Which organ plays a role in gaseous exchange in fishes? 

Gills are essential for gaseous exchange in fish. Fish are aquatic animals with no lungs, so they must extract oxygen from the water in which they live. 

Gills are specialized structures that extract dissolved oxygen from water and exchange it for carbon dioxide, which is then expelled back into the water. 

The gills have a large surface area with many thin filaments and lamellae, providing a large surface area for gas exchange. 

The movement of water over the gills contributes to an increase in the concentration gradient of oxygen, facilitating oxygen uptake by the blood. The gills also help to remove waste products from the fish's body, such as carbon dioxide.