Transcriptome Profiling Reveals Stage-Specific Regulation of Lipid Metabolism in Orbital Fat of Bighead Carp (Hypophthalmichthys nobilis)

The orbital fat of bighead carp (<i>Hypophthalmichthys nobilis</i>) represents a structural fat deposit located posterior to the eyes and constitutes an important edible component of the head region. Nevertheless, molecular mechanisms governing lipid accumulation during ontogenetic development remain insufficiently characterized. Here, we performed RNA-Seq on orbital fat tissues from 6-month-old (juvenile) and 18-month-old (market-size) bighead carp. A total of 1042 DEGs were identified, with 807 up-regulated and 235 down-regulated in the 6-month-old stage. Functional enrichment revealed key pathways including fatty acid metabolism, PPAR signaling, and glycolysis/gluconeogenesis. qRT-PCR validation confirmed RNA-Seq reliability. Notably, the differential expression patterns of genes such as <i>cpt1a</i>, <i>cpt1b</i>, <i>slc27a1</i>, <i>fads2</i>, and <i>scd</i> suggest their association with an elevated capacity for lipid synthesis in the orbital fat of 18-month-old bighead carp. This study presents the first transcriptome analysis of orbital fat development in a freshwater fish, offering insights into the genetic improvement of head meat quality traits and growth in bighead carp head.