Chromosome-level genome assembly of the greenfin horse-faced filefish (Thamnaconus septentrionalis) using Oxford Nanopore PromethION sequencing and Hi-C technology

The greenfin horse-faced filefish, Thamnaconus septentrionalis, is a valuable commercial fish species that is widely distributed in the Indo-West Pacific Ocean. It has characteristic blue-green fins, rough skin and spine-like first dorsal fin. T. septentrionalis is of a conservation concern as a result of sharply population decline, and it is an important marine aquaculture fish species in China. The genomic resources of this filefish are lacking and no reference genome has been released. In this study, the first chromosome-level genome of T. septentrionalis was constructed using Nanopore sequencing and Hi-C technology. A total of 50.95 Gb polished Nanopore sequence were generated and were assembled to 474.31 Mb genome, accounting for 96.45% of the estimated genome size of this filefish. The assembled genome contained only 242 contigs, and the achieved contig N50 was 22.46 Mb, reaching a surprising high level among all the sequenced fish species. Hi-C scaffolding of the genome resulted in 20 pseudo-chromosomes containing 99.44% of the total assembled sequences. The genome contained 67.35 Mb repeat sequences, accounting for 14.2% of the assembly. A total of 22,067 protein-coding genes were predicted, of which 94.82% were successfully annotated with putative functions. Furthermore, a phylogenetic tree was constructed using 1,872 single-copy gene families and 67 unique gene families were identified in the filefish genome. This high quality assembled genome will be a valuable genomic resource for understanding the biological characteristics and for facilitating breeding of T. septentrionalis.