A telomere-to-telomere gap-free genome assembly of the protandrous maroon clownfish (Premnas biaculeatus).

As a protandrous hermaphrodite with natural male-to-female sex change, maroon clownfish (Premnas biaculeatus) serves as an ideal model organism for investigating sequential hermaphroditism. However, genomic resources for this interesting species remain scarce, thereby limiting in-depth research on its unique biological traits. In this study, we generated the first telomere-to-telomere (T2T) gap-free genome assembly of maroon clownfish by integrating multi-platform sequencing data, including MGI short reads, PacBio HiFi long reads, ONT ultra-long reads, and Hi-C sequencing data. The final haplotypic genome spans 884.39 Mb, with all sequences successfully anchored onto 24 chromosomes. This assembly is highly contiguous, with a contig N50 of 37.98 Mb. Comprehensive genomic characterization revealed the precise localization of telomeric repeats and centromeric region within each chromosome. Independent quality assessments, such as QV of 71.01, CRAQ score of 98.98%, and BUSCO completeness of 99.98%, confirmed good assembly accuracy. Additionally, alignment of ONT ultra-long and PacBio HiFi reads to the assembly yielded a high mapping rate exceeding 99%, further validating a good assembly integrity. Repetitive elements constituted 33.51% (296.37 Mb) of the assembled genome, and a total of 24,556 protein-coding genes were annotated. This high-quality T2T genome assembly will not only provide a valuable genetic resource to advance related research in comparative genomics, population genetics, molecular breeding, and functional genomics of maroon clownfish, but also lay a solid foundation for resolving molecular mechanisms underlying its protandrous reproductive strategy.