The Matsya avatar was the first incarnation of Lord Vishnu to restore dharma on earth. In Satya Yuga, Lord Vishnu becomes apparent as the savior when adharm surfaces. Matsya avatar is the very first among the remaining ten different incarnations of Lord Vishnu.
The story behind the Matsya avatar is a tale described in the Vedas. Usually, when a Kalpa was about to end, Lord Brahma goes to sleep, uttering the Vedas half-consciously. At that time, a deluge was about to happen to mark the end of the Kalpa. Lord Maha Vishnu is the Matsya to assure the continuance and growth of life on the planet.
Lord Vishnu wanted to save the sage, Satyavrata and other pure beings on earth. He took the form of a small fish. The small fish glided into the hands of the sage who was offering his daily prayers. He was about to put the small fish into the water but the fish pleaded the sage to save it from other big creatures that could kill it.
Satyavrata was moved and put the fish in a jar and kept it in his house. The fish grew in no time. Satyavrata shifted the fish to a pond and it outgrew the size of a pond. He shifted the fish to the ocean and it again outgrew the size of an ocean. Satyavrata recognized that it was not a normal fish but a divine one. He bowed down and worshiped the huge fish. Lord Vishnu seeing his devotion revealed Himself and was told that He was there to save Satyavrata.
The fish then warned him of the approaching cataclysmic floods. The Great Flood would occur in a week that would destroy all life. “Just a week from now, the ocean will rise and inundate the entire Universe. At that time you will see a spacious boat approaching you. Do collect all the seeds, plants and animals required for the next spell of creation and get into the boat and wait for me. Take Vasuki, the kind of Serpents, with you. The seven Sages will also be with you” it said. Satyavrata immediately prostrated before the Fish.
Sage Satyavrata then got on a boat along with the seven rishis and seeds of all created things and was led by the giant fish. The fish had a horn and had turned golden in color. The boat was tied to the horn of the fish with a serpent. It is said that the deluge destroyed the entire universe. The boat settled safely on the Himalaya mountain saving Satyavrata and the other creatures as the next Yuga began. All the seeds that were brought were gathered and planted on the earth for new cultivation and vegetation. Thus the rishis survived along with some “seeds of life” to re-establish life on earth.
Fulfilling the responsibility of being a protector, Matsya avatar of Lord Vishnu. Matsya gave a new life and civilization again dawned upon Manu and his people. The basic core of avatar is there is no beginning or end its just the transformation. When adharma will be on rising nature starts its destructive transformation, then to restore Dharma and save people from the evil, the Lord incarnates to maintain the cycle as it was before the destruction.