The organ for breathing in fish is the:

**The reasoning** Fish live underwater and need to extract oxygen dissolved in water, not from air. Their specialized breathing organ is the **gills**. Here's how it works: water flows into the fish's mouth, passes over thin, blood-vessel-rich gill filaments, and oxygen diffuses from the water into the bloodstream while carbon dioxide moves out. This is called **gas exchange in an aquatic environment**. The gills are perfectly designed with a large surface area to maximize oxygen absorption from water. **Why the wrong options tempt you** - **Lungs (A)**: You might think "breathing = lungs" because that's what *we* use. But lungs extract oxygen from *air*, not water. Only a few special fish (like lungfish) have lungs. - **Skin (C)**: Some amphibians like frogs breathe partly through skin, so you might confuse them with fish. - **Nostrils (D)**: Fish have nostrils, but only for *smelling*, not breathing! **Quick takeaway** Fish breathe underwater using **gills** — think "gills for water, lungs for air" and you'll never mix them up again.