Betta fish opening their gill covers is a normal physiological behavior, primarily associated with the following functions:
Respiratory Function
Betta fish absorb dissolved oxygen in water through their gills. Opening the gill covers increases the contact area with water, thereby enhancing respiratory efficiency. Their unique labyrinth organ (such as the suprabranchial organ in paradise fish) allows them to directly extract oxygen from air, enabling them to adapt to low-oxygen environments.
Excretion of Metabolic Wastes
Gills are not only respiratory organs but also play a role in excreting metabolic wastes like ammonia and nitrogen from the body, helping to maintain fluid balance.
Behavioral Displays
Deterring Rivals: When male bettas encounter conspecifics or their own reflection in a mirror, they will puff out their gills to display their size and deter the opponent.
Courting Mates: During the breeding season, males use exaggerated gill movements to attract females.
Notes
If a betta fish keeps opening its gills abnormally, accompanied by darkening body color or swollen gill filaments, it may indicate a disease (such as gill rot or parasitic infection), and prompt intervention is necessary.