The telomere-to-telomere gapless genome of grass carp provides insights for genetic improvement

Abstract Background The grass carp (Ctenopharyngodon idella) is a large herbivorous freshwater fish belonging to the Cyprinidae family. It is widely cultivated as a food source in China and is renowned as one of the Four Great Domestic Fishes. Despite its economic importance, the published genome assemblies of grass carp remain incomplete due to gaps, thereby hindering molecular research and genetic improvement. Results In this study, we report the assembly of a telomere-to-telomere (T2T) gap-free genome of the grass carp with total length of 890,918,310 bp for 24 chromosomes without gaps, representing the highest completeness and assembly quality to date. Our assembly contains 27,446 protein-coding genes, and 93.04% of all were annotated with multiple databases, with 48 telomeres and 24 centromeres characterized. Gap-free reference genomes enable us to study the structure of centromeres and identify conserved centromere-specific satellite motifs for grass carp. Furthermore, we identified 108 gene-related gaps across 12 chromosomes and 38 structural variations across 17 chromosomes in this T2T assembly. Conclusions The validated gap-free genome provides invaluable resource for future genomic studies grass carp, offering new insights into its genetic architecture and evolutionary dynamics.