Breathing underwater: Lakes

What are you doing Leon? - I’m looking at my new goldfish. It keeps opening its mouth. It looks like it’s talking. It’s not talking Leon, it’s breathing. Fish can’t breathe like we do because they live in water.

But they still need oxygen to live. There is less oxygen in water than in air. This is why fish need different ways and special body parts in order to get oxygen from water. The fish opens its mouth, water flows in, and then flows through this part of the fish. It’s bright red, and looks like feathers.

It’s a GILL. Gills are red because they are full of small blood vessels. So what happens when water passes through the gills? There are thousands of water channels in there, surrounded by blood vessels. Oxygen easily moves from where there’s a lot of it, to where there’s less of it.

Because there is less oxygen in blood than in water, oxygen will move from water into blood. This is called diffusion. The blood then carries the oxygen around the body. But fish are not the only animals that have gills. Many different insects that live near lakes and rivers also have gills.

Like this young mayfly. It’s so young that it does not have wings yet, and still lives in water: it’s a larva. Insect gills grow outside the body. They look like feathers and are not covered by anything - so oxygen gets in easily! Insect gills do not have blood vessels like fish gills.

They have air tubes called trachea. Insects breathe because of trachea. This type of breathing is called TRACHEAL BREATHING. Just like in fish gills, oxygen will easily move into trachea because there is less oxygen there than in water. Gills like this that grow out from the body are called TRACHEAL GILLS.

Leon doesn’t have gills. So he can’t breathe underwater. But with a mask and a snorkel he can! Leon is not the only one with a snorkel. Insects like mosquitoes lay their eggs in water.

When a young mosquito leaves its egg, it’s also called a larva. Mosquito larvae stay in the water for days, but they need oxygen. They have a special air tube at the end of their body, that looks a little bit like Leon’s snorkel. It’s a SIPHON. The siphon sticks out of the water and opens up to the air.

That’s how the larvae get oxygen. Breathing through the siphon is another way of TRACHEAL BREATHING. - Sometimes there are red worms in the puddles in the park. But they are so small, do they also breathe with gills or siphons? Good question, Leon. Actually, these red worms are the midge larvae, another type of insect.

But they don’t have gills, nor a siphon. They breathe through their skin. These larvae have transparent skin. This is why they look red - the colour of the blood cells shows through! The skin of the larva is very thin, and there’s a lot less oxygen inside its body than in the water.

This is why oxygen easily moves - diffuses - into its body. Breathing through skin like this is called CUTANEOUS BREATHING. Breathing with gills, tracheal breathing, and cutaneous breathing are different ways in which animals breathe underwater. - I wish I could breathe underwater too. But with my mask and snorkel I can almost do it!