From the Antarctic: Taking heartbeat of a cold-fish survivor

By SIMON COLLINS at Scott Base

Zoologist Bill Davison has found himself the southernmost fishing spot on Earth - and the fishing's great.

For a month he has been fishing through a hole in sea ice 6km southwest of Scott Base, just 1km from the edge of the permanent ice shelf hundreds of metres thick.

Even the relatively thin sea ice - just 3.5m thick - underneath his fishing hut makes it hard to believe anything could live below it.

But when Dr Davison and two visitors sank their lines about 6m below the ice for two hours on Monday, they landed 20 fish averaging 15cm long. And that was a bad day.

"There must be just millions of them down here because we always catch them."

Dr Davison tipped the smaller ones back and took the rest to his Scott Base "laboratory" - a shipping container packed with tubs of various kinds of fish and a "fish treadmill" of flowing water designed to test a fish's heartbeat and fitness.

These fish are Pagothenia borchgrevinki, part of the unique Antarctic family of Notothenioids whose "antifreeze" saves them from freezing to death when they hit the ice.

The whole family are new on the block, Dr Davison says. They did not exist before the Drake Passage opened up between Antarctica and South America during the split-up of the ancient continent of Gondwanaland between 80 million and 170 million years ago.

Previously, the fish in Antarctica were much the same as in South America because it was one big continent.

When the passage opened, a belt of winds developed right around what is now a continuous stretch of Southern Ocean, isolating Antarctica from warm air and ocean currents from the north.

The continent, once perhaps as green in summer as northern Canada, froze over year-round and its existing fish died.

"Then we had a Notothenioid which could produce antifreeze, and it survived," Dr Davison says.

That first cold-adapted fish had the plankton and other marine organisms of a whole continent at its disposal, and quickly diversified into a range of species to feed on every available food source.

"They are all closely related. Some only diverged 5 million years ago. The chances are that the whole system is still speciating [splitting into new species]."

Dr Davison is studying a property of Antarctic fish not found even in their Arctic counterparts. Their hearts react to stress in the opposite way to other species.

From humans to trout, normal heartbeats are set low. When we strike stress, our bodies produce adrenalin to ramp up our heartbeats so that we can fight or run.

But the normal heartbeat of an Antarctic fish is high, and its body produces chemicals to slow it down so its scarce energy is not burned up too quickly in the harsh polar cold.

Dr Davison, a lecturer at Canterbury University, seems made for the job. Born in England, he taught veterinary anatomy in Kenya and became used to wide open spaces. He came to New Zealand in 1981 and has spent 18 summers in Antarctica.

But even here, human industry intrudes. Dr Davison worries about the impact of global warming on fish adapted to the cold. Borchgrevinki normally live at minus 1.9C, and can tolerate up to about 4C.

"At 6C they are dead," he says.

Already, studies on the other side of the Antarctic have found that higher temperatures have pushed the mackerel ice fish further south into waters still bearably cold. As each species pushes south, it may encroach on the territory of other fish.

The Pagothenia borchgrevinki, living the furthest south, will have nowhere else to go. It is at the end of the road.