Effects of temperature on gonadal differentiation of black rockfish(Sebastes schlegelii) and its mechanism

In this study, the black rockfish (Sebastes schlegelii) was selected as the research object. Three groups with different temperature treatments were set up, including high temperature group (24 °C), control group (20 °C) and low temperature group (16 °C). Histology, ELISA and qRT-PCR methods were used to investigate the effect of different temperatures on gonadal differentiation and the potential mechanism. The results showed that at 40 dpb, the gonads developed fastest at 24 °C, and slowest at 16 °C. The female ratio were 70.0%, 42.9% and 33.3%, at 24 °C, 20 °C and 16 °C respectively. At 24 °C and 20 °C, high level of E₂ lasted for a long time and T level decreased sharply at 30-35 dpb. At 16 °C, E₂ level dropped rapidly, and the T was still at a high level at 35 dpb. It indicated that at high temperature, the E₂ level was high, whereas T level was fairly low during gonad differentiation, and the gonad tended to be female; on the contrary, the gonad preferred to be male. At 24 °C, the cyp19a1a mRNA expression was significantly up-regulated at 35-40 dpb, which may be associated with the partial female gonad development at high temperature. At 16 °C, The ERβ2 mRNA expression was significantly decreased at 30-50 dpb. The inhibition of ERβ2 expression may be related to the partial male gonad development at low temperature. At 24 °C and 20 °C, foxl2 mRNA expression was at relative high level at 25-35 dpb, and the expression level of low temperature treatment group began to increase at 30 dpb. It indicated that the high expression of foxl2 may be related to the rate of ovarian differentiation during the early stage of gonadal differentiation. At 30-50 dpb, the general trend of expression levels of sox3, sox9 and dmrt1 was consistent, indicating there is a connection between the expressions of the three genes, which might be related to the rate of testis differentiation.