Bony fish

• How do bony fish exchange gases?

  Gas exchange happens in the water and the gills are used to absorb oxygen and release carbon dioxide into the water.

  Most bony fish have 5 pairs of gills which are covered by a bony plate called operculum.
• Gill plate structure?

  Each gill consists of two rows of gill filaments attached to the bone arch. The filaments are very thin and are folded into lamellae (gill plates), this provides a large surface area. Blood capillaries carry deoxygenated blood close to the surface of the gill plates where exchange takes place.
• Countercurrent flow?

  Blood flows through the capillaries in the opposite direction to the water flow over the lamellae (gill plates). This creates a counter current flow which allows maximum oxygen absorption from the water
• Ventilation in bony fish?

  Bony fish keep water flowing through their gills by using a buccal - opercular pump. The buccal cavity (mouth) can increase in volume if the floor of the mouth moves down allowing water to enter the buccal cavity. The mouth closes and the floor of the mouth moves up again pushing the water through the the gills. As water is pushed from the buccal cavity, the operculum moves outwards reducing the pressure to allow the water to flow over the gills.