9 Air Breathing in Fishes

Abstract

Publisher Summary Structural adaptations for air breathing in fishes are extremely diverse. The extent of modifications from structures typical of an aquatic breather usually reflects the relative role of air breathing in overall gas exchange. Some species rely predominantly on water breathing with gills and only supplement gas exchange with air breathing when adverse respiratory qualities in the water make aquatic breathing insufficient or too costly for extraction of the required oxygen. Others obligate air breathers and succumb if denied access to air for a short time. Most air-breathing fishes are teleosts but typically the dipnoan, chondrostean, and holostean fishes are dominated by air-breathing forms. Reports of air-breathing habits among elasmobranch fishes have not been adequately confirmed. A smaller number of air-breathing fishes live in temperate regions, and in exceptional cases such as the bowfin, Amiu calva , they occupy waters seasonally frozen over. A shortage of dissolved oxygen constitutes the primary environmental condition that has stimulated the development of air-breathing in fishes, although such adaptations may also have been correlated with behavior or activity patterns. Among air-breathing fishes, those occupying brackish and marine habitats are rare because of the well-stirred turbulent conditions of these waters. However, several members of marine gobiid and blennid families show structural adaptations for air breathing. Estuarine waters may show large spatial, diurnal, and seasonal fluctuations in oxygen availability. More exceptionally, fishes like Periopthalmus have developed air-breathing habits in support of behavioral acts such as feeding and escape reactions.