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🐟 How do fish breathe underwater

Understand how water moves over gills, how oxygen diffuses into blood, and why countercurrent exchange is efficient.

2
lessons
~10 min
to learn
Adults
level
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What you’ll learn

  1. The gill pumpExplain how mouth and operculum movements drive water across the gills.Fish use a one-way pump to bring water into the mouth, over protected filaments, and out beneath the gill cover.
  2. Diffusion does the exchangeDescribe how thin lamellae and countercurrent flow move oxygen into blood and carbon dioxide out.Diffusion across a large, thin surface supplies the body, while opposite water and blood flows preserve the oxygen gradient.

Questions this course answers

What is the main job of the mouth and operculum together?

Their coordinated movements drive a continuous flow of water across the gills.

Why do gills have filaments and lamellae?

The many folds and plates provide lots of contact area for diffusion while staying compact.

What moves from water into a fish's blood at the gills?

Oxygen already dissolved in the water diffuses across the thin lamellae into blood.

Why is countercurrent flow useful?

Opposite directions keep blood meeting water with a higher oxygen concentration throughout the exchange surface.

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