Secondary sex characteristic in Brycon orbignyanus (Characiformes: Bryconidae) and its association with testicular development

Abstract

Secondary sex characters are differences between males and females that are not related to reproductive organs, but are directly related to morphological differences present throughout life, like size and coloration or by accessory structures associated with the reproduction period, indicating a degree of sexual dimorphism. At Brycon orbignyanus the sexual maturation is relatively late and males can be differentiated in the reproductive period by a roughness found in the anal fins called spicules. However, although present in the reproductive period, there isn't much information about the synergy between the appearance of spicules and testicular development. Thus, this work has for objective to analyze the secondary characteristics of B. orbignyanus males, relating them to the stages of the reproductive cycle of these animals, based on the use of spicules for the development for a possible protocol for selection of breeding males in induced reproductions. Therefore, B. orbignyanus specimens from an accompanying reproduction will be used from the squad of the U.H.E. de Promissão - AES - Tietê, Promissão / SP and transferred to Neotropical Ichthyology Laboratory - LINEO, UNESP / FEIS. Males of B. orbignyanus will be collected monthly from August 2020 to February 2021 and selected according to the presence or absence of spikes in the anal fin (n = 10 per month analyzed). For the histological reviews the testicles will be fixed in Karnovsky solution (2% glutaraldehyde, 4% paraformaldehyde, and Sorensen phosphate buffer solution), and will be included and impregnated in Leica® methacrylate glycol resin and then cut into a semi-automatic Leica® RM-2245 microtome in 3µm sections, which will be stained with Hematoxylin / Eosin (H.E.). For analysis of the anal fins of B. orbignyanus males, the material will be collected and fixed in Karnovsky solution, prepared for scanning electron microscopy (SEM) and for diaphanization processes (cartilages stained by immersion in Alcian Blue solution and bones stained with Alizarin dye for 24 hours and further preservation in glycerin). (AU)