Dynamics and histological characteristics of gonadal sex differentiation in pejerrey (Odontesthes bonariensis) at feminizing and masculinizing temperatures

Abstract

This study evaluated the effects of different temperatures on the histological process of sex differentiation in the pejerrey Odontesthes bonariensis, a fish with marked temperature-dependent sex determination (TSD), at feminizing, neutral, and masculinizing temperatures. Fish reared at three temperatures (17 degrees C, 24 degrees C, and 29 degrees C) from hatching were sampled weekly until 11 weeks and their gonads were examined by histology. The percentages of females at 17 degrees C, 24 degrees C, and 29 degrees C were 100%, 73%, and 0%, respectively. Sex differentiation occurred earlier and at a smaller body size at higher temperatures in both sexes. The first signs of ovarian differentiation were observed at 4 and 7 weeks at 24 degrees C and 17 degrees C, respectively, and those of testicular differentiation at 4 and 7 weeks at 29 degrees C and 24 degrees C, respectively. Body or gonadal growth rates before sex differentiation were not proportional to temperature and showed no sexual dimorphism at 24 degrees C, where both sexes were present. Thus, differential growth rate is probably not a factor in TSD or histological sex differentiation in pejerrey. Blood vessels were formed before sex differentiation in both sexes and at all temperatures, and may be important for sex differentiation. No signs of intersexuality were found in any of the groups, and this characterizes pejerrey as the differentiated type of gonochorist even at feminizing and masculinizing temperatures. Ovaries were formed by the same histological processes at feminizing (17 degrees C) and neutral (24 degrees C) temperatures and without any pathological features such as germ cell degeneration. The process of testicular formation was generally similar at 24 degrees C and 29 degrees C, but some fish at 29 degrees C had widespread germ cell degeneration before sex differentiation. This suggests that pathological processes leading to germ cell death, such as heat-induced dysfunction of the supporting somatic cells, could be involved in masculinization of the genetic females at high temperatures.

Expression profile and estrogenic regulation of anti‐Müllerian hormone during gonadal development in pejerrey Odontesthes bonariensis, a teleost fish with strong temperature‐dependent sex determination

“…For the thermal manipulation experiment, approximately 400 newlyhatched larvae were stocked in three 60-L tanks set at 17 Ϯ 0.5°C (FPT), 25 Ϯ 0.5°C (MixPT), and 29 Ϯ 0.5°C (MPT). The choice of temperatures followed Str¨ussmann et al (1997) and Ito et al (2005). The larvae were reared in flowing brackish water, under a 16L-8D light cycle, and were fed daily to satiation with Artemia nauplii and powdered fish food (TetraMin flakes, Melle, Germany).…”

“…Specimens were then dehydrated, embedded in Paraplast Plus, cut in 6-m- thick serial sections, and stained with hematoxylin-eosin. Histological preparations were examined under a microscope to identify females and males using as criteria the presence of the ovarian cavity or the efferent duct, respectively, as previously established by Ito et al (2005). The time of histological sex differentiation for each treatment was defined as the week when Ն50% of the samples had clear ovaries or testes according to the above criteria.…”

The effect of rearing temperature in larval development of pejerrey, Odontesthes bonariensis: morphological indicators of development

“…In the pejerrey Odontesthes bonariensis, water temperature not only affects growth rates but also directs the sexual differentiation process (Strüssmann & Patiño, 1995;Ito et al, 2005). This species presents a strong temperature sex determination (TSD), a form of environmental sex determination (ESD) where 100% female or male populations can be obtained simply by controlling water temperature (Strüssmann et al, 1996a).…”

Cambios Morfológicos en la Ontogenia Temprana de Chirostoma riojai

“…Es por esto, que los cambios morfológicos que sufren durante su ontogenia están estrechamente relacionados con su hábitat (Macpherson, 1998). Una de las condiciones ambientales que afecta o determina los tiempos de desarrollo y aspectos fisiológicos es la temperatura (Angilleta et al, 2004), ya que esta puede modificar las tasas de crecimiento e influye en la determinación del sexo de estos organismos (Ito et al, 2005; Strussmann et al, 2010).…”

“…Es por esto, que los cambios morfológicos que sufren durante su ontogenia están estrechamente relacionados con su hábitat (Macpherson, 1998). Una de las condiciones ambientales que afecta o determina los tiempos de desarrollo y aspectos fisiológicos es la temperatura (Angilleta et al, 2004), ya que esta puede modificar las tasas de crecimiento e influye en la determinación del sexo de estos organismos (Ito et al, 2005; Strussmann et al, 2010).Los trabajos de descripción morfológica posterior a la fase de embrión libre para el género Chirostoma son pocos y se basan principalmente en determinar la supervivencia y tasa de crecimiento de los ejemplares, describiendo únicamente la morfología basada en la aparición de las aletas y otras estructuras como la placa hipúrica. En los estudios que se describen el crecimiento y el desarrollo temprano de los peces se utiliza la morfometría tradicional como herramienta para su análisis.…”