ABSTRACT
The discus fish (Symphysodon aequifasciatus) is an ornamental fish that is well-known around the world. Phenotype investigation indicated that there are no significant differences in appearance between males and females of the discus fish. To better understand the sexual development mechanisms and obtain a high efficiency sex identification method in the artificial reproduction process of the discus fish, we constructed six cDNA libraries from three adult testes and three adult ovaries, and perform RNA-sequencing for identifying sex-biased candidate genes, microRNA (miRNA), and metabolic pathway using the Illumina Hiseq 4000. A total of 50,082 non-redundant genes (unigenes) were identified, of which 18,570 unigenes were significantly overexpressed in testes, and 11,182 unigenes were significantly overexpressed in ovaries, and 8 differentially expressed unigenes were validated by quantitative Real-Time PCR (qPCR). A total of 551 miRNAs were identified, of which 47 miRNAs were differentially expressed between testes and ovaries, and 7 differentially expressed miRNAs and one non-differential miRNA were validated by qPCR. Twenty-four of these differentially expressed miRNAs and their 15 predicted target genes constituted 41 important miRNA-mRNA interaction pairs, which may be important candidates for sex-related miRNAs and sex-related genes in the discus fish. Some of vital sex-related metabolic pathways were also identified that may play key roles in regulating gonad development of the discus fish. These results can provide important insights to better understand molecular mechanisms for sexual dimorphism in gonads development.
