The adorable Swami of more fish is considered to be Lord Vishnu. Purushottam is a name of Lord Vishnu. Hence more fish is also called as Purushottam Mass. It is also called Mal Mass. There is a very interesting story related to this subject in Puranas. It is said that Indian scholars have determined a deity for each lunar month by their calculation method. Even though more months were to balance the Sun and Moon months, no deity was ready to be the lord of this extra month. Lord Vishnu accepted his request and thus it became Purushottam Mass just like Malmasa.