Antarctic fish swim with ice in their flesh

The very protein that prevents Antarctica's fish from freezing solid also means they spend their lives carrying hundreds of ice crystals in their bodies, a New Zealand scientist has found.

University of Auckland biologist Dr Clive Evans has travelled to Antarctica for the past 20 years, with much of his research dedicated to fish and their uncanny ability to produce their own antifreeze.

In order to carry out their most recent research, Evans and a team of American researchers had to drill through 2m of sea ice at McMurdo Sound, drop a line and sinker and go fishing ... all in the name of science.

"You can easily catch 100 fish without any big effort," he told the Herald on Sunday, "but the water temperature is roughly -1.9°C and the air temperature is colder, depending on the time of year you're going down there. So one of the problems with fishing down in Antarctica is the fish freezes when you pull it up through the hole and into the air, so it's a bit of an unusual problem in that you have to keep the fish 'warm'. It's quite a tricky business."

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The ability of fish to produce their own antifreeze has been known for some years but the team aimed to discover the full implications of this.

They found it has required something of an evolutionary trade-off - the very stuff that prevents the fish from freezing solid also stops ice crystals from melting.

"Normally, water freezes and melts at the same temperature which, for fresh water, is 0°C. For salt water it's -1.9°C because of all the salt. If there's antifreeze present, it freezes at one temperature and melts at another."

Because the seas at McMurdo Sound never got warm enough to melt antifreeze-bound ice, the fish had to carry sharp crystals within their bodies.

This is the first time what is known as "superheated ice" has been observed in a living organism.

"Antifreeze stops an ice crystal from growing but, at the same time, it stops it from melting, so it's a double-edged sword.

"Then you begin to ask, how long can you keep ice inside you if it's circulating around your blood? It's kind of like a clot, an embolism in your blood, which could be lethal," Evans said.

The scientists believe fish store the ice in their spleens - the only known organisms to do so. It could have adverse physiological effects on the fish but none has yet been discovered.

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The implications of the research are complex.

The effect antifreeze has on ice crystals could translate into other areas such as drug research, where the structure of crystals could be vitally important.

The long-term temperature record of McMurdo Sound produced in the study is also the most comprehensive available and could prove of great importance to other polar research.

Evans' research, which is co-authored by Paul Cziko, Arthur DeVries and Christina Cheng, has been published in the Proceedings of the National Academy of Sciences.

Surviving the cold

Caption: Special 'antifreeze' proteins in the blood of several Antarctic fish species bind to ice crystals and prevent the creatures from freezing. A new study finds that the proteins also allow the internal ice crystals to persist at temperatures that normally would melt them. Credit: Paul Cziko Usage Restrictions: Photo may be used only to accompany stories about the research described in this release. Credit required: Paul Cziko.
Caption: Special 'antifreeze' proteins in the blood of several Antarctic fish species bind to ice crystals and prevent the creatures from freezing. A new study finds that the proteins also allow the internal ice crystals to persist at temperatures that normally would melt them. Credit: Paul Cziko Usage Restrictions: Photo may be used only to accompany stories about the research described in this release. Credit required: Paul Cziko.

• Antarctic fish ingest ice through eating and drinking.

• The ice is potentially lethal as it can accumulate and act similarly to blood clots.

• To combat this each fish produces anti-freeze proteins.

• These proteins bind to the ice crystals and inhibit their growth by preventing water molecules from adding to the ice.

• Marine scientists believe that macrophage cells consume the bound crystals, removing them to the spleen.

• But the proteins which prevent the growth of the crystals also prevent them from melting, and the cold sea environment never warms enough to melt the ice in their bodies.