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.