Crabs, lobsters, crayfish,
shrimp, and some other crustaceans turn red/orange when cooked from
their typical blue-green to grayish color.
The exoskeletons of such creatures are made up of several pigments,
one of which is a carotenoid called astaxanthin, which provides it’s
reddish coloring (astaxanthin is the same carotene that gives salmon
its color). At normal temperatures and when alive the astaxanthin
pigments are hidden because they are covered with other protein
chains that give their shells the bluish-gray or brownish-green
color we see.
Exposure to heat destroys this protein coating, while the carotenoid
pigment, astaxanthin still remains stable. So when you cook a crab
or lobster or other crustaceans, the heat breaks down all the
pigments except for astaxanthin, causing the bright red color we see
in cooked lobsters, crabs, and crayfish or the reddish-orange color
of cooked shrimp.
Only the albino crab and lobster do not turn red when cooked because
they have no pigmentation, so they remain the same white color even
when cooked.
A one pound lobster is about seven to eight years old, and a eight
pounder may be 20 to 50 years old. Lobsters are capable of living
over 100 years.