Chapter 2 - Diversity and Natural History

Abstract

This chapter provides information on geographical distribution, ecology, and habitats of the air-breathing fishes. Air breathing is common among the primitive families but has often been acquired independently by the more modern families. In different families, air breathing ranges from rare-to-common-to-universal. This chapter offers details about air-breathing organ (ABO) structure, air-breathing behavior and physiology, and whether or not air breathing is obligatory. The chapter also describes diverse approaches brought to the study of air breathing in different species in order to bring to light the full spectrum of ideas and information embodied in this area of research. The chapter summarizes air-breathing fish diversity and discusses the species for which this specialization has been reported but not fully documented. The chapter suggests that categorizations of fishes based on ABO structure cannot differentiate homologous structures, as many air-breathing fishes lack ABOs. Therefore, a classification of the air-breathing fishes must be sufficiently broad to allow considerations of ABO structure and permit estimation of air-breathing fish diversity and the frequency of the independent origin of this specialization.