The ceasg is a

mermaid In folklore, a mermaid is an aquatic creature with the head and upper body of a female human and the tail of a fish. Mermaids appear in the folklore of many cultures worldwide, including Europe, Asia, and Africa. Mermaids are sometimes ass ...

Scottish folklore Scottish folklore (Scottish Gaelic: ''Beul-aithris na h-Alba'') encompasses the folklore of the Scottish people from their earliest records until today. Folklorists, both academic and amateur, have published a variety of works focused specifically ...

with the upper body of a beautiful woman merging with the tail of a

grilse Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus '' Salmo'') and North Pacific (genus ''Oncorhynchu ...

(a young salmon). She is also known in

Scottish Gaelic Scottish Gaelic ( gd, Gàidhlig ), also known as Scots Gaelic and Gaelic, is a Goidelic language (in the Celtic branch of the Indo-European language family) native to the Gaels of Scotland. As a Goidelic language, Scottish Gaelic, as well ...

as maighdean na tuinne ("maid of the wave") or maighdean mhara ("maid of the sea"). The ceasg lives not only in the sea but also in rivers and streams, and can be made to grant three wishes to anyone who captures her. Marriages sometimes occur between ceasg and humans, and famous maritime pilots are often reputed to be descended from such unions. Even when these marriages end and the ceasg returns to the sea, they will always take an interest in their human descendants, protecting them in storms or guiding them to the best fishing grounds. The ceasg is sometimes imagined as something more monstrous. In some tales she swallows the hero and he remains alive in her stomach. The hero's wife plays a harp until the mermaid is charmed and the hero escapes. When the wife stops playing the mermaid swallows her, and the hero must consult a wizard for help. He is told that he must obtain a special egg that contains the mermaid's life force. He obtains the egg, rescues his wife, and kills the mermaid by crushing the egg. In these stories the hero had been promised to the mermaid before his birth. His father had been childless and the mermaid promised him sons on condition that the firstborn would be given to her.Campbell, John Francis (auth.) and Henderson, George (trans.) (1911). ''The Celtic Dragon Myth''. Edinburgh: John Grant. pp. 33–40, 78–82. The Scottish folklorist Donald MacKenzie suggested that the ceasg may originally have been a

sea goddess A water deity is a deity in mythology associated with water or various bodies of water. Water deities are common in mythology and were usually more important among civilizations in which the sea or ocean, or a great river was more important. Ano ...

to whom human beings were sacrificed.

References

{{Scottish mythology Mermaids Scottish legendary creatures