An Evolutionary Perspective for Bimodal Respiration: A Biological Synthesis of Fish Air Breathing

SYNOPSIS: The broad phyletic distribution of bimodal breathing among the fishes, the diversity of this group's aerial-respiratory specializations, and the numerous ways that bimodality has permeated the natural history of many species provide a broad perspective on the evolution and biological significance of bimodal breathing. The long term evolutionary view of bimodal breathing emphasizes its importance in the evolutionary transition to terrestriality; a key role in this process was played by the fishes which were the first air-breathing vertebrates. On the other hand, in most extant fishes bimodality has not led to terrestriality. Rather, auxiliary air breathing enables a species to remain in or to exploit an aquatic habitat from which it would otherwise be excluded.