Transcriptome analysis of discus fish (Symphysodon haraldi) skin and brain to identify genes involved in ‘milk’ secretion during parental care

The discus fish Symphysodon spp., an Amazonian cichlid, employs an unusual parental care behavior where free-swimming fry feed on parental epidermal mucus after hatching. However, little is known about the mechanism by which discus secrete ‘milk’ and the genes involved. In order to study the unique behavior of discus fry feeding on parental skin mucus on the molecular level, transcriptome sequencing was performed on the skin and brain of female discus. Through the analysis of skin transcriptome sequencing data, 228 differentially expressed genes were obtained by comparing parental with non-parental fish, including 126 up-regulated genes and 102 down-regulated genes. For the brain, 86 differentially expressed genes were obtained including 71 up-regulated genes and 15 down-regulated genes. Through the analysis of pathway in the skin, 7 metabolic pathways were obtained: arachidonic acid metabolism pathway, adhesion pathway, apoptosis, steroid biosynthesis, tuberculosis, P53 signaling pathway, serotonergic synapse, which were related to 10 differentially expressed genes: JUNB, MRC, DPP3, CASP3, PPID, ITGA11, ALOXE3, HBE, PTPRJ, GALE. Meanwhile, the analysis of pathway in the brain, 20 metabolic pathways were obtained e.g., estrogen signaling pathways, inflammatory medlator regulation of TRP channels, non-small cell lung cancer, vascular smooth muscle contraction, which were related to 9 differentially expressed genes: PRKCD, H1-5, EDNRB, LAPTM, FOXB, OTX2, NRIF2, SOX1 and HBE.