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Instant Smartarse #2: The One About the Sharks.

This is a bittersweet post to write. On our wedding day, back in January, a close friend of ours gave my new husband some advice: that we had both been running around at an exhausting pace and it was time to slow down. My husband and I are not exactly known for taking it easy, and had been running on pure adrenaline for about three months before the wedding, so this was excellent advice. We had been going so fast for so long that it had become normal, and we would often say 'just keep swimming', referring to our belief that sharks drown if they stop swimming, and sounding, we thought, like we knew some science.

Turns out we had a major misconception: sharks don't actually drown if they stop swimming. It is true that they mostly get their oxygen by swimming; the foward motion causes water to flow through their mouth and out over their gills, but they can make the water flow when they are not swimming by opening and closing their mouth and pushing the water over their gills that way instead. This is only half the smartarse story though - you could come unstuck when you share this little nugget with your non-smartarse friends if they ask any questions about how the gills work, so here's a little explanation to prevent any awkward moments:

The first awkward question could be 'what is a gill'?

Sticking with our shark, the gills are just behind those vertical slits at the back of the shark's head.

Under there it looks a bit like this:

There's lots of information in that diagram, but the gills are the little upturned V shaped structures at the bottom of the diagram.

The second awkward question could be 'how do gills work'?

The simple, smartarse answer is this:

The gill causes blood with very little oxygen to come close to water with a lot of oxygen in it, separated by just a few cells. The oxygen travels from the water to the blood by diffusion (passive movement from a high concentration to a low concentration), over the tiny distance between the arterioles and the water. This process is super-efficient as all those projections in each gill make the total surface area really huge, and the same is true for the surface area of all the tiny arterioles.

Image courtesy of

You can go super-smartarse and add that warm water kills fish. The warmer water is, the less oxygen it can carry. If it gets too warm there is not enough of a difference between the oxygen level in the water and the oxygen level in the fish's blood so oxygen movement slows down, the fish can't get enough oxygen so can't respire, and they die.

Watch out for future posts on diffusion and respiration as we've mentioned them here and any self-respecting Smartarse needs to be able to use these words fluently, but for now, you have enough info to be a fishy info fiend and I have to keep a promise to slow down, so the #instantsmartarse series is going to grow slowly.

Sadly, our friend who gave us the slowing down advice won't see that we took his wise words so seriously. Eddie passed away a couple of weeks ago, and it's his funeral today. He was such a lovely man and will be sorely missed. He leaves behind a beautiful family and lots of happy memories, and two Smartarses who have learned that we won't drown if we stop swimming.

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