High temperature causes masculinization of genetically female olive flounder (Paralichthys olivaceus) accompanied by primordial germ cell proliferation detention

Experimental results revealed that high temperatures caused juvenile olive flounder masculinization (male ratio, 95.24%, 27.5 °C ± 0.5 °C) in comparison with controls (male ratio 5.56%, 18 °C ± 0.5 °C). The proliferation pattern of germ cells presented sexual dimorphism, from 42 to 66 days post-hatching (dph). The experimental group presented specifically slow proliferation and greatly reduced cell numbers. No cyst clusters were apparent in comparison to the control group. Consistently, the proliferation activity of germ cells in the experimental group was significantly reduced in comparison to that observed in the control group at 50 dph by PCNA immunohistochemistry. Furthermore, the expression levels of poamh during the process of temperature-induced masculinization gradually increased and were significantly higher than that in the control group at the stage gonads have been considered still undifferentiated in particular from a histological point of view. Thus, elevated temperatures result in masculinization, poamh up-regulation, accompanied by germ cell detention proliferation.