Skip to content
KinPilot™Learn & Explore
Menu
← TopicsReading path →

Grades K–2 · Organisms

How do fish gills take oxygen from water?

A fish can stay underwater while getting oxygen its body needs. It uses gills. Water enters the mouth, passes over the gills and leaves through an opening behind the head.

O29 visual explanationAcross gill surface in one schematic fish. Water enters the mouth, passes over gills and leaves; dissolved oxygen can cross toward blood. Oxygen dots are symbols, not visible bubbles or oxygen made by splitting water.Gills take dissolved oxygen from waterFish with gill coverGill close-upWaterBloodAcross gill surfaceOxygen is already dissolved in the water.

In the diagramGills take dissolved oxygen from waterFish with gill coverGill close-upWaterBloodAcross gill surfaceOxygen is already dissolved in the water.

Water passes over the gills while dissolved oxygen crosses toward the blood. The dots represent oxygen already in the water, not visible bubbles.

There is oxygen already mixed into the water. This is called dissolved oxygen. The oxygen is invisible; colored dots in a drawing only stand for it. At the gills, some of that oxygen moves from the water into the fish's blood. The gills do not turn water into oxygen.

The blood carries oxygen onward through the body, while the water continues out past the gills. More water arriving brings more dissolved oxygen near the gill surface. Fish move water over their gills in different ways, but this connection between moving water and flowing blood helps explain how a fish gets oxygen without taking a breath of air.

About this explanation

Starting knowledge: Recognize a fish and understand that water can flow past a body part.

Sources

  • NOAA Library — Gills for Breathing
  • NOAA Fisheries — Fun Facts About Fascinating Fish
← Grades K–2 topics