Gas Exchange in Fish


Gas Exchange in Bony Fish - bony fish covered in scales - no gas exchange through surface, contain gills in the opercular cavity

Water -  about 30x less oxygen than air, denser than air, more viscous 

Breathing in fish 

To take in water:

  • mouth opens
  • operculum (gill cover) closes
  • floor of mouth cavity lowered - increasing volume inside cavity - causes pressure to fall
  • water flows into mouth as pressure inside now lower than outside 

To let water out: 

  • mouth closes
  • floor of mouth cavity raised - decreasing volume inside cavity - pressure rises
  • operculum opens 
  • water flows out through operculum - pressure inside now higher than outside fish 

Gills - four pais in pharynx (throat), each gill supported by bony gill arch, each gill…


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