Genome of the butterfly hillstream loach provides insights into adaptations to torrential mountain stream life

Chromosome-level genome assembly of the butterfly hillstream loach Beaufortia pingi

The Butterfly hillstream loach (Beaufortia pingi), an aquatic benthic fish species inhabiting mountain rapids, exhibits exceptional capabilities in movement, adsorption, and desorption processes, enabling it to adhere to smooth and contaminated surfaces in turbulent streams. These attributes make it a significant subject for genetic and evolutionary research. In this study, the genomic sequences of this species were acquired utilizing PacBio sequencing and Hi-C methods. The genome assembly is 459.8 Mb in size with a contig N50 of 5.35 Mb, and the assembled contigs were anchored into 25 chromosomes. BUSCO analysis confirmed a high completeness level with 97.0% gene coverage. A total of 111.47 Mb repetitive sequences (24.25% of the assembled genome), and 22,906 protein-coding genes were identified in the genome. This study represents the first investigation of the species' genome. The establishment of this genome assembly provides valuable resources for future genetic research and facilitates the study of genetic changes during evolution.

Genomic insights into the seawater adaptation in Cyprinidae

BACKGROUND

Cyprinidae, the largest fish family, encompasses approximately 367 genera and 3006 species. While they exhibit remarkable adaptability to diverse aquatic environments, it is exceptionally rare to find them in seawater, with the Far Eastern daces being of few exceptions. Therefore, the Far Eastern daces serve as a valuable model for studying the genetic mechanisms underlying seawater adaptation in Cyprinidae.

RESULTS

Here, we sequenced the chromosome-level genomes of two Far Eastern daces (Pseudaspius brandtii and P. hakonensis), the two known cyprinid fishes found in seawater, and performed comparative genomic analyses to investigate their genetic mechanism of seawater adaptation. Demographic history reconstruction of the two species reveals that their population dynamics are correlated with the glacial-interglacial cycles and sea level changes. Genomic analyses identified Pseudaspius-specific genetic innovations related to seawater adaptation, including positively selected genes, rapidly evolving genes, and conserved non-coding elements (CNEs). Functional assays of Pseudaspius-specific variants of the prolactin (prl) gene showed enhanced cell adaptation to greater osmolarity. Functional assays of Pseudaspius specific CNEs near atg7 and usp45 genes suggest that they exhibit higher promoter activity and significantly induced at high osmolarity.

CONCLUSIONS

Our results reveal the genome-wide evidence for the evolutionary adaptation of cyprinid fishes to seawater, offering valuable insights into the molecular mechanisms supporting the survival of migratory fish in marine environments. These findings are significant as they contribute to our understanding of how cyprinid fishes navigate and thrive in diverse aquatic habitats, providing useful implications for the conservation and management of marine ecosystems.