Matsyavatara

Matsya Purana and Bhagavata Purana elaborate on the narrative of this avatara, its significance and purpose.

King Manu had renounced the world and did a lot of austerities. Brahma the creator pleased with his austerities granted him the wish to rescue the world at the time of the Pralaya [the great Deluge].

One day Manu was about to offer water as part of his austerities he found a tiny fish in his palm. He was about to throw it away, when the tiny fish pleaded him to protect him from bigger fish. So Manu let it into his kamandala but soon it outgrew his kamandala and had to be transferred to a pot, then to a bigger vessel, then to a pond, then to bigger water resources.

Manu realized that it was not an ordinary fish but Lord Vishnu himself and prayed to the Lord.

Lord Vishnu informed him that the time of pralaya was approaching and ordered him to collect samples of all grains, plants, and animals and wait for a big ship to arrive. As soon as the ship arrived he had to tie it to the horn of the mammoth fish.

When the pralaya started, Manu did as he was told. He tied the ship to the Great Fish with the help of Vasuki [the serpent] and helped everyone to safety till the deluge was complete.

Meanwhile, Brahma (whose day is equal to one kalpa at the end of which the pralaya takes place) was feeling sleepy and involuntarily took a yawn. Somakasura (also known sometimes as Hayagriva) slipped in and stole the Vedas from the yawning mouth of Brahma and ran away to hide in the deep waters of the ocean.

The Vedas being necessary for the creation at the beginning of the new Kalpa (World or Generation), the Devatas went to Lord Vishnu pleading with him to rescue creation by retrieving the Vedas.

Lord Vishnu who had already taken the incarnation of Matsya went to the deep of the ocean killed the demon Somakasura and got back the Vedas just in time for the renewal of creation in the new Kalpa.