Raja Parikshit inquired from Shukadeva why the Lord had taken the form of a fish, which seemed to be a lowly form subject to karma. Shukadeva replied that the Lord takes on various incarnations as needed, and although he pervades all beings, he is not affected by the qualities of the bodies he occupies. Shukadeva went on to explain that at the end of a kalpa, Brahma retires and a periodic deluge takes place. During the last kalpa, the Vedas were stolen by an asura named Hayagriva just as Brahma was about to sleep. The Lord then appeared in the form of a fish to retrieve them.
At that time, there was a king named Satyavrata, who was devoted to the Lord and was performing austerities by the Kritamala River. One day, he noticed a tiny fish in his hand as he was about to offer water. The fish pleaded with the king not to return it to the water where it would be preyed upon and asked for protection. The king took pity and kept the fish in a jar, which it quickly outgrew. The fish continued to grow, and the king moved it to larger and larger bodies of water. Eventually, the fish revealed itself to be Lord Hari in disguise and told Satyavrata about the impending deluge and how he should prepare for it.
After seven days, the Lord appeared in his incarnation as a huge gold-colored fish and sent a ship to Satyavrata. The king and the Saptarishis, along with representatives of all plant and animal life, boarded the ship, which was tied to the fish with Vasuki as the rope. The Lord then gave spiritual instructions to Satyavrata and the sages during the deluge. When it was over, Satyavrata became Vaivaswata Manu of the new cycle of creation, and the Lord returned the Vedas to Brahma.