 |
|
Vital Signs
To breathe underwater, fish require microscopic bubbles of oxygen called dissolved oxygen. These bubbles pass over their gills, a bunch of tiny flaps behind their heads. Gills collect oxygen in water and let out carbon dioxide.
In rare cases, DO concentrations can become too high and cause "gas bubble disease." Far more common, however, are oxygen levels that are too low. |
© WCS |
Dissolved oxygen levels are measured in milligrams per liter (mg/L) or parts per million (ppm). When they drop below 5 mg/l or ppm, fish are put under stress. The lower the concentration, the greater the stress.
Dissolved-oxygen levels that remain below 1-2 mg/l for a few hours can lead to large fish kills.
 |
|
 |
|
|
1. What signs of stress do you observe when DO falls
below 5 ppm?
2. How do the fish differ in general at higher and lower
levels of DO? |
|
|
 |
|
 |
back to top
© 2004 Wildlife Conservation Society.
|
