Evaluating the Air Respiratory Capacity of Awaous (Chonophorus) tajasica (Gobiiformes: Oxudercidae): A Morpho‐Functional Study

Surface air-gulping behavior has been reported in several gobiid fishes, but its contribution to oxygen uptake remains unclear. This study aimed to evaluate the air-breathing capacity of Awaous tajasica through behavioral observations, measurement of oxygen consumption, and analysis of the functional morphology of its palate and gills. Behavioral observations demonstrated that under hypoxic conditions, the fish moved to the water surface to engulf air bubbles, which remained within the buccal cavity during aquatic gill ventilation before being expelled through an opercular cavity. Oxygen consumption analysis revealed that A. tajasica obtained approximately 70% of its oxygen from the water and 30% from atmospheric air when under low aquatic oxygen conditions. Palate morphology did not reveal specialized respiratory structures, and only typical sensory structures such as taste buds were observed, indicating the absence of a dedicated aerial exchange surface. The retention of an air bubble in the buccal cavity during low aquatic oxygen concentration supports a functional contribution of air gulping to oxygen uptake in A. tajasica, demonstrating aerial oxygen acquisition without specialized air breathing organs in this gobiid species.