Most people only know about the fact the famous sage Vasishta, guru of Rama, was one of the mind-born sons of Brahma. But as I discuss in this question, Vasishta is no longer the son of Brahma. Currently Vasishta and his brother Agastya are the sons of Mitra god of friendship and Varuna the ocean god, produced by those gods out of attraction to the Apsara Urvashi. Here is how this chapter of the Srimad Bhagavatam describes it:
Agastya and Vasiṣṭha Ṛṣis were the common sons of Varuṇa and Mitra, the tenth son of Aditi. Upon seeing Urvaśī, the celestial society girl, both Mitra and Varuṇa discharged semen, which they preserved in an earthen pot. The two sons Agastya and Vasiṣṭha later appeared from that pot, and they are therefore the common sons of Mitra and Varuṇa.
But this excerpt from the Brihaddevata, an ancient work by the sage Shaunaka, provides an additional detail to the story:
Of these two Adityas [Mitra and Varuna], when they saw the nymph Urvashi at a sacrificial session, the semen was effused. It fell into a jar containing water that stood overnight. Now at the same moment two vigorous ascetics, the seers Agastya and Vasishta, there came into being. Now the semen having fallen in various ways - in a jar, in water, on the ground - the sage Vasishta, best of seers, was produced on the ground; while Agastya was produced in the jar, (and) Matsya, of great brilliance in the water.
My question is, what is the story of this figure Matsya who was born in the water? Did he also become a sage like his brothers Vasishta and Agastya? Is he mentioned in any other scriptures?
Now in my question here I discuss how in the Aranya Kanda of the Ramayana, Rama, before visiting the Ashram of Agastya, first visits the Ashram of "Agastya's brother." Could this brother be the same as Matsya?