Expiration and inspiration

• Expiration 1

  muscles contract to close the mouth - muscles around buccal cavity contract to increase pressure - operculum open and water forced out over gills due to buccal pressure pump
• Expiration 2

  Operculum centre moves in which decreases volume and increases pressure but this is still lower than buffaloes pressure so water flows out over gills
• Inspiration 3

  muscles around buccal cavity relax and lower its floor - increases volume and decreases pressure in buffalo cavity - when it’s zero the mouth has opened - decrease in pressure allows water to enter - operculum closed
• Inspiration 4

  Operculum closed but centre raised up and out - decreasing pressure - water flows into the gills due to pulling action of operculum suction pump
• Some fast swimming fish like tuna always keep their mouth open and rely on water pressure from swimming to force water into gills
• Ram ventilation

  pumo and valve mechanism not required - energy saving