matsya avatara
श्रुतिगणमपनीतं प्रत्युपादत्त हत्वा ।
दितिजमकथयद् यो ब्रह्म सत्यव्रतानां
तमहमखिलहेतुं जिह्ममीनं नतोऽस्मि ॥ ६१ ॥
śruti-gaṇam apanītam pratyupādatta hatvā
ditijam akathayad yo brahma satyavratānām
tam aham akhila-hetum jihma-mīnam nato ’smi
Salutations to the supreme god, who appeared as a gigantic fish, who restored the Vedas to Bhagawan Brahmā when Brahmā awakened from sleep, and who explained the essence of the Vedas to King Satyavrata and the great saintly persons.
A short story of the matsya avatara
When Vaivasvata Manu (son of Surya and the progenitor of humans) was giving tarpana in a river, a little fish entered his palm and sought refuge. Manu housed the fish in a small jar. As the fish grew, Manu kept transferring the fish in bigger vessels.
However, he ran out of resources when the fish kept on expanding; Manu realized the limits of his wealth and riches, thus breaking his pride. Manu then released the fish into the ocean, after realizing it was Vishnu himself.
Manu then learnt about the oncoming praLaya (destruction of the world). Vishnu asked Manu to gather all creatures of the world in a boat and be ready for the day of praLaya.
When praLaya in the form of a huge deluge arrived, Vishnu adopted the Matsya avatara (a huge fish with a horn). Manu then tied the boat to the fish’s horn, after which the Matsya led them to safety.