Fish Ventilation

• 1. Mouth opens (operculum is closed), buccal cavity floor is lowered, increasing volume and decreases the pressure of the buccal cavity compared to the outside so water rushes in the mouth down a pressure gradient
• 2. Opercular cavity expands, buccal cavity is raised, pressure inside the buccal cavity is now higher than in the opercular cavity so water moves from the buccal cavity over the gills into the opercular cavity
• 3. The mouth is now closed and the operculum opens, sides of the opercular cavity move inwards, increasing in pressure and water rushes out of the fish through the operculum