Cytochrome P450 aromatase (P450arom) plays a pivotal role in ovary development. In this study, we used semi-quantitative reverse transcription PCR (RT-PCR) to analyze spatiotemporal expressions of two P450arom genes (CYP19A and CYP19B) and their responses to temperature stress in female yellow catfish (Pelteobagrus fulvidraco). Tissue distribution pattern of CYP19 showed that CYP19B was abundantly expressed in fish brain and ovary (brain > ovary), but weakly in intestines, whereas CYP19A was exclusively expressed in ovary. Semi-quantitative RT-PCR analyses showed high transcript abundance of both CYP19A and CYP19B in the ovarian reproductive cycle, corresponding with serum estradiol-17β (E 2 ) levels. Increases in aromatases, serum E 2 and testosterone (T) levels in fish exposed to higher temperature indicated stimulation of ovarian maturation and recrudescence by heat stress in stages Ⅱ and Ⅴ during the ovarian cycle, whereas associated decreases in stage Ⅲ suggested vitellogenesis inhibition by heat stress. Gene expression of CYP19 was closely related to levels of serum E 2 . Results demonstrated CYP19 played a crucial role in the reproductive cycle of female yellow catfish. Different temperature stress affected CYP19 gene expression in the fish ovarian reproductive cycle. Associated P450arom genes could be useful for studying physiological aspects of yellow catfish.

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Gonadotropin-releasing hormone receptor (GnRHR) gene is expressed at the anterior pituitary gland and plays a key role in gonad development. This study aimed to investigate molecular genetic characteristics of the GnRHR gene and elucidate the effects of single nucleotide polymorphisms (SNPs) of GnRHR gene on sex steroid level in Japanese flounder (Paralichthys olivaceus). We used polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) and sequencing of the GnRHR gene in 75 individuals. We identified three SNPs in the GnRHR gene: P1 locus (C759A and C830T) in the coding region of exon2 which were both linked together and P2 locus (G984T) in the coding region of exon3, which added a new transcript factor (ADR1) and a new methylation site (CG). Only C830T of P1 leads to amino acid changes Thr266Ile. Statistical analysis showed that P1 was significantly associated with 17β-estradiol (E 2 ) level (p<0.01) and gonadosomatic index (GSI) (p<0.05). Individuals with genotype BB of P1 had significantly higher serum E 2 levels (p<0.01) and GSI (p<0.05) than those of genotype AA or AB. Another SNP, P2, synonymous mutation, was significantly associated with GSI (p<0.05). Individuals with genotype AB of P2 had significantly higher GSI (p<0.05) than that of genotype AA. In addition, there was a significant association between one diplotype based on three SNPs and reproductive traits. The genetic effects for both serum E 2 level and GSI of diplotype D4 were super diplotypes (p<0.05). These results suggest that the SNPs in Japanese Flounder GnRHR are associated with E 2 level and GSI.

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As a specific gene of fish, cytochrome P450c17-Ⅱ (CYP17-Ⅱ) gene plays a key role in the growth, development and reproduction level of fish. In this study, the single-stranded conformational polymorphism (SSCP) technique was used to characterize polymorphisms within the coding region of CYP17-Ⅱ gene in a population of 75 male Japanese flounder (Paralichthys olivaceus).