When ice covers lakes, there is less oxygen to breathe, and most fish sink to the bottom. They remain very quiet but awake. Carp, however, flap their tails to cover themselves with mud and they go to sleep. When the lake ice melts and the oxygen levels rise they awaken.
Invisible enemies
Invisible enemies Researchers have found that animals can pass on
viruses through saliva or immune cells as well as through blood,
and don't necessarily show detectable levels of the virus in their
blood. This means that new strategies will need to be used to
control mosquito- borne illnesses such as malaria and yellow
fever. 29 JANUARY 2000, P. 10
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