Clarias batrachus Genome sequencing and assembly

Walking catfish (Clarias batrachus) are freshwater fish capable of air-breathing and locomotion on land. It usually inhabits various low-oxygen habitats, burrows inside the mudflat and sometimes “walks” out of current places to search suitable environments during summer. Obviously, it has evolved with accessory air-breathing organs for respiring air and corresponding mechanism to survive in such derelict environments. Thereby it serves as a great model for understanding adaptations to terrestrial life. Comparative genomics with non-air-breathing fishes suggested its adaptive evolution and other genomic signatures for terrestrial adaptation. Additionally, we sequenced and compared the transcriptomes of the gill and the air-breathing organ to demonstrate the mechanism of aerial respiration involved in elastic fiber formation, oxygen binding and transport, angiogenesis, ion homeostasis and acid-base balance. This study provides an important genomic resource for understanding the adaptive mechanisms of walking catfish. It is apparent that the coupling of enhanced abilities in oxygen transport and oxygen storage through genomic expansion of myoglobin and transcriptomic up-regulation of hemoglobin is an important component of the molecular basis for the adaptation of this aquatic species to terrestrial life.