Oxygen in water is known as dissolved oxygen or DO.
Oxygen is constantly entering and leaving water, but there is a certain amount of oxygen in water at all times. This is because water has a natural attraction to oxygen. When oxygen comes in contact with the surface of water, the oxygen enters the water, becoming dissolved oxygen.
There are three main sources of oxygen in the natural aquatic environment:
A concentration of five parts per million (ppm) (=
or higher is recommended for optimum fish health.
The amount of attraction between oxygen and water depends on the
amount of oxygen already in the water. If there is very little oxygen
in water, then the water is very attractive to oxygen. But when water
has a high concentration of DO, then the water is saturated,
meaning that the water contains as much oxygen as it can hold.
A fish's metabolism also helps determine the amount of oxygen which a fish needs to survive. Fish with a high metabolism are fast-moving but also require a great deal of oxygen to survive. Fish with a slow metabolism are more sluggish and require less oxygen.
Carp for an example which is a warm water fish can survive in water with as little as 3 ppm of oxygen, while largemouth bass require 5 to 8 ppm.