Do fish get thirsty?

How was your half-term break?

Here at Life, we had thousands of visitors from all over the country. Throughout the week, we were challenged with lots of great questions by curious visitors! Why is the sky blue? Are teeth the same as bones? Where are the toilets?

Here are two questions that left me completely stumped.

Sardines school in a underwater shoot at the shore line.“Do fish get thirsty?”
Jacob – eight years old

This question caught me quite off guard, but let’s think about it. Would you feel hungry if you lived in a stottie? No, probably not… But this is not a very scientific way of looking at the world, so let’s break down the question.

First, what do we mean by thirst? Humans can feel thirsty for lots of reasons, including extreme heat, salty or spicy food, anxiety and certain illnesses. Thirst is the brain’s way of telling us that we are dehydrated or in danger of dehydration and to get a glass of water.

So what about fish? Unlike us, fish don’t need to actively find water, they’re surrounded by it!

Freshwater fish stay hydrated by absorbing water directly through their skin without even having to think about it. This is a process called osmosis. Fresh water from lakes or fish bowls will naturally flow into the saltier water inside the fish’s body.

A saltwater fish, on the other hand, has a lower salt concentration in its body than the water around it. To make up for the water that it loses out of its skin trough osmosis, it is constantly gulping down water. Like the beating of our heart, it’s unconscious and so requires no active thinking.

So do fish feel thirsty? Until we can learn to speak Fish, we will never really know. But based on what we DO know, we can say with a high degree of certainty that, no, fish don’t feel thirsty.

Earth Changing Season Vector Illustration

“What was the first season on the Earth?”
Kirsty – six years old

I love this type of chicken and egg question – but wow, I wasn’t even sure where to start!

Let’s go right back to the beginning. About 4.6 billion years ago, the Earth was a giant ball of explosive red hot lava, with no seas and no land masses. Very, very slowly, over millions of years, the Earth cooled to develop its crust, puddles became oceans and the seasons began to appear.

So, which season came first?

First, let’s remember that the whole Earth doesn’t undergo one season at a time. When it’s winter in England, it’s summer in Australia. And areas around the Equator only have two seasons, not four. This is due to the Earth’s 23.4° tilt.

Despite this constant tilt, in 4.6 billion years, the Earth’s seasons haven’t always been the same.

During the Cretaceous period, 66 million years ago – when dinosaurs reigned supreme – the average temperature was about 10°C higher than it is today. There wasn’t a huge difference between summer and winter and it would have been much wetter during all of the seasons. This climatic period lasted 79 million years!

Our most recent ice age (117,000 years ago) covered most of the Northern Hemisphere in giant sheets of ice, but it only lasted about 100,000 years. Even though the Earth was globally much colder, thanks to the its tilt, there were still distinct seasons.

So, which season came first? It’s hard to say… The origin and development of the seasons is too gradual and began too far in the past for us to know which one came first. It remains a mystery!

Thanks for your questions and stay curious!

This post was guest-written by Sarah de Launey, one of Life’s Exhibit Developers on the Projects Team.

Spring into the Easter Holidays with Life and enjoy our ever-popular chocolate workshops, hands-on crafts and a new Science Theatre show, as well as the last chance to catch our blockbuster exhibition Dino Jaws.

Dino Jaws at Life Science Centre

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