ABSTRACT
Many osteichthyan fishes obtain oxygen from both air, using a lung, and water, using gills. Although it is commonly thought that fishes air-breathe to survive hypoxic aquatic habitats, other reasons may be more important in many species. This study was undertaken to determine the significance of air-breathing in two fish species while exercising in oxygen-rich water. Oxygen consumption from air and water was measured during mild activity in bowfin (Amia calva) and spotted gar (Lepisosteus oculatus) by sealing a fish in an acrylic flume that contained an air-hole. At 19–23°C, the rate of oxygen consumption from air in both species was modest at rest. During low-level exercise, more than 50% of the oxygen consumed by both species was from the air (53.0±22.9% L. oculatus; 66.4±8.3% A. calva).
