The hybrid species red tilapia (Oreochromis spp.) is favored in aquaculture for its bright color, rapid growth, and high market value. However, color variation hinders market development, which is influenced by both genetic and environmental factors. We aim to identify candidate genes and pathways related to pigmentation, uncovering the molecular basis of these color variations in red tilapia by employing third-generation full-length transcriptome sequencing combined with second-generation transcriptome analysis. Our analysis focused on three distinct phenotypic classes: whole pink, pink with black blotch, and whole black. Pigment cell and pigment composition analysis highlighted that the pigment pattern in red tilapia is primarily determined by the distribution and interaction of various pigment cells, including melanophores, xanthophores, erythrophores, and iridophores. The whole pink individuals were characterized by an absence of melanophores and a high concentration of carotenoids, while the whole black individuals exhibited active melanogenesis. Transcriptomic data indicated that genes associated with melanin synthesis (wnt, fzd7, lef, tcf7, tyrp1, oca2, pmel, bmp2, cbs) were up-regulated in whole black individuals, while genes related to carotenoid uptake and deposition (scarb1, ldlr, ttc39b, stard5, stard10, plin2, fitm2, bscl2), as well as pteridine synthesis (gch1, ptps), were more actively expressed in whole pink individuals. Retinol metabolism was identified as a mediator of the interaction between melanin synthesis and carotenoid deposition. Further, alternative splicing (AS) act as a crucial post-transcriptional mechanism regulating body coloration, beyond transcriptional differences. Analysis of AS events identifies multiple splice variants of pigment-related genes (scarb1, pax7, ctnnb1, rxrb, bscl2, gjb10, bmp4, frzb) that exhibit differential expression and splicing patterns across different color phenotypes. Notably, AS events of the scarb1 gene, related to carotenoid deposition, and the polr2d gene, associated with the transcription machinery, may significantly influence pigment deposition patterns in red tilapia. Our work not only deepens the genetic understanding of pigmentation in red tilapia but also establishes a solid foundation for improving color stability through selective breeding and genetic improvement programs across various hybrid species in aquaculture, which is crucial for marketability and consumer attraction.
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