1) Life is found at all depths of the ocean. As you will have seen if you played our underwater survival game, fish have recently been discovered as deep as 8,000 metres below the surface. We rarely see these fish as humans can't survive at such depths.

2) There are over 20,000 species of fish.

3) The largest fish in the world is the whale shark. A lot of people think that the blue whale is the biggest, but because whales have come to the surface of the sea to breathe, they are mammals, not fish. The whale shark gets it's name because it looks like a whale, but it can actually breathe underwater. It can grow up to 15 metres long and weigh several tons.

4) The smallest fish is the tiny goby which lives in lakes in the Philippines. It is usually about 1cm long.

5) The most common fish in the sea is a deepwater fish called a "bristle mouth." It exists in very large numbers at 500 metres or deeper all over the world.

6) Fish don't really sleep - they only rest. This is because most fish don't have eyelids and cannot close their eyes. Usually they just stop moving, either floating in one place or wedging themselves into a spot in the mud or coral. Some fish even build themselves a nest! Because they keep their eyes open, fish rest, but are also alert to danger.
Sharks are one of the few exceptions - they have eyelids and can close their eyes. However, even when their eyes are closed, they don't stop swimming.

7) Some small fish only live for a few weeks or months, while others like the sturgeon live for 50 years or more. All fish only live for as long as they can avoid predators and stay out of danger.

8) Nearly all species of fish lay eggs containing their young. However, some fish such as the sea perch and certain types of shark give birth to living young, just like humans.

9) All fish breathe oxygen, just like humans. For more information, visit the 'How fish breathe' section.

10) Fish swim by flexing muscles on either side of their body. They flex each side alternately, causing their tail to move quickly from side to side. This moves them forward through the water. Fins are used for balance, especially when fish are staying still.

11) The fastest fish in the world is the sailfish. It has been timed at 110km/h (68mph). Tuna and some types of shark are also very fast, reaching speeds of 80km/h (50mph).

12) Some fish - usually eels - can swim backwards. They don't often do it though, as they can't see where they are going.

13) We walk vertically, with our head positioned at the top of our body. Most fish swim horizontally, with their head positioned at the front of their body. The sea horse is one of the exceptions, and swims with its long, tube-like snout pointing directly upward.

14) Fish don't chew their food. Because fish have to take water in through their mouth to breathe, they don't chew their food like us, normally swallowing it whole or in large pieces. Sharks have sharp teeth, but they only use them to catch and hold their prey, or to tear it into pieces they can swallow. Some fish like rays have large flat teeth that they use to crush the shellfish they eat. Lobsters use teeth in their stomach, which is very near their mouth, to break down food.

15) Most fish are colour-blind, but can see shadings, reflected light, shape, and movement. This allows them to find their way around and catch prey in dark, murky waters.

16) Electric eels really do give off electricity, and can give other animals electric shocks of up to 650 volts. This is nearly three times as much electricity as comes out of a plug on the wall of your house, and could certainly hurt or even kill a human.

17) The slowest fish is the seahorse which travels at 0.01km/h.

18) An Octopus has three hearts.

19) Salmon can jump as high as six feet out of the water. Every year they swim up rivers to lakes and ponds to lay their eggs, and jumping out of the water helps them to swim against the strong current.

20) If a Lobster loses an eye it will grow another one.

21) Hermit crabs don't have their own shells. They find unused shells from other underwater creatures, and carry them around as their home.

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