The ichthys was a fish symbol formerly used quite widely as a
sacred symbol of the female vulva. The fish Goddess, Aphrodite
Salacia, was worshipped by her followers on her sacred day, Friday,
when they ate fish and engaging in orgies. Just as the early
Christians adopted pagan feast days in order to divert worship away
from pagan deities, so they adopted the fish symbol and ate fish on
Fridays, but of course did not engage in orgies. The original
symbolism has long been forgotten, and the symbol is now associated
by most Christians with the concept of 'fishers of men'.