A case of intersex occurrence in Steindachneridion parahybae (Steindachner, 1877) (Siluriformes: Pimelodidae) under captivity condition: a cytogenetic and morphological study

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.Poco se sabe sobre la biología reproductiva de Steindachneridion parahybae, una especie de teleósteo gonocorístico en peligro de extinción que habita la cuenca del río Paraíba do Sul y en éste trabajo se describe por primera vez la aparición de individuo intersexo en juvenil de S. parahybae. También se describió el aspecto normal de los ovarios y de los testículos de individuos juveniles procedentes del mismo lote de cría para su comparación; se realizó además el análisis citogenético. Un espécimen fue clasificado a priori como hembra debido a las características macroscópicas de los ovarios, con pequeños oocitos amarillos, sin flecos (característica principal de los bagres macho) y más grande que los testículos; sin embargo el análisis microscópico reveló la presencia de un ovotestis, incluyendo una espermatogénesis completa. S. parahybae presentó un número diploide, 2n = 56 cromosomas, sin evidencia de cromosomas sexuales diferenciados o supernumerarios entre ellos. Estos hallazgos pueden deberse al resultado de la exposición de los individuos a desorganizadores endocrinos o estar influenciados por las condiciones ambientales. Sin embargo no se puede descartar la posibilidad de la presencia de intersexos de forma espontánea. Por lo tanto, la importancia funcional y las consecuencias reproductivas de estas anomalías permanecen aún sin ser determinadas, sugiriendo que esta especie puede ser susceptible a los disruptores endocrinos. Estos resultados contribuyen a ampliar el conocimiento de la biología reproductiva de esta especie en peligro de extinción en condiciones de cautiverio.

Gonadotropins and Growth Hormone Family Characterization in an Endangered Siluriform Species, Steindachneridion parahybae (Pimelodidae): Relationship With Annual Reproductive Cycle and Induced Spawning in Captivity

“…As described to FSH, there is no protocol (i.e., specific antibodies) to measure plasma levels of LH in S. parahybae , therefore, the development of assays to measure these GtHs in siluriform species plasma can be useful. Furthermore, other preliminary studies in our laboratory are focused on the steroid synthesis pathways and oocyte development (Honji et al, ) throughout the reproductive cycle and after AIS in these females, together with the study of neurohormonal modulation at the brain by gonadotropin‐releasing hormone (GnRH) (Honji et al, ). In this regard, data about GnRH systems, steroid synthesis pathways and oocyte development must be interpreted together to assemble the puzzle that is reproductive dysfunction in S. parahybae females in captivity.…”

Mobilization of energetic substrates in the endangered catfish Steindachneridion parahybae (Siluriformes: Pimelodidae): changes in annual reproductive cycle in captivity

“…Then, they were randomly divided into two ponds (200 m 2 ) (duplicate) with concrete walls and a sandy bottom. During the experiment, the broodstocks were fed with commercial extruded feed for carnivorous fish containing 40% of crude protein at a rate of 2% biomass/day, offered twice a day (according to CESP fish farm routine), at 08:00 and 16:00h, following previously studies (Honji, 2011;Honji et al, 2012Honji et al, , 2013Honji et al, , 2016. During the experiment, the water temperature was 21.10 ± 0.14 ºC and the dissolved oxygen was 7.58 ± 0.36 mg/L, without significant variation between tanks.…”

“…It is a Neotropical catfish (gonochoristic, medium-sized), endemic to the Paraíba do Sul River Basin, critically endangered in the Brazilian red list, and considered regionally extinct in the state of São Paulo (Garavello, 2005;Caneppele et al, 2009;Honji et al, 2009Honji et al, , 2012Honji et al, , 2013Honji et al, , 2015Honji et al, , 2016Honji et al, , 2017. Besides this critical situation, the maintenance of S. parahybae female broodstock in fish farms is not entirely successful, as females do not reproduce when reared in captivity, i.e, females fail to ovulate or spawn naturally (Honji et al, 2015), despite their continuous feeding.…”

“…Since 2003, the energy company Companhia Energética de São Paulo (CESP) has funded studies on the biology of S. parahybae. These studies include the maintenance and management of broodstocks in captivity, egg and sperm quality, and successful larval rearing (Honji et al, 2009(Honji et al, , 2013(Honji et al, , 2015(Honji et al, , 2016(Honji et al, , 2017Sanches et al, 2013Sanches et al, , 2014Sanches et al, , 2015. They aim at ensuring successful and controlled breeding programs, involving conservation actions and a fish restocking program.…”

“…In the last few years, our research group and collaborators have advanced the knowledge on fundamental aspects of the reproductive biology of S. parahybae in captivity (Caneppele et al, 2009Honji et al, 2012Honji et al, , 2013Honji et al, , 2015Honji et al, , 2016Honji et al, , 2017Sanches et al, 2013Sanches et al, , 2014Sanches et al, , 2015Lopes et al, 2015). Knowledge of mobilization and deposition of energetic substrates on different tissues linked to their function in the reproductive cycle is required to understand the energetic requirement of S. parahybae, support further studies on broodstock nutrition, and contribute to the conservation of the species.…”