Factors affecting secondary sex characteristics in the yellowtail tetra, Astyanax altiparanae.

Diógenes H Siqueira-Silva,Rafaela M Bertolini,Nycolas Levy-Pereira,José A Senhorini,José Bento S Ferraz,George S Yasui,Lucas Henrique Piva,Nivaldo F Nascimento

doi:10.1007/s10695-020-00832-6

Abstract

This study interrogated factors which affect the appearance of secondary sexual characteristics, namely, fin spinelets (rigid dimorphic structure empirically associated with male sexual maturity in characids), in Astyanax altiparanae. Many variables such as the season of the year and several biotic components, including organism length, sex, phase of maturation, and the presence of gonads, were investigated. These factors were then associated with the physiological development of fin spinelets. The development of this trait is related to reproductive strategies but demonstrates considerable population variability as it is found throughout the year in some species but only during specific periods in others. Seventy-five specimens obtained from spontaneous spawn of farmed fish were arbitrarily grouped into small-, medium-, and large-sized groups in both summer and winter. Gonadal histology was performed to confirm each animal's sex and phase of maturation. Diaphanization of the fish was performed to visualize, count, and measure the fin spinelets. Finally, gonadectomization of some males was utilized to investigate the gonadal effect on the presence of fin spinelets. The present results show that the presence of fin spinelets is a secondary sexual characteristic of males which occurs independently of the season and is always present in males longer than 48 mm. However, in the summer, male specimens presented more rays with fin spinelets than during the winter. Furthermore, since fin spinelets were observed on immature males as well as spawning capable males, their presence cannot be directly associated with sexual maturity in male A. altiparanae, as previously supposed. Finally, gonadectomization resulted in an initial reduction in the length of fin spinelets. However, this trend was eventually normalized with time.

Highlights

Most teleost fish spawning is a seasonal event that depends on a series of environmental conditions that triggers reproductive migration and subsequent gonadal maturation
The yellowtail tetra A. altiparanae used in this study were collected from Mogi
The difference is structural, such as in guppy (Poecilia reticulata), in which a copulatory organ, named gonopodium, develops from the male anal fin to be used in internal fertilization (Tian et al, 2015)

Summary

Introduction

Most teleost fish spawning is a seasonal event that depends on a series of environmental conditions that triggers reproductive migration and subsequent gonadal maturation. Species such the yellowtail tetra Astyanax altiparanae presents intertidal spawning and may reproduce several times along the year (Orsi et al, 2004), including the winter season. The objective of sexual reproduction is to proceed gametogenesis, which leads to fertilization; changes in behavior or the hypertrophy of specific structures are concomitant to these processes. They may influence the success rate of fish reproduction, reflecting on both their physiology and behavior. Female red snapper Lutjanus campechanus are vastly more productive than smaller specimens (Bohnsack, 1998) and, in the black rockfish Sebastes melanops, older female produce larvae with a higher growth rate and more resistant to starving (Berkeley et al, 2004)

Objectives

Methods

Results

Discussion

Conclusion