Keywords: 
• nonylphenol ethoxylates /
• Danio rerio /
• testicular histology /
• CYP450 enzymes

Abstract: In the present study, the effects of nonionic surfactant on testicular histology of adult male zebrafish (Danio rerio) were studied by the semi-static exposure test. The expressions of estrogen receptor α (ERα), androgen receptor (AR) and CYP450 enzymes related to sex steroid synthesis (CYP17, CYP19a) were measured using real-time polymerase chain reactions (qRT-PCR) method. Histological alterations of testicular structure of fish were also investigated after exposure. The results indicated that the NPEO exposure could cause histological alterations in the testicular structure and affect the mRNAs expressions of ERα, AR and CYP450 enzymes related to sex steroid synthesis in the adult male zebrafish. The exposure to the 10.0 mg·L^-1 NPEO could significantly up-regulate the expression of CYP19a, ERα and AR genes and down-regulate the expression of CYP17 gene in the testis of zebrafish. The number of both the spermatocysts and spermatozoans was found to be decreased, and some acellular zones appeared in the seminiferous tubule of fish exposed to the 0.1 mg·L^-1 NPEO. The congregated sperms in the lumen of seminiferous tubules and enlarged acellular zones were shown in the fish exposed to the 1.0 and 10.0 mg·L^-1 NPEO. Therefore, NPEO exposure could interfere the synthesis of testosterone by inhibiting the expression of CYP17 gene. Moreover, NPEO exposure could increase the synthesis of endogenous estrogen by inducing the expression of CYP19a and ERα genes and ultimately result in the alterations in the structure of zebrafish testis.