Tissue Structure and Full-Length Transcriptome Analysis of the Scaly Sublayer of Cyprinus carpio var. Quanzhounensis

Cyprinus carpio var. Quanzhounensis, native to Quanzhou County, Guilin City, Guangxi, has a dark brown body color, translucent gill cover, and abdominal skin, and is an important farmed species in the local integrated rice-fishery industry. A comparative study on the skin of Cyprinus carpio var. Quanzhounensis revealed a lack of reflective guanine crystals on the body surface and a significantly higher melanin content than that of C. carpio var. Jian, which was tentatively considered the direct cause of variations in body color of this group. Iridocytes are a pigment cell species that contain regularly arranged guanine crystals, which are the key material basis for the metallic luster of the fish body surface. In species such as medaka (Oryzias latipes) and zebrafish (Danio rerio), the absence of guanine crystals is considered a manifestation of the absence of iridocyte differentiation and therefore is ideal for studying the mechanism of pigment cell differentiation. The pnp4a, Gbx2, sox10, tfec genes and other iridocyte-related genes have been mined using mutant materials, and we have uncovered the differentiation mechanism that regulates the formation of iridescent cells. C. carpio var. color has abundant genetic variation in body color and is a good material for studying the mechanism of body color determination in fish. The roles of ASIP and MC1R in the aggregation and distribution of melanin and formation of black spots in C. carpio var. color were verified. The guanine crystalline deletion trait of C. carpio var. Quanzhounensis may be loaded with regulatory mechanism diversity and mutation loci related to guanine crystal formation or iridescent cell differentiation. In addition, as a rice-fish culture species, the living environment of C. carpio var. Quanzhounensis harvestmen differ significantly from pond and net-pen culture species, requiring high resistance to disease, adversity, and transport. It is unclear whether the absence of guanine crystals in their skin leads to changes in their basal physiological state, and in-depth studies are beneficial for accurate assessment of culture performance. To reveal the structural basis and transcriptomic characteristics of guanine crystalline deficiency traits in the skin of C. carpio var. Quanzhounensis in this study, we selected the subscale tissues with the most significant differences in guanine crystalline distribution as the control material, and transmission electron microscopy was used to observe th