Cartilaginous fish respire using what structure?

Cartilaginous fish respire using what structure?

• A. Lungs
• B. Gills
• C. Skin
• D. Tracheae

Answer: (B)

Cartilaginous fish respire primarily through gills. Water flows over the gill filaments, where thin membranes with a rich capillary network enable gas exchange: oxygen diffuses into the blood and carbon dioxide diffuses out. The arrangement, often countercurrent, keeps a favorable oxygen gradient along the entire gill, making oxygen uptake efficient even when water doesn’t carry much dissolved oxygen. Lungs aren’t present in these fish, so they don’t use air-breathing organs. The skin can contribute a little gas exchange in some species, but it’s not the main source of respiration. Tracheae are part of insect respiration, not fish.

Cartilaginous fish respire primarily through gills. Water flows over the gill filaments, where thin membranes with a rich capillary network enable gas exchange: oxygen diffuses into the blood and carbon dioxide diffuses out. The arrangement, often countercurrent, keeps a favorable oxygen gradient along the entire gill, making oxygen uptake efficient even when water doesn’t carry much dissolved oxygen. Lungs aren’t present in these fish, so they don’t use air-breathing organs. The skin can contribute a little gas exchange in some species, but it’s not the main source of respiration. Tracheae are part of insect respiration, not fish.