Experiment, Rivers, Seas and Oceans

How do fishes breathe?

How does it happen that some animals, like most fishes, but also water molluscas (e.g. clams and octopuses), crustations (e.g. crayfishes, crabs), can breathe under water? They have gills. This organs are located on both sides of the animals throat and are made of multiple plates. Some animals opens and closes their snout and gill covers, pumping oxygenated water into the respiratory organs. Some of the water movements through gills is caused by animals fast swimming. Water with oxygen, enters the mouth, next, it pours out in between the gill plates outside. Before it happens tough, oxygen from water enters the animals blood, and carbon dioxide exits into the water, that will pour out of fishes body later.

To understand it better, let’s do a little experiment.


  • Explaining to kids how do fishes breathe


Time: 15 minutes

01.jak Oddychaja Ryby 08.06


    • Coffee filter
    • Ground coffee or coffee grounds
    • Two glasses
    • Water

Task flow

  1. Pour water with coffee grounds into the first glass
  2. Put a coffee filter into the other glass
  3. Pour the water with coffee grounds through the filter

Coffee filter represents the gills and the coffee grounds represent the oxygen that a fish needs. Similarly to a coffee filter separating water from coffee grounds, gills collect oxygen to send it to fishes cells. A fish collects water through mouth and transports it through gills, where oxygen can get dissolved and pushed into the blood.

14.11 Dzien Czystego Powietrza 1 E1668703355599

This post was created as part of a project co-financed by Deutsche Bundesstiftung Umwelt in cooperation with Naturschutzzentrum Oberlausitzer Bergland.