In steps, how do fish exchange gas?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Fishes exchange gases by using gills. Here is a step by step procedure:

  • The alternate opening of mouth and operculum (thin layer covering the gills) forces the water (saturated with oxygen) over the gills.
  • Gills contain gill filaments, which provide them with very large surface area. Filaments contain a large number of protrusions called lamella. 
  • Counter-current flow of blood and water ensures gas exchange between the two fluids. As the oxygen-deficient blood flows, it comes in contact with oxygen-saturated water and this dissolved oxygen diffuses into the blood by diffusion.
  • Similar to oxygen diffusion into blood, carbon dioxide diffusion into water takes place. The blood is rich in carbon dioxide, whereas the water is deficient in it, this sets up a concentration gradient that causes diffusion of carbon dioxide into the water.
  • The carbon dioxide containing water exits through the lungs.

Hope this helps.

Approved by eNotes Editorial Team

We’ll help your grades soar

Start your 48-hour free trial and unlock all the summaries, Q&A, and analyses you need to get better grades now.

  • 30,000+ book summaries
  • 20% study tools discount
  • Ad-free content
  • PDF downloads
  • 300,000+ answers
  • 5-star customer support
Start your 48-Hour Free Trial