Genomic signatures of terrestrial adaptation in air-breathing catfishes (Clariidae)

Air-breathing catfishes of the family Clariidae exhibit extraordinary adaptations that enable them to survive outside water for extended periods, yet the genetic and genomic basis of these adaptations remain poorly understood. To study these adaptations, we sequenced and assembled two high-quality genomes of two clariid species, Clarias gariepinus and Clarias dussumieri and compare them with previously available genomes of 23 catfish species across nine families. By reconstructing the whole-genome phylogeny and examining patterns of positive selection and gene family evolution, we found unique signatures associated with terrestrial adaptation in clariids. Our analysis revealed that a high proportion of genes were positively selected in clariids, that play critical roles in hypoxia tolerance, thermoregulation, metabolism, and DNA repair, which are key traits for terrestrial adaptation. Additionally, we observed significant expansions in gene families, including Myoglobin (involved in oxygen transport), immunity-related genes, and xenobiotic degradation pathways, highlighting their importance in environmental resilience and detoxification. Together, these findings provide a comprehensive understanding of the genomic changes facilitating the terrestrial adaptation of clariids. This study also highlights the contribution of genome evolution to their resilience, adaptability to novel environments, and invasiveness, offering valuable insights into the genetic basis of ecological niche diversification.