This avatar of Lord Vishnu was very interesting. It tells the story of the Satyavrata Manu, The Seventh Manu and the progenitor of the humanity or the ‘manavantara’. Satyavrata was the king of the Dravida Kingdom before the great flood.
One day Satyavrata was bathing in the Kritamala river. After bathing he started to pray to the Ravi or the Sun. During this ritual, one cups his hand, plunges it into the water and then let goes of it slowly while chanting a holy mantra. Suddenly while doing this, a small fish came into his hands. Seeing this he was about to throw the fish back into the sea, when something shocking happened. The little fish spoke and pleaded him to not throw it back to river. Satyavrata complied and kindly put the fish into a pot he was carrying.
After two days the fish grew in size and could not fit in the small pot so Satyavrata transferred it to a larger vessel. The same happened again. Like this it was transferred from the larger vessel to a well and then a pond. But when it could not fit into the pond, he carried it and threw it into the ocean. But as soon as, he did it the fish changed it shape and become humongous in size and transformed into a merman. It’s lower body was that of a fish and the upper torso resembled Vishnu. It had four arms and wore conical crown on the top of it’s head. It wore a shawl and a garland.
Satyavrata recognized it as Lord Vishnu and humbly bowed before it. Lord Vishnu stated that in exactly seven days, the earth will be totally flooded by water. He instructed Satyavrata to collect all the Saptarishi, and pairs of all birds and animals. He also instructed him to collect the seeds of all plants and there would be ship coming for them on the seventh day.
Meanwhile when this was happening, the demon Hayagriva(Horse-Face) had stolen the ancient texts from Lord Brahma when Brahma had yawned and accidentally had slipped the holy Veda’s from his mouth. Hayagriva had hidden himself in the ocean. The Matsya tracked him and had engaged Hayagriva in a fight. After a fight of two days Hayagriva finally lost and Vishnu took back the knowledge of Veda’s from the demon.
Seven days had passed. Satyavrata had collected all the beings that Matsya had stated him to. The whole world was in turmoil. Then suddenly a ship came into their view. It was being pushed by the Matsya who was in the form of a humongous fish with a one horn.
After they had all boarded the ship, Matsya requested that Vasuki, the king of cobra’s be the rope whose one end would be tied to Matsya’s horn and the other end to the ship. The Vishnu Guided the ship to the Himalayas and gave the knowledge of the Vedas, Puranas and Samhitas to Satyavrata. After the flood had receded, Satyavrata created humans and hence established humanity once again on the earth. After this, Matsya went back to Lord Brahma and the gave the Vedas back to him.