Biology Question #3988

Lisa Pearce, a 20 year old female from Gympie asks on November 7, 2007,

Whenever I drop a piece of cork, plastic or metal into a container of water, it always floats on top or sinks to the bottom. Some substances sink very slowly, but they always end up at the top or bottom. Fish quite happily ‘float’ at various levels. This is common in nature with different species being top, middle or bottom dwellers. How do fish manage this without having to use lots of energy swimming up or down all the time?

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The answer

Barry Shell answered on November 7, 2007

Fish are able to change their floatability, also known as buoyancy because they have an internal organ called a gas bladder. According to the Wikipedia page on fish gas bladders, fish can increase or decrease the amount of gas in these organs thereby changing the height at which they float in the water, without having to swim.

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