Gills of bony fishes

• In bony fishes gills are covered with an operculum that is made of flattened skeletal plates and there is no spiracle as in elasmobranchs.
• There are 4 pairs of gill pouches, each containing two demibranchs, making the total number of demibranchs in bony fishes as 8 pairs or four pairs of complete gills or holobranchs.
• Teleosts always breathe with their mouth open and eject expiratory water by opening operculum.
• Gills in Chondrostei, Holostei and the lungfish Neoceratodus exhibit partial reduction in their interbranchial septa, which happens to be somewhat intermediate condition between elasmobranchs and teleosts.