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…