Which part of the gill of fish is involved in gaseous exchange?

The part of the gill of a fish that is involved in gaseous exchange is the gill filament. Gill filaments are thin and thread-like structures that project from the gill arches. They are covered with tiny finger-like projections called lamellae, which are rich in blood vessels. As water flows over the lamellae, oxygen diffuses from the water into the blood vessels, and carbon dioxide diffuses from the blood vessels into the water. This exchange of gases is facilitated by the thin walls of the gill filaments, which provide a large surface area for gas exchange to occur.