Vishnu as Matsya, the fish incarnation fighting a demon. Gouache drawing.

Matsya, 'the fish' relates to an ancient legend of the fish and the deluge. The details of the avatars vary in different puranas, but the object remains the same. The incarnation was to save Vaivaswata, the seventh Manu and the ancester of the human race, from destruction by a deluge. In the Bhagavata purana there is a variation in which the demon Hayagriva carried off the Veda, while Brahma was reposing. To recover the Veda, Vishnu assumed the form of a fish and saved Manu as related above