A deeper insight into the deepest vertebrate of the sea

As the deepest vertebrate in the ocean, the hadal snailfish, which lives at a depth of about 7,000m, is a representative case for studying adaptation to extreme environments. Three years after the publication of its first genome, we re-investigated this species using more resequencing individuals and more refined comparative genomic analyses. We found that the hadal snailfish have the ability to migrate across different trenches in the Pacific Ocean after fully adapting to the hadal zone. The loss and retention of sensory genes suggests that the auditory and mechanosensory perception of the hadal snailfish may have undergone compensatory enhancement in complete darkness, while the visual system gradually disappeared. The special environment of the hadal zone has also affected this species in ways that are reflected in genetic changes related to circadian rhythms, behavior, bone mineralization, and high-hydrostatic pressure adaptation. We report here further advances in our understanding of the origin, specific characteristics and adaptive mechanisms of hadal snailfish.