Paul Klee: The Golden Fish
G.G. Jung on Fish Symbolism
The serpent is an equivalent of the fish. The consensus of opinion interpreted the Redeemer equally as a fish and a serpent; he is a fish because he rose from the unknown depths, and a serpent because he came mysteriously out of the darkness.
Fishes and snakes are favourite symbols for describing psychic happenings or experiences that suddenly dart out of the unconscious and have a frightening or redeeming effect. That is why they are so often expressed by the motif of helpful animals. The comparison of Christ with the serpent is more authentic than that with the fish, but, for all that, it was not so popular in primitive Christianity.
The Gnostics favoured it because it was an old-established symbol for the “good” genius loci, the Agathodaimon, and also for their beloved Nous. Both symbols are of inestimable value when it comes to the natural, instinctive interpretation of the Christ-figure. Theriomorphic symbols are very common in dreams and other manifestations of the unconscious.
They express the psychic level of the content in question; that is to say, such contents are at a stage of unconsciousness that is far from human consciousness as the psyche of an animal… The snake does in fact symbolize “cold-blooded,” inhuman contents and tendencies of an abstractly intellectual as well as a concretely animal nature: in a word, the extra-human quality in man.Collected Works of C.G. Jung Volume 9 (Part 2): Aion Page 186