How do fish survive in sub zero temperatures

A.� They use two mechanisms: notothenioid, to give them their official name, fish can tolerate the presence of ice crystals within their bodies and they have anti freeze in their blood.

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Q.� How do the ice crystals get into their bodies

A.� The ice crystals are always present in the water around them and are eaten and breathed by the fish, making their way to the skin, stomach, gut and kidneys.

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Q.� But not the blood

A.� No, the ice crystals are absent from the muscles, blood and the remaining internal organs.

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Q.� So what protects these organs

A.� The second mechanism: antifreeze. Special proteins, known as anti-freeze glyco proteins, are secreted to prevent ice crystals from forming and growing where they are not wanted within the fish's blood and tissues.

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Q.� How does the anti freeze work

A.� The anti-freeze proteins are just the right shape to smother the ice crystals, blocking the build of water molecules and preventing the crystals from growing.

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Q.� How low can they go

A.� In experiments notothenioid fish's natural anti-freeze is so effective that they can survive in water as cold as minus 8 Celsius with no apparent ill effects.

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Q.� What does freezing normally do to the blood

A.� For non-arctic animals it's fatal. Ice crystals are lese dense, and therefore much bigger than the water from which they form. As the ice crystals grow they tear the delicate walls of the cells, once the ice melts this damage cannot be repaired and the cell dies. Eventually, if this is widespread throughout the body, the organism itself will die

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Want to know how an animal survives in its apparently hostile environment Click here to ask.

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by Lisa Cardy