Respiration

February 5, 2025

All sharks have 5-7 gill slits. Each gill arch contains feathery looking gill filaments, made up of small leaf-like lamellae which contain capillaries. As blood flows through these in one direction and water flows across the gills in the opposite direction (the counter-current principle), oxygen diffuses from its high concentration in the water to the lower concentration in the blood with carbon dioxide passing in the opposite direction.

Some sharks are termed ‘obligate ram ventilators’ which means they must maintain a certain swimming speed to keep breathing, whereas other species are capable of ‘buccal pumping’ and use muscles to actively move water across their gills. This is often aided by the spiracles, located behind the eyes, which are modified gill slits that allow oxygenated water to be drawn in when sharks are feeding or resting on the seabed.