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How do fish live?

Giant grouper swimming with other smaller fishFish live under water nearly all the time. They do not breathe air. Instead, they use their gills to take in oxygen from the water around them. Fish have fins and tails, and many are covered with scales. Most fish lay eggs, although some, including sharks, give birth to live young. Some kinds of fish live in fresh water (rivers and lakes) while others live in the saltwater of the oceans. There are two main groups of fishes: cartilaginous fish (sharks and rays) which have soft skeletons made of cartilage, and bony fish—all other fish—which have skeletons made of bone.



To breathe, fish open their mouths, and take in water that contains oxygen (1). When they pump it out through slits in the side...Read More >>To breathe, fish open their mouths, and take in water that contains oxygen (1). When they pump it out through slits in the side of their head, it passes over the gills and tiny blood vessels take in the oxygen (2).

Living underwater

Many fish have streamlined bodies with fins, a tail and a coat of overlapping scales. They breathe using gills. They draw water, which contains oxygen, into their mouths. When they pump it out through slits in the sides of their head, their gills take in the oxygen. Most fish lay thousands of eggs in the water, although many of these eggs are eaten by predators before they hatch.
 

Defence

At top speed, a bluefin tuna could swim faster than a greyhound, zebra or hyena could run.

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