Research Group on the Reproduction of Amazon fish (GERPA/LANEC), Biology Faculty (FACBIO), University of South and Southern of Pará (Unifesspa), Marabá, Pará, Brazil; 2Laboratory of Fish Biotechnology, National Center for Research and Conservation of Continental Fish, Chico Mendes Institute of Biodiversity Conservation, Pirassununga, SP, Brazil; 3Reproductive and Molecular Biology Group, Department of Morphology, Institute of Biosciences, São Paulo State University (UNESP), Botucatu, Brazil; 4Department of Veterinary Medicine, FZEA, University of São Paulo, Pirassununga, SP, Brazil and 5PPG in Biodiversity and Biotechnology (BIONORTE).
Summary
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.
Introduction
Popularly known as ‘tambiú tetra’, Astyanax bimaculatus (Linnaeus 1758) is a fish species belonging to the Characidae family, which is mostly comprised of freshwater fish from Brazil. According to Fricke et al. (2018), this family contains approximately 1177 valid species of fish. Among these, A. bimaculatus is considered as one of the most important in the Astyanax genus (Vilela and Hayashi, 2001). Its ample distribution from the Brazilian northeast region to the Prata basin, large harvests and its importance in the sport of fishing are highlighted (Barbieri et al., 1982). In addition it is the main constituent of some fish diets that include ‘saicanga’ (Oligosarcus longirostris), and ‘traíra’ (Hoplias malabaricus) (Andrian et al., 2001).
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