Matsay was the first incarnation of lord vishnu .
Matsay is the word in Sanskrit which means a Fish.Matsay avatar of vishnu has four hands holdin Chakra, Padma (flower), gadha and Shankha.
Vishnu is the protector and his ten Incarnations , were to protect the earth from Sins and Pralaya .
Story of Matsya Avatar:
long long ago before the earth met with its first Pralaya (destruction) , King Satyarata ( also called Manu) was washing his hands in a river just then a little golden fish swan into his hands, the fish pleaded Manu to take it with him. Manu had some pity on the innocent fish and kept it in a jar. The fish outgrew its size day by day , Manu transferred it to a pond and then into a river which meets the ocean. One day the fish revealed itself as Lord Vishnu to Manu, He warned him off the upcoming Pralaya, in which all three loks ( earth , skies and hell) will be destroyed by flood , in Seven days and advised him to collect all the Sapta Rishies (sages) , flora and fora,medical herbs, all type of seeds, good people of different spices, different Animals and Snake Vasuki. Lord Vishnu also told Manu that on the day of flood a huge, he will sent a huge boat for Manu and he along with all Collected valuable things and Sapt Rishies should board the Boat and when the boat will loose its balance due to strong winds then he himself in his Matsaya Avatar will come to rescue them and they shell tie the boat with Snake Vasuki to Matsay’s horn.
Seeking the advice of Loard Vishnu the King Satyavrat (Manu) collected the things and saptarishi and went on a mountain. At the seventh day the world broke into pralaya, as said before a boat reached Manu and they boarded it. They realized that they had every thing to revive life on earth but not the four Vedas . A deamon Damanaka ( also called Hayagriva), had stolen it and hide himself in a couch shell. Lord Vishnu fought with him and Rescue the Vedas.
Matsaya came to Manu and they tie their boat with Snake Vasuki to the horn of Matsay. Matsya pulled them to a safe island as soon as the pralaya stopped. Manu with Sapth Rishies started life on that island.