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Due to sexual dimorphism in growth traits, all-female populations and populations with a high proportion of females hold significant economic value in common carp (Cyprinus carpio L.). However, the underlying mechanisms governing gonadal differentiation remain inadequately understood. NF-κB, as a crucial regulator of anti-apoptotic processes, plays a significant role in mammalian gonad formation and zebrafish oocyte maintenance. To investigate the potential roles of the NF-κB pathway in the gonad differentiation of common carp, juveniles with undifferentiated gonads were treated with an activator (DOC) or inhibitor (NAI) of NF-κB. Our findings revealed that juveniles exposed to DOC exhibited a significantly increased female-to-male ratio (from 0.97:1 to 4.30:1) and substantial increases in weight and body length. Conversely, inhibiting NF-κB with NAI resulted in a decreased female-to-male ratio (from 1.06:1 to 0.33:1). Furthermore, NAI also induced the occurrence of ovotestis. Additional in vivo and ex vivo experiments demonstrated that DOC activation of the NF-κB pathways led to inhibition of apoptosis, significant increases in serum 17β-estradiol (E2) levels and the E2/T ratio, and upregulation of the female-biased genes foxl2 and cyp19a1a. Simultaneously, it significantly suppressed serum 11-ketotestosterone (11-KT) levels and the expression of male-biased genes amh , dmrt1 , and gsdf and induced VTG levels in the hepatopancreas of male carp. However, NAI exhibited contrasting effects. Both DOC and NAI disrupted the balance of the hypothalamus-pituitary-gonad (HPG) reproductive axis at multiple potential loci, including changes in the expression levels of steroid hormone synthesis-related genes in gonads. Transcriptomic analysis revealed comprehensive molecular changes in undifferentiated gonads during DOC-induced feminization and NAI-induced masculinization. The transcriptome results were consistent with the observed alterations in hormone content and the expression of genes involved in sex hormone synthesis, inflammation, and apoptosis following exposure to DOC or NAI. These findings suggest the involvement of NF-κB in the sex differentiation of common carp by regulating apoptosis and disrupting the HPG reproductive axis. Our study also explores a DOC-induced method of producing high ratios of females and discovers the underlying mechanism of NF-κB's contribution to sex differentiation in common carp. • DOC induces high ratios of females and promotes the growth of common carp. • NAI results in a male-biased sex ratio and the appearance of ovotestes. • Apoptosis is involved in the process of feminization caused by activation of NF-κB. • The imbalance of the HPG axis contributes to the skewed sex ratio. [ABSTRACT FROM AUTHOR]

• The gonadal development was remarkably hampered by PVC microplastics. • PVC microplastics damaged histological structure of gonads and brains. • Disruption effects of PVC microplastics were observed in sex hormone levels. • Genes transcription and translation in HPG axis were changed by PVC microplastics The negative consequences of microplastics pollution on the health of aquatic species have garnered extensive attention. However, the mechanisms through which microplastics may cause harm in the reproductive processes of fish remain unknown. For this study, Cyprinus carpio var. was subjected to four treatments with various concentrations of PVC microplastics for 60 days, through food rationed diets (no plastic control, 10%, 20% and 30%). The gonadosomatic indices, gonad and brain histologies, sex hormone levels, and transcriptional and translational genes in the hypothalamic-pituitary-gonadal (HPG) axes of both sexes were observed. According to the results, the gonadosomatic indices were significantly decreased, gonadal development was delayed, and the level of estradiol (E2) in the females was significantly elevated. In addition, the expression levels of genes associated with the HPG axis in the brains and gonads (gnrh, gtha1, fshβ, cyp19b, erα, vtg1, dmrt1, sox9b, and cyp19a) and the transcription levels of apoptosis-related genes in the brains and gonads (caspase3, bax , and bcl-2) exhibited significant changes. Further investigation revealed that the translation levels of genes linked to sex differentiation and sex steroid hormone (cyp19b and dmrt1) were significantly altered. These findings indicated that PVC likely microplastics may have a negative impact on the reproductive system of Cyprinus carpio var. by inhibiting gonadal development, affecting the gonad and brain structures, and altering the levels of steroid hormones and the expression of HPG axis-related genes. This work provides new insights into the toxicity of microplastics in aquatic organisms by revealing that PVC microplastics are a potential threat against the reproduction of fish populations. [ABSTRACT FROM AUTHOR]