Air ventilation by recoil aspiration in polypterid fishes.

High-speed x-ray cine films synchronized with intra-pleuroperitoneal pressure measurements show that polypterid fishes aspiration breathe by the deformation and recoil of their bony-scaled integument. Paleozoic amphibians arose from ancient air-breathing fishes and retained piscine bony scales in V-shaped rows along the belly. These scales resemble those of modern polypterid fishes and may have contributed to inhalation by elastic recoil. The discovery that polypterid fishes breathe by recoil aspiration is the first evidence for aspiration breathing in any lower vertebrate. The use of recoil aspiration by polypterids shows that elastic storage in a stiff body wall can contribute to inhalation in animals with limited capacity for active aspiration.