Transcriptomic analysis reveals the differential genes associated with skin growth and pigmentation between Red Melon and Red Cover Discus

This is the first report to describe the differential growth of cutaneous pigments and the molecular processes involved in two red discus ( Symphysodon spp.), Red Melon and Red Cover, with different tones of red pigmentation develop from juveniles to adults. Microscopic observation detected xanthophores in all samples, erythrophores in both adult groups and Red Melon juveniles, while melanophores were only found in Red Cover. The skin transcriptome analysis revealed extracellular matrix (ECM) activities and collagen metabolic genes were elevated in both juveniles, as compared to the adults. The development of erythrophores and xanthophores in the Red Melon juveniles were regulated by genes involved in the pteridine synthesis, one-carbon metabolism, and lipid metabolism. Temporal inhibition of melanophore development in Red Melon juveniles might be attributed to the active expression of Wnt-signalling inhibitor genes, sost and notum2 . Melanosome transport in Red Cover was likely relied on microtubules and the spectrin-associated cytoskeleton. Tyrosinase late N-glycan processing and its transport from Golgi apparatus into the melanosome were differentially expressed in RC adults and juveniles.