Do fish breathe oxygen like humans?

DW (English)

All living organisms have to breathe, exchanging oxygen and carbon dioxide with the environment. How do fish do it without lungs? This viewer question comes from Zambia.

Transcript

00:00Do fish breathe oxygen like humans do?

00:08All living organisms have to breathe, exchanging oxygen and carbon dioxide with the environment.

00:17Humans and other animals inhale oxygen because their bodies need it to work.

00:26When you breathe in, your lungs absorb the gas from the air and release it into your

00:32blood.

00:33It carries the oxygen to all parts of your body.

00:37There's also oxygen dissolved in water, but much less of it than in air.

00:44Fish don't have lungs.

00:45Instead, they absorb oxygen from the water with special organs, the gills.

00:52In many fish, the delicate gills lie laterally behind the head and are protected by bony

00:58covers.

00:59They consist of a series of stiff arches covered with filament structures made of thin and

01:04permeable tissue.

01:06The blood flows just beneath the surface of these fine gills.

01:11When a fish opens its mouth, it draws in oxygen dissolved in the water.

01:16When it closes its mouth again, the gill covers open and the water with the oxygen flows over

01:21and past the gills.

01:24The fish can absorb the oxygen from the water via the gills as it flows past.

01:30To do so, they have to be immersed in water.

01:34After absorption, the oxygen is transported all over the body by the blood, just like

01:39in humans.

01:40In the same way, carbon dioxide flows with the blood from the body back to the gills.

01:46Fish can therefore absorb oxygen and release carbon dioxide at the same time.

01:54Not all water has the same amount of oxygen.

01:58Running water contains more of it than standing water like that in a lake.

02:03Fish that live in rivers and brooks, like trout, need more oxygen than other species.

02:12Fish can also breathe through their skin, especially the young animals after hatching.

02:17However, commercial species like cod, loach, and sole can also absorb oxygen through their

02:24skin.

02:25That helps lower the strain on gill respiration and circulation.

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