.000088/2021–61). The authenticity of the document can be verified on the website https://sei.icmbio.gov.br/autenticidade informing the verification code: 9643544 and the code CRC: EC53598A. Competing interests The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The use of model organisms is important for basic and applied sciences. Several laboratory species of fishes are used to develop advanced technologies, such as the zebrafish ( Danio rerio ), the medaka ( Oryzias latipes ), and loach species ( Misgurnus spp . ). However, the application of these exotic species in the Neotropical region is limited due to differences in environmental conditions and phylogenetic distances. This situation emphasizes the establishment of a model organism specifically for the Neotropical region with the development of techniques that may be applicable to other Neotropical fish species. In this work, the previous research efforts are described in order to establish the yellowtail tetra Astyanax altiparanae as a model laboratory species for both laboratory and aquaculture purposes. Over the last decade, starting with artificial fertilization, the yellowtail tetra has become a laboratory organism for advanced biotechnology, such as germ cell transplantation, chromosome set manipulation, and other technologies, with applications in aquaculture and conservation of genetic resources. Nowadays, the yellowtail tetra is considered the most advanced fish with respect to fish biotechnology within the Neotropical region. The techniques developed for this species are being used in other related species, especially within the characins class., Competing Interests: GY and JS were employed by Peixetec Biotecnologia Em Organismos Aquáticos LTDA. NV was employed by China Three Gorges Corp. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Yasui, Ferreira do Nascimento, Pereira-Santos, Santos Silva, Coelho, Visintin, Porto-Foresti, Okada Nakaghi, Vianna, Carvalho, Monzani, López and Senhorini.)

Molybdenum (Mo) and its isotopes have been used to retrieve palaeoenvironmental information on the ocean-atmosphere system through geological time. Their application has so far been restricted to rocks least affected by severe metamorphism and deformation, which may erase or alter palaeoenvironmental signals. Environmental Mo-isotope signatures can be retrieved if the more manganese (Mn)-enriched rocks are isotopically depleted and the maximum range of δ 98 Mo values is close to the ~2.7‰ Mo-isotope fractionation known from Mo sorption onto Mn oxides at low temperature. Here, we show that the Morro da Mina Mn-ore deposit in Minas Gerais, Brazil, contains Mn-silicate-carbonate ore and associated graphitic schist that likely preserve δ 98 Mo of Palaeoproterozoic seawater, despite a metamorphic overprint of at least 600 °C. The extent of Mo-isotope fractionation between the Mn-silicate-carbonate ore and the graphitic schist is similar to modern Mn-oxide precipitates and seawater. Differences in δ 98 Mo signals are broadly reflected in cerium (Ce) anomalies, which suggest an oxic-anoxic-stratified Palaeoproterozoic ocean.