What Are Structures That Help Fish Get Oxygen From Water?

Gills

• A gill is a respiratory organ and the gill structures are visible on a fish. You can see the gills dangling in open water. Through the gills, gases are exchanged between the fish and the surrounding water.

Filaments

• The gills have a large area for gas exchange and this helps the fish to absorb oxygen from the water and give off carbon dioxide. Gills consist of thin filaments of tissue and the highly folded surface of the branches increases the surface area. This is important since water contains less dissolved oxygen than air does and a large area means that more oxygen can be exchanged.

Oxygen Dissovled in Water

• Water molecules can be broken up into hydrogen and oxygen. However, the gills absorb the oxygen that is dissolved in the water. The gills do not break water into hydrogen and oxygen molecules. Water is constantly passing into the body of a fish and the outside water is diluting the high concentration of salts in the fish. A fish does not need to drink water to keep the salts in the body diluted.

Pumping in Water

• A fish breathes by drawing in water. A fish is opening and closing its mouth and pumping water back to the gills. The fish forces the sides of its throat together, and the water runs through openings in the gills. The gill slits, operculum, may be the evolutionary ancestors of the tonsils. The outer covers of the gills closes when the fish opens its mouth. The gill slits open when the fish closes its mouth, allowing water to cross the gills. Some fish, such as tuna, have to swim constantly since their pumping system is less effective. The fish is swimming to make sure that the gills are getting oxygenated water.