Srimad Bhagavatam Canto 08, Chapter 24, Text 29

SB 8.24.29

sarve lilavataras te
 bhutanam bhuti-hetavah
jñatum icchamy ado rupam
 yad-artham bhavata dhrtam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
All Your pastimes and incarnations certainly appear for the welfare of all living entities. Therefore, my Lord, I wish to know the purpose for which You have assumed this form of a fish.
Srimad Bhagavatam Canto 08, Chapter 24, Text 28
Srimad Bhagavatam Canto 08, Chapter 24, Text 30