Abstract
ABSTRACT Little is known about reproductive biology of endangered Steindachneridion parahybae , a gonochoristic teleost species inhabiting the Paraíba do Sul River Basin, and herein is the first description of intersex in S. parahybae juvenile. The normal appearance of ovaries and testes in juvenile from the same lot of breeding were also described for comparison, even as cytogenetic analysis was performed in these juveniles. One specimen was a priori classified as female due to the macroscopic characteristic of ovaries, with small yellow oocytes, without fringes (a main characteristic of catfish male), and larger than testes; however the microscopic analysis revealed the presence of ovotestes, including the complete spermatogenesis. S. parahybae had diploid number, 2n = 56 chromosomes with no evidence of differentiated sex chromosomes or supernumerary chromosomes among them. These findings may be due to the result of exposure to endocrine disrupting compounds or may also be influenced by environmental conditions. The possibility of intersexes might also happen spontaneously and it cannot be ruled out. Therefore, the functional significance and reproductive consequences of this anomaly remain to be determined, suggesting that this species may be susceptible to endocrine disruption. These results contribute to gain expertise about reproductive biology of an endangered species in captivity.
Highlights
As shown by Nelson (2006) fishes are the speciesrichest group among vertebrates, comprising slightly more than one-half of the number of vertebrate species (54,711) known to date
It’s important make sure that, this study is associated with the project “Environmental influences on the mechanisms of sex determination and differentiation in teleost fish”, undertaken by Honji (2011b) whose main aim is to analyze the possibility that thermmolabile sex determination and/ or sex differentiation in teleost fish
As showed by Ferraris (2007), the teleost order Siluriformes (Ostariophysi) that includes the largest number of living teleost fish species, contains 3.093 species popularly known as “catfish”
Summary
As shown by Nelson (2006) fishes are the speciesrichest group among vertebrates, comprising slightly more than one-half of the number of vertebrate species (54,711) known to date. They present a notable level of diversity at all the biological levels of organization, which affect their morphology, physiology, behavior, ecology and genomes, as well as multiple other aspects of their biology (Volff, 2005). Teleost fish species represents a heterogeneous group and presenting eight systems of sex determination controlled by sex chromosomes (Devlin & Nagahama, 2002). Cytogenetics studies are used as important tools for the understanding of different aspects such as sex determination mechanisms or sex differentiation process, sex chromosomes evolution, existence of supernumerary chromosomes, among other researches (Pisano et al, 2007)
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