DO FISH SLEEP?

Dag Stenberg stenberg at cc.Helsinki.FI
Sat Jan 21 08:13:41 EST 1995


ZAMPINO (zampino at aol.com) wrote:
} If so how? 

Yes, they are considered to do so. A great number of fish species have
been studied in this respect. At times, they stay still in a
typical posture, and may search for a specific place in which to rest
like this, as do other animals. Some burrow into the sand bottom, other
hide between stones. While "sleeping" the fish are less reactive than
otherwise, just like other animals. While they cannot close their
eye-lids, some can rotate the eyes inward. Some sharks do have eyelids, 
and close these. The gills are reported to move more slowly, so the
"breathing" is reduced. 
  The sleep of fish, though, differs in many respects from that of birds
and mammals, as there are considerable differences in brain structure
and function. It has been very difficult to record the
electroencephalogram, but some differences between acitve and rest
("sleep") states have been found. 
  It is also considered that fish do not have REM sleep at all.
  Some fish are always moving about. Apparently they can maintain
posture by small fin movements while sleeping.

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