Srimad Bhagavatam Canto 08, Chapter 24, Text 54

SB 8.24.54

sri-suka uvaca
ity uktavantam nrpatim
 bhagavan adi-purusah
matsya-rupi mahambhodhau
 viharams tattvam abravit
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Sukadeva Gosvami 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.
Srimad Bhagavatam Canto 08, Chapter 24, Text 53
Srimad Bhagavatam Canto 08, Chapter 24, Text 55