Warm Water Induces Apoptosis, Gonadal Degeneration, and Germ Cell Loss in Subadult PejerreyOdontesthes bonariensis(Pisces, Atheriniformes)

Abstract

Recent studies have shown that exposure to warm water can trigger gonadal degeneration and germ cell loss in fish of both sexes, but the mechanism behind this pathology is still not understood. This study was designed to characterize this process histologically and determine whether apoptosis plays any role during high temperature-induced gonadal cell degeneration in subadult pejerrey (Odontesthes bonariensis). For this purpose, fish were reared continuously at constant temperatures of 24 degrees C (control) and 29 degrees C (prolonged heat stress) or exposed for 36 h to 31 degrees C and then returned to 24 degrees C (short heat stress). Gonads were sampled at various times (hours, days, weeks) after the start of the experiment and were analyzed by light microscopy and stereometry for histological integrity/degeneration and germ cell counts, as well as by acridine orange fluorescence microscopy, TUNEL, and caspase activity assay for histochemical and biochemical signs of apoptosis. The results clearly implicate apoptosis in heat-induced somatic and germ cell degeneration in pejerrey and revealed that the dynamics and severity of this process were proportional to the magnitude of the thermal stress. Even a 36-h exposure to 31 degrees C induced significant increases in caspase-3 activity and number of apoptotic cells in both sexes, but males were shown to be more sensitive to heat stress than females.

The Reversible Sex of Gonochoristic Fish: Insights and Consequences

“…However, this was not the case in the goldfish [Goto et al, 2012]. In the TSD pejerrey, germ cell apoptosis by high temperatures alone [Strüsmann et al, 1998] or coupled to busulfan did not affect the sex ratio of the sterile gonad [Ito et al, 2008;Yamamoto et al, 2013]. Likewise, our group [Almin et al, unpubl.…”

Analysis of Sexually Dimorphic Expression of Genes at Early Gonadogenesis of Pejerrey <i>Odontesthes bonariensis</i> Using a Heterologous Microarray

“…The present results are in agreement with previous work whereby apoptotic signals were found to be restricted to the anterior sections of the right gonads, which is most probably related to the antero-posterior and left-to-right gradient of histological sex differentiation in pejerrey Strüssmann et al, 2008]. However, it is important to note that long exposures to high temperatures can cause degeneration of somatic and germ cells in pejerrey larvae and juveniles, resulting in a clear decrease in the number of germ cells up to complete sterilization [Ito et al, 2008;Strüssmann et al, 2008].…”

High temperature-induced sterility in the female Nile tilapia, Oreochromis niloticus

“…The role of the epigenetic alterations in high-temperature-induced germ cell loss in the fish ovary requires further investigation. In many other species of fish, germ cells were found to be degenerated and undergoing apoptosis due to treatments with a high temperature and gonadal aromatase activity was also significantly reduced due to high temperature treatment (Ito et al, 2008;Uchida et al, 2004). In medaka, high temperature (32-34°C) inhibited germ cell proliferation and caused a female-to-male sex reversal, which was found to be mediated by increased levels of circulating cortisol (Hayashi et al, 2010).…”