Why does ice float? When most substances get colder, they contract and become denser. Until it gets down to four degrees Celsius, water behaves like other substances and contracts, gets denser and sinks. At four degrees, water reaches its maximum density. At lower temperatures, water suddenly behaves very strangely and starts expanding. Equally, if you heat water from zero to four degrees, it contracts - the reverse of what happens to most other substances.
By the time water cools down to zero degrees, it is the top layer on the lake or pond. (Seawater freezes at a lower temperature because of the salts it contains.) When it turns to ice, water expands even more. Because ice is less dense than water, it floats on the surface of lakes and the sea.
This strange property of water means that the bottom of a lake or sea is usually free of ice, being four degrees or so, which is good news for fish. However, enormous floating chunks of ice are bad news for ships such as the Titanic.
Besides ordinary ice (ice I), eight other forms of ice (ice II, III, etc), have been discovered. These variants are formed under great pressure, such as inside a glacier, and are denser than ice I - so they might not float in ordinary circumstances.
Can flying fish really fly? Flying fish are often thought of as fish that can fly, but they actually glide rather than fly. They are long and slender with a large lower lobe on the tail fin. When escaping from predators, they propel themselves out of the water by rapidly moving their strong tails from side to side. Then they glide above the waves by beating their large pectoral fins, which act like wings to support them in flight. Flying fish glide as far as they can to avoid predators - sometimes more than 70 metres! They are one of the few vertebrates adapted for living at the surface of the ocean. Their bodies are usually metallic blue or green, blending in with the water perfectly.
Fishermen fish for flying fish at night when they come near offshore islands. Apart from being eaten as food, flying fish are used as bait for other fish such as marlin.
