How Do Fish Breathe?
Fish primarily breathe through gills, which are specialized organs that extract dissolved oxygen from water. The gills are located behind and to the side of the mouth cavity and consist of fleshy filaments supported by bony gill arches. The filaments are rich in blood vessels and provide a large surface area for gas exchange. As water flows over the gill filaments, oxygen is absorbed into the blood, and carbon dioxide is expelled back into the water. This process is efficient due to the proximity of blood capillaries to the gill surface, ensuring effective gas exchange.
Lungfishes possess primitive lungs derived from the swim bladder, allowing them to survive in oxygen-poor waters by gulping air at the surface. The swim bladder, originally a hydrostatic organ (an organ used for buoyancy in most bony fish), has evolved in some species to become a vascularized accessory breathing organ.
Electric eels rely on air breathing. They live in warm, oxygen-poor freshwater and surface regularly to gulp air. Their mouths are highly vascularized and serve as the main site for gas exchange, while their gills are used primarily to expel carbon dioxide. Labyrinth fish, including Siamese fighting fish and gourami, have a labyrinth organ that functions like a rudimentary lung, allowing them to extract oxygen directly from the air. These adaptations highlight the evolutionary diversity among fish, enabling them to thrive in a wide range of aquatic habitats.