Fish

In Celtic tradition spirits have been associated with springs and wells from the earliest times. In ancient Gaul the tutelary spirit was occasionally a god, such as Grannos or Borvo: more often the custodian of the healing spring was a fertility goddess, always beautiful, sometimes dangerous, and these female deities have metamorphosed over time into the faeries of popular tradition.

Sanctuaries were often erected at the holy site, as they were also in later, Christian centuries, and at them festivals were held. Because of their symbolic associations with fertility they played a part in the great religious feasts of the Celtic year, particularly Midsummer's Day, when the wells were visited and worshippers left votive offerings. This surely is the origin of the more recent, indeed, still current custom of dropping pins in the well or tying scraps of rag to a nearby bush. Water spirits in Gaul were known as 'Niskas' or 'Peisgi', possibly ancestors of Cornwall's degenerate modern 'piskie', though the word may derive from Old Celtic 'peiskos' or Latin 'piscos', both meaning fish.

Inspite of this possible fishy provenance Cornwall is, so far as I know, the only Celtic land in which the water spirit does not take animal form, though the 'merrymaids' of the Cornish coast are clearly diminished spiritual beings. Elsewhere:

"the spirit of the waters was often embodied in an animal, usually a fish. Even now in Brittany the fairy dweller in a spring has the form of an eel, while in the seventeenth century Highland wells contained fish so sacred that no-one dared to catch them. In Wales Saint Cybi's well contained a huge eel in whose virtues the villagers believed, and terror prevailed when any one dared to take it from the water. Two sacred fish still exist in a holy well at Nant Peris, and are replaced by others when they die, the dead fish being buried. This latter act, solemnly performed, is a true sign of the divine or sacred character of the animal. Many wells with sacred fish exist in Ireland, and the fish have usually some supernatural quality, they never alter in size, they become invisible, or they take the form of beautiful women." [MacCullach 1911]

The Manx Taroo Ushtey, or water bull, seems also to be a guardian spirit, though he has no particular association with wells. In Irish myth there are several wells containing 'salmon of knowledge', which acquire their mystic wisdom by eating the hazelnuts which drop into the water. In the ancient text 'Cormac's Vision' the hero sees a royal fortress with four houses in it, and a 'bright well' surrounded by ancient hazels. In the well were five  salmon, which ate the nuts as they dropped. In the palace Cormac meets Manannan the sea-god who reveals the Land of Promise to him and presents him with a magic cup and branch. Another hero/god, Diancecht, presided over a well whose waters healed the mortally wounded at the second battle of Moytura. In myth, as in much of the folklore material, wells and springs and the spirits which inhabit them are associated with healing, inspiration, and the ancient Druidic belief in metamorphosis, which perhaps was an expression of the transmigration of souls. Other water spirits, such as the each uisge, or water horse, the Manx Taroo Ushtey, the Cornish Merrymaids and the Goidelic Selkies are described as destructive, dangerous or ambivalent towards human beings.

The ambivalence of the fish symbol is of great antiquity and can be seen in many cultural contexts. Jewish tradition predicts a great battle between Leviathan and Behemoth, which will take place at the end of the world. As a result of this conflict the great fish Leviathan will be dismembered and served as food to the devout.

According to Jung, this dualistic split "corresponds to the doubling of the shadow (self) often met with in dreams, where the two halves appear as different or even as antagonistic figures. This happens when the conscious ego-personality does not contain all the contents and components that it could contain. Part of the personality then remains split off and mixes with the normally unconscious shadow, the two together forming a double and often antagonistic personality" [Jung 1959]

From this psychoanalytic standpoint the fish/monster represents the conflict between the light and dark aspects of the self. Christianity, interestingly, has emphasised the beneficent aspects of the fish symbol:
Christ made his disciples into 'fishers of men' and used fish to feed the five thousand. The fish was used by early Christians as a symbol of resurrection, and as such is still to be seen on rear windscreens. This
incorporation of pagan symbolism anticipates later cultural shifts in the Celtic countries. The pre-Christian holy wells were transplanted to a Christian context, a context which transformed rather than denied their spiritual force.

The association between the salmon and rebirth was present in the original myth. In an old Irish manuscript Tuan mac Carell describes the primeval invasions of Ireland, which he witnessed, to Saint Finnen. He also claims to have been incarnated successively as a stag, boar, eagle and salmon. In this last form he was caught and eaten by an Irish queen, who conceived him as a human child. Similarly the legendary Welsh poet Taliesin claims:

"I have been a blue salmon
I have been a dog
I have been a stag
I have been a roebuck on the mountain
I have been a grain discovered....
I rested nine nights
in her womb, a child
I have been dead, I have been alive.
I am Taliesin [Matthews 1991]

Fraser cites some interesting parallels from British Columbia where, among the Kwakiutl people, twins are believed to be transformed salmon, who are forbidden to go near water, for fear that they might revert to their original shape. Twins have the power to summon winds, make good or bad weather and heal the sick. Similar beliefs exist among the Nootka, who prohibit twins from catching, eating or even handling salmon. [Frazer 1922]

In conclusion, the sacred salmon represents the ancient sanctity of water, its power to destroy and create. At another level it may stand for the troubled human soul, in its perpetual struggle to reconcile itself to
itself.

Fish: Some cultures symbolized the Moon with a fish instead of a snake. Some Moon Goddesses were depicted with fish-tails, akin to mermaids.