Antarctic Fish "Hibernate" in Winter

Helen Scales
for National Geographic News
March 6, 2008

Antarctic cod go "on ice" and take a nap during the long winter months, a new study shows.

The cod hunker down on the seafloor, reduce their feeding, and slow their heart rates—probably as a way to survive Antarctica's dark winters, when the fish might have a harder time spotting prey.

This is the first time fish have been seen actively becoming torpid—a state similar to hibernation in land animals—as part of an annual cycle.

"A lot of freshwater fish go [unexpectedly] dormant in winter because a drop in temperature lowers their metabolism," said study co-author Hamish Campbell, a zoologist at the University of Queensland, Australia.

"By contrast, these Antarctic fish actively reduce their 'cost of living,'" he said.

The findings appear this week in the journal PLoS One.

Dramatic Slowdown

Campbell and colleagues attached heart rate monitors to wild fish and tracked their movements for a year using acoustic tags.

"The fish became 20 times less active in winter compared to summer," said co-author Keiron Fraser, a marine biologist from the British Antarctic Survey.

"Antarctic cod are not the quickest swimmers, but in winter they become semi-comatose," Fraser said.

About every week or so the cod wake up and swim around for a few hours, the team observed.

"This is quite similar to 'denning' in bears, where the hibernation isn't so deep and the animals can be disturbed, then spend some time awake before going back to bed," Fraser said.

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