Srimad Bhagavatam Canto 08, Chapter 24, Text 01

SB 8.24.1

sri-rajovaca
bhagavañ chrotum icchami
 harer adbhuta-karmanah
avatara-katham adyam
 maya-matsya-vidambanam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Maharaja Pariksit said: The Supreme Personality of Godhead, Hari, is eternally situated in His transcendental position, yet He descends to this material world and manifests Himself in various incarnations. His first incarnation was that of a great fish. O most powerful Sukadeva Gosvami, I wish to hear from you the pastimes of that fish incarnation.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The Supreme Personality of Godhead is all-powerful, yet He accepted the form of an uncommon fish. This is one of the ten original incarnations of the Lord.
Srimad Bhagavatam Canto 08, Chapter 24, Text 02-03