Fish use gills to extract oxygen from water to survive

All animals need oxygen to survive - even if they spend their lives in water.

Humans and terrestrial animals inhale air, which is a mix of many gasses and 20 percent of that is oxygen.

The process begins when the nose inhales air. Air is pushed through the windpipe to the lungs. Red blood cells pick up oxygen and flow throughout the circulatory system to deliver it to organs. On the exhale, the body pushes out carbon dioxide.

Aquatic animals are similar to humans in that they, too, require oxygen to survive.

Oxygen, in the form of dissolved oxygen, is found in fresh water and salt water. The levels of dissolved oxygen can change depending on the water's temperature, depth and the presence of harmful chemicals and bacteria levels.

Different bodies of water have different oxygen saturation levels; animals have differing requirements for the amount of dissolved oxygen needed.

Fish, crustaceans and worms have gills in place of lungs. The process begins when a fish opens its mouth underwater. Instead of a nose and windpipe, fish gills carefully extract oxygen from water. Gills are a network of filaments designed to capture dissolved oxygen and dispense it throughout the fish's body.

Like in humans, carbon dioxide is separated from the mix and pushed out. Water has only about a 5 percent oxygen level at best, so it's important that streams, rivers, lakes and oceans are kept clean to provide optimal dissolved oxygen levels for fish and other aquatic life to remain healthy.

Factors that can stand in the way of strong dissolved oxygen levels include higher water temperatures and too much nutrient from fertilizer runoff that can cause algal blooms that consume oxygen. Chemical additives from storm sewer overflows and dumping can cause water quality, and oxygen levels, to plummet.

Many organizations monitor fresh and salt water bodies to make sure dissolved oxygen levels are healthy.

In Illinois, there are 87,000 miles of rivers and streams. You can help keep these waterways clean by staging a cleanup with friends or by joining an organization that monitors waterway health.

Trout Unlimited is a national group of volunteers that works to keep waterways clean. Locally, Friends of the Chicago River works throughout the year to keep the Chicago River, its feeder streams and surrounding plant and animal life healthy. On Saturday, May 13, the group hosted its 25th Chicago River Day cleanup.

John Quail, director of watershed planning for the organization, said the river and streams have seen improvements since fish populations hit a low 30 years ago.

"It's more diverse and robust," Quail said, with as many as 72 species currently living in the Chicago River.

While water quality in general is good, there are spots where it can be improved. Groups are focusing on the North Shore channel, which incorporates reclaimed water and flows as far north as Wilmette.

"There are a number of ways to improve water quality, including restoring native vegetation, letting the water flow over rocks for aeration, adding aeration stations like the one at Webster in Chicago, and elevated aeration stations like one in the Calumet system," Quail said.

Find out more about the work Friends of the Chicago River does at www.chicagoriver.org.

Check it out

The Schaumburg Township District Library suggest these titles on fish:

• "Fish Tricks: the Wild & Wacky World of Fish" by Haude Levesque

• "Eyewitness Fish" by Steve Parker

• "Fish" by Christine Taylor-Butler