4 Conclusions
Wrasses are marine fish, and the humphead wrasse is an endangered species that plays an important role in maintaining the stability of reef ecology. Due to the lack of high-quality and high-continuity reference genomes, the understanding and conservation efforts of this species remain limited. In this study, we first present a draft genome assembly of the humphead wrasse generated via Nanopore long read sequencing, achieving a 1173.4 Mb genome with a contig N50 length of 16.5 Mb based on raw reads of 90.7 Gb, a 77-fold coverage of the genome. Using Hi-C sequencing technology, the raw reads that represented a 124-fold coverage of the genome anchored into 24 chromosomes and produced a genome size of 1173.2 Mb with a contig N50 length of 3.7 Mb and a scaffold N50 length of 51.5 Mb. The genome was annotated with 22,180 functional genes and 97% of the complete BUSCO genes. Transposable elements accounted for 39.88% of the entire genome. Comparisons with other fishes reveal that a larger genome correlates with increased content of transposable elements. A specialized feature of the united jawbone, which increased the ability to manipulate food, allows us to investigate the functional morphology of this species in visual clues. We have found a sudden increase in number of opsins, SWS2 , LWS 1, andRh2, in tandem pattern by comparative genomics, possibly highlighting alternative adaptation after gene duplication. The increased opsin copies were specific for the humphead wrasse, owing to gene conversion, which was contributed by the uneven distribution of transposable elements in a special genome region. The divergent expression of opsin in the retina indicated visual plasticity for function divergence in efficient foraging, transition into adulthood, specific mate-searching behavior, sexual reversal, and reproduction of this species. The chromosome-level genome assembly of humphead wrasse will provide valuable resources to further understand behavior, gene fluidity, and evolution in fishes.