Chromosome-level assembly of Southern catfish (Silurus meridionalis) provides insights into visual adaptation to the nocturnal and benthic lifestyles

Southern catfish (Silurus meridionalis) is a nocturnal and benthic freshwater fish endemic to the Yangtze River and its tributaries with an important economic value but a drastically declining wild population. In this study, we constructed a chromosome-level draft genome of S. meridionalis using 69.7 Gb Nanopore long reads and 49.5 Gb Illumina short reads. The genome assembly was 741.2 Mb in size with a contig N50 of 13.19 Mb. An additional 116.4 Gb of Bionano and 77.4 Gb of Hi-C data were applied to assemble contigs into scaffolds and further into 29 chromosomes, resulting in a 738.9 Mb genome with a scaffold N50 of 28.04 Mb. A total of 22,965 protein-coding genes were predicted from the genome with 22,519 (98.06%) genes functionally annotated. Comparative genomic and transcriptomic analyses revealed that catfish possess a rod-dominated visual system which is responsible for scotopic vision. The absence of cone opsins SWS1 and SWS2 resulted in the lack of UV and violet sensitivity. Mut...