SB 8.24.54

śrī-śuka uvāca
ity uktavantaṁ nṛpatiṁ
 bhagavān ādi-pūruṣaḥ
matsya-rūpī mahāmbhodhau
 viharaṁs tattvam abravīt
Synonyms: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; iti — thus; uktavantam — being addressed by Mahārāja Satyavrata; nṛpatim — unto the King; bhagavān — the Supreme Personality of Godhead; ādi-pūruṣaḥ — the original person; matsya-rūpī — who had assumed the form of a fish; mahā-ambhodhau — in that water of inundation; viharan — while moving; tattvam abravīt — explained the Absolute Truth.
Translation: 
Śukadeva Gosvāmī continued: When Satyavrata had thus prayed to the Supreme Personality of Godhead, who had assumed the form of a fish, the Lord, while moving in the water of inundation, explained to him the Absolute Truth.