A First Insight into the Gonad Transcriptome of Hong Kong Catfish (Clarias fuscus)

SIMPLE SUMMARY: The male Hong Kong catfish (Clarias fuscus) grows significantly faster than females, and monocultured males are more commercially available. However, little is known about the molecular regulatory mechanisms of the gonadal development and reproduction process in Hong Kong catfish, limiting the development of monosex cultures. In this study, a high quality transcriptome was constructed from the testes and ovaries of Hong Kong catfish. The regulatory networks of sex-related pathways were explored through Gene Ontology (GO), Kyoto Encyclopedia of Gene and Genome (KEGG) pathway enrichment, and bioinformatics analyses. The results showed that sex-related pathways related to primordial germ cell development, oocyte maturation, gonadal development and steroid biosynthesis were significantly enriched in the gonad transcriptome. This is the first study on the gonad transcriptome of Hong Kong catfish, which provides an important molecular basis for the sex identification and sex-controlled breeding of these catfish. ABSTRACT: Hong Kong catfish (Clarias fuscus) exhibit sexual dimorphism, particularly in body size. Due to the fast growth rate of males, the sexual size dimorphism of Hong Kong catfish has become an economically important trait. However, limited knowledge is known about the molecular mechanisms of sex determination and sex differentiation in this species. In this study, a first de novo transcriptome sequencing analysis of testes and ovaries was performed to identify sex-biased genes in Hong Kong catfish. The results showed that a total of 290,291 circular consensus sequences (CCSs) were obtained, from which 248,408 full-length non-chimeric (FLNC) reads were generated. After non-redundant analysis, a total of 37,305 unigenes were predicted, in which 34,342 unigenes were annotated with multiple public databases. Comparative transcriptomic analysis identified 5750 testis-biased differentially expressed genes (DEGs) and 6991 ovary-biased DEGs. The enrichment analysis showed that DEGs were classified into 783 Gene Ontology (GO) terms and 16 Kyoto Encyclopedia of Gene and Genome (KEGG) pathways. Many DEGs were involved with sex-related GO terms and KEGG pathways, such as oocyte maturation, androgen secretion, gonadal development and steroid biosynthesis pathways. In addition, the expression levels of 23 unigenes were confirmed to validate the transcriptomic data by quantitative real-time polymerase chain reaction (qRT-PCR). This is the first investigation into the transcriptome of Hong Kong catfish testes and ovaries. This study provides an important molecular basis for the sex determination and sex control breeding of Hong Kong catfish.