Fish are, we are told, very light sleepers, and frequently
assume singular positions; but the most remarkable fact
concerning them is the change of color many of them undergo
while asleep.
Usually their spots and stripes become darker and more
distinct when they fall asleep. Occasionally the pattern of
their coloration is entirely changed. The ordinary porgy, for
instance, presents in the daytime beautiful iridescent hues
playing over its silvery sides, but at night, on falling asleep,
it takes on a dull bronze tint, and six conspicuous black bands
make their appearance on its sides. If it is suddenly awakened
by the turning up of lights in the aquarium it immediately
resumes the silvery color that it shows by daylight. These
changes have been ascribed to the principle of “protective
coloration,” and it has been pointed out that the appearance
of black bands and the deepening of the spots serve to conceal
the fish from their enemies when lying amid eel-grass and
seaweeds.--_Harper’s Weekly._
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