The Christian fish symbol is actually named ichthys or ichthus. It was used as a secret symbol of the Christian religion, although its origins are pagan.
Ichthys was the offspring of the ancient Sea goddess Atargatis, and the symbol was used to represent link to fertility, birth, and the natural force of women.
Fish are mentioned throughout the Gospels, with a few of the disciples being fishermen too. Today the “Jesus Fish” is frequently used as an icon of modern Christianity.