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Ask Dr. Universe fish
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How do animals breathe underwater? – Kinsley, 9, North Carolina

Dear Kinsley,

Have you ever seen a diving beetle? They’re one of my favorite animals. They live underwater and breathe air from a bubble attached to their butts.

I talked about all the ways animals breathe underwater with my friend Wes Dowd. He’s a marine biologist and animal physiologist. He studies how living things interact with the world around them.

Animals need oxygen. For air-breathers like us, oxygen is mixed into the air. For water-breathers, oxygen is mixed into the water. To get oxygen into our bodies, we all need organs and tissues made of very thin material with lots of surface area. That means lots of places that touch the air or water where oxygen can pass through. Like inside lungs or gills. Or the skin of frogs, toads, newts and salamanders that can live on land or underwater.

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Are mermaids real? Is there a species that contains DNA that’s half human and half fish? – Maite, 12, Texas

Dear Maite,

People have thought about mermaids for a long time. Ancient people even drew humans with fish tails on cave walls. So, did they really see mermaids or were they drawing from imagination?

The marine experts from the National Oceanic and Atmospheric Administration (NOAA) say that no mermaids have ever been found in the ocean.

But we’ve fully mapped only about one-quarter of the ocean floor. There are probably between 700,000 and one million different kinds of plants and animals in the ocean. At least two-thirds of those are still unknown to us.

Does that mean mermaids could be swimming around in parts of the ocean we haven’t explored? Maybe. But our best guess is that people mistook other sea animals for mermaids—like manatees and their relatives.

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How do fish hear? — Lamarcus, 8, Ohio

Dear Lamarcus,

My goldfish roommate hates when people tap on his tank. The tapping sound he hears in the water is loud and scary.

I talked with my friend Rikeem Sholes about how fish hear. He’s a fish scientist. He studies salmon hearing at Washington State University.

He told me that a fish’s hearing system includes sensory cells in the inner ear and in a line along the outside of the fish’s body and head. Some fish also use their swim bladder to have super hearing.

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Do fish and sharks drink water? – Copper, 9, Florida

Dear Copper,

All living things need water. It’s how life works on Earth. But do animals that swim in water drink water?

I talked about that with my friend Nora Hickey. She’s a fish veterinarian at Washington State University.

She told me it depends on the kind of fish. Saltwater fish constantly drink water. Freshwater fish drink hardly any water.

It’s all about the salts inside their bodies. Those salts make their muscles and nervous systems work.

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How do you tell if your betta fish is happy or depressed? – Neely, 10, Oregon

Dear Neely,

As a science cat, I handle going to the veterinarian better than most. I see it as a meeting of scientific minds. But I had no idea some veterinarians specialize in fish.

I learned all about fish medicine from my friend Nora Hickey. She’s a fish veterinarian at Washington State University. She works in the Washington Animal Disease Diagnostic Laboratory. She helps fish at zoos and hatcheries stay healthy.

Hickey told me you can watch a betta's behavior to see if it's happy. Happy bettas swim around. They interact with things in their tanks and act interested when you come close.

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